[RavenTai]

Originally Posted by Rookie2

Sorry RT, can't help much with the heavy circuitry. I did try to email tech support for Yazaki Meter last week, to ask what was done to the circuitry to create the flat spot in the gauge. No response yet.


Rookie2

Good deal, I am pretty sure the flat spot caused by the zener diode but it would be great to get confirmation, also if they respond it will surely give some other useful info.

Thank You,

Originally Posted by Gauge

RavenTai,

You are an amazing dude!

Keep plugging away. I have absolute faith in you.

BTW - what do you do for a living - Rocket Scientist?

Thanks you, but electronics on this scale is not beyond any one here, a couple hours of basic electricity would get you there. I am an aircraft mechanic (A&P/AMT) at a major airline (dying). I had some basic electricity and avionics classes in school and have dabbled with computers and automotive electricity since then.


I’ll keep playing with it but to come up with a mod I am going to need a gauge to test it on, if you see a gauge or cluster for sale at a reasonable price let me know.

[Gauge]

Aircraft Mechanic - Rocket Scientist - Close enough You are still way out of my league. For all I know a Zener Diode could be another name for "Muffler Bearings".

Like I said, I have faith in you man!

BTW - I don't think a couple of hours of "basic electricity" will get me to your level of understanding, but if you believe in me, I guess I should take that as a compliment.

Thanks for using your knowledge to help solve this.

[Heffenoche]

This may be a little too basic for this thread but once one installs a temp gauge, what is normal operating temperature? Than at what temp would one become a little concerned and at what temp would one pull over and shut it down and at what temp am would one be fairly certain they have done severe damage?

My guesses, to see how wrong I might be:

Normal operating temp 175-190
A little concerned 191-220
Pull over & shut down >221 (226 ac cuts off)
Eminent damage >240

[Photoman]

I was curious about the chart data I had posted so I set the temp sensor up again and ran the numbers. The equipment I used both times was a Raytek ST80 Pro with the remote temperature probe, and a R Shack Micronta multimeter. I put 15w-40 motor oil in a cup that I used as the medium to heat up with a Coleman stove. I took a pic of the test setup but it turned out pretty messy. If anyone wants it posted let me know. The meter was set on the 200 Ohm scale. I’ve been messing with this all day and keep getting different numbers. If I test with the oil heating up it’s one set of numbers, and cooling down a different set so I think I needed a larger oil volume. Here is a pic of the best numbers I could come up with. If anyone wants an Excel chart/file, PM me with your email address. I would just use the chart for reference. Basically, from 175-200 F the temp changes 2 degrees per ohm. 200-210 3 degrees per ohm. 210-220 4 degrees per ohm. 220-230 5 degrees per ohm. 230-245 6. 245-260 7. From 28 ohms at 175F to 5 ohms at 260F. Good luck.

Bill

[Rookie2]

Originally Posted by RavenTai

Thanks you, but electronics on this scale is not beyond any one here, a couple hours of basic electricity would get you there.

If you aware of a good beginers manual for learning basic circuitry and testing, I'd love to read up and learn more. I had a 100 level EE circuits class about 15 years ago, but most all that has left me. I know about how to turn my voltage meter on, but I still find myself finding out that something is hot... the hard way .


Rookie2

[RavenTai]

Originally Posted by Gauge

For all I know a Zener Diode could be another name for "Muffler Bearings".

Like I said, I have faith in you man!

Thanks for using your knowledge to help solve this.

no problem, I want a accurate cluster gauge also, when I figure out how to do so I will be glad to share the info back to a community that I have learned a lot from.

Just so you know, a diode is an electrical check valve. It allows current to flow one way but snaps shut preventing current in the opposite direction.

A zener diode is a special kind of diode, like a diode it allows foreword current and stops reverse current but if the voltage of the reverse current gets to a certain pre set level it will allow this reverse current to flow.

This range between where the current just starts to reverse and when the zener diode finally lest some of the current pass is where the flat spot in the gauge comes from, during the flat spot the circuit is artificially balanced and the needle does not move

BTW - I don't think a couple of hours of "basic electricity" will get me to your level of understanding, but if you believe in me, I guess I should take that as a compliment.

It is intended as a compliment, all the members here seam to be pretty smart. This circuit is not too bad, with the proper tools you could figure this one out.

Originally Posted by Heffenoche

This may be a little too basic for this thread but once one installs a temp gauge, what is normal operating temperature?

That is actually quite important,

1. I would also like to know what those with real gauges are seeing for typical temps. CDan has posted his recent experience above but his 80 is not at all typical in relation to temperatures. this info will be needed to calibrate a linearized gauge. I would still like my fixed gauge to point to the middle when it is at its average temperature. This typical temperature may be different with different weather but would like to get it close. Adjusting the value of the resistor R1 should adjust what temperature the gauge centers at. Assuming the two inductors (L2 and L3) have the same resistance then when the resistor R2 (thermistor) and R1 (set resistor) have the same value the bridge will be balanced and the needle will be in the center

2. I would also like to know what people think would be a good range for this gauge. How high and low do you want to see? A tight range will show the slightest changes in temperature. But miss the extreme highs and lows. A wide range will allow you to watch it warm up on the cold side and also watch your motor melt on the high side.

At first though I am thinking I want a tight range, don’t care to read much below a certain temperature. Pegged “cold” will be good enough for me. At the other end I don’t care to read extremely high temperatures. A pegged gauge at “holly s*!t that’s hot you should have shut down long ago idiot” is good enough. But maybe there are some reasons to see wider ranges?

I am a little less certain how this can be adjusted but I think a resistor in place of the zener diode will give a wider range, the higher the resistance of this new resistor the less sensitive the gauge and the wider the range. For a tighter range we will not be able to go below no resistance, or basically a wire in place of the diode whatever range of temperatures that gives. A no resistor gauge should show slightly narrower than it shows stock.

Resistors could also be added in series to the L2 and L3 inductors to do other things but those would be more difficult to add.

Originally Posted by Photoman

I was curious about the chart data I had posted so I set the temp sensor up again and ran the numbers. The equipment I used both times was a Raytek ST80 Pro with the remote temperature probe, and a R Shack Micronta multimeter. I put 15w-40 motor oil in a cup that I used as the medium to heat up with a Coleman stove. I took a pic of the test setup but it turned out pretty messy. If anyone wants it posted let me know. The meter was set on the 200 Ohm scale. I’ve been messing with this all day and keep getting different numbers. If I test with the oil heating up it’s one set of numbers, and cooling down a different set so I think I needed a larger oil volume. Here is a pic of the best numbers I could come up with. If anyone wants an Excel chart/file, PM me with your email address. I would just use the chart for reference. Basically, from 175-200 F the temp changes 2 degrees per ohm. 200-210 3 degrees per ohm. 210-220 4 degrees per ohm. 220-230 5 degrees per ohm. 230-245 6. 245-260 7. From 28 ohms at 175F to 5 ohms at 260F. Good luck.

Bill

Bill thank you for the updated chart and info, do you think the internal temperature of the thermistor lagged behind the temperature of the oil?

If you don’t mind I would like the see the test setup and any advise on other ways it can be done. I will be doing something similar to test the entire gauge circuit.

PM coming your way.

Originally Posted by Rookie2

If you aware of a good beginers manual for learning basic circuitry and testing, I'd love to read up and learn more. I had a 100 level EE circuits class about 15 years ago, but most all that has left me. I know about how to turn my voltage meter on, but I still find myself finding out that something is hot... the hard way .


Rookie2

I had a Glencoe text book,
Aircraft Electricity and Electronics in school, it does a good job of explaining basic theory both AC & DC that would apply to all electronic devices and then goes on to explain aircraft systems both general aviation, witch is very much like 1950’s automotive, alternators, magneto’s, batteries etc and also commercial with is more complex and specialized with communication, radar, navigation, specialized systems, etc. The later parts of the book may not be that useful to you beyond just information but at the used price (4$-20$) it is worth having IMO. I don’t think it would pay for you to buy a new one at $60.

I am sure there are some books more specific to what you are looking for, but I have not read any beyond the above to be able to give any advice on them. Maybe a trip to the library?

There is also a lot on the web, I use Google searches to get refreshers on formulas and components.

Here are some on-line primers. Learn Ohm’s law first. Learn it until you are tired of it. It is the core of electronics. Ohms law is simple to use (multiply and divide) but powerful to apply, using some known values it can solve for unknown values with certainty.

Learn about resistors in parallel and series then you can move on up. Go ahead and work the math examples just reading will not get you a working understanding.

http://www.autoshop101.com/autoshop16.html

http://www.allaboutcircuits.com/

http://www.electronics-tutorials.com...arting-out.htm

http://hyperphysics.phy-astr.gsu.edu...ic/ohmlaw.html

[Photoman]

Bill thank you for the updated chart and info, do you think the internal temperature of the thermistor lagged behind the temperature of the oil?

If you don’t mind I would like the see the test setup and any advise on other ways it can be done. I will be doing something similar to test the entire gauge circuit.

RavenTai,

I think the speed at which the small amount of oil heated up affected the results by creating temperature layers. Along with that, the probe depth with this amount of oil appears critical. The sensor has to be near the top of the oil in order to keep the ground preserved (not shorted in the oil). I tried to match this depth with the probe tip to keep the temp readings as accurate as possible. To do this test correctly in my opinion, a larger amount of oil should be heated more slowly. Possibly doing the test backwards by heating the oil, then taking the readings as it cools, with some agitation, may work better (but much slower). The first time I did the test I used a small propane torch and played the flame on the cup, heating the oil more slowly. This time, even on it’s lowest setting, the propane heater caused the temps to rise rapidly. It would have been better with two people, one to call off the readings and the other to record them. As it was I just held the trigger down on the IR gun, and took the probe readings every 1 ohm change.
The setup in the pic has a blue cup with the oil in it. On top of that I just used a small piece of thin plywood drilled to fit the sensor and beside that, drilled for the probe. I made sure the oil level was up on the sensor and the probe was at that same height. I did have to put a large washer under the cup to get it to fit the Coleman; but I don’t think that would affect anything. A little macro tripod to hold the wires away and that was it. Pretty booty fab.
The first pic shows the whole setup. The second closer pic shows a meter reading of 172.6 which was at oil and ambient 73 F. Let me know if you need anything else.

Bill

[cary]

Important question, what kind of oil did you use for the test?

Seriously, I am so glad that someone is finally working out a fix. My electrical skills are limited to crossover design, and I haven't done that in years.

Concerning the range of the guage, I would say a wide range. This would keep the guage from bouncing like a pogo stick every time you speed up or slow down, but would show when the motor starts to heat up.

[Rookie2]

Originally Posted by RavenTai

I had a Glencoe text book,
Aircraft Electricity and Electronics in school, it does a good job of explaining basic theory both AC & DC that would apply to all electronic devices and then goes on to explain aircraft systems both general aviation, witch is very much like 1950’s automotive, alternators, magneto’s, batteries etc and also commercial with is more complex and specialized with communication, radar, navigation, specialized systems, etc.

Awesome. Got one on the way. This is perfect, learn a little about electronics, and have another resource for enhancing the GA knowledge.


Rookie2

[semlin]

great work guys, this is fun to read...

concerning the average temp, I suspect that will fluctuate somewhat between trucks. So many possible variables in the vehicle to affect temp and so many miles on them. I would suggest instead targeting the standard thermostat opening temp at say 1/3 or 1/4 of the dial.

I vote for a wide range that would include all possible operating temps. I think that once we have the flat spot eliminated, a wide range will have enough sensitivity for what we need. A significant gauge bounce every time you went up a hill or stopped at a traffic light would be distracting.

Once we have a working gauge, It would also be great to have an overlay sticker to apply directly to the gauge face (not the bezel) with a few data points. That seems like a job for a graphic design person to come up with something that looked reasonably oem.

Another thought I have had on the LED alarm issue is that the turbo diesel 80's have an LED light in the tachometer instrument face to indicate when the turbo is on. The tach is otherwise identical so I wonder if the 80 gas series tachs might already have a ready made mounting point and punchout hole for an LED that could be drilled to allow for this as a temp alarm.

[Gauge]

Originally Posted by semlin

I vote for a wide range that would include all possible operating temps. I think that once we have the flat spot eliminated, a wide range will have enough sensitivity for what we need. A significant gauge bounce every time you went up a hill or stopped at a traffic light would be distracting.

Actually I don't mind watching the gauge rise when I am climbing a hill and go down when I am descending - at least I know that my gauge is working. And if my engine gets hot, even if it is for a short time, I don't mind knowing that.

Originally Posted by semlin

Once we have a working gauge, It would also be great to have an overlay sticker to apply directly to the gauge face (not the bezel) with a few data points. That seems like a job for a graphic design person to come up with something that looked reasonably oem.

We should consider doing this for the Oil Pressure gauge as well - maybe throw some PSI amounts next to those tick marks.

Just my $0.02

[turbocruiser]

Wow, great reading, great posts, great thread, however, and i super sincerely hope not to offend any at all, there are way way way too many great guys with great minds here spending way way way too much time on this problem. I say this for several specific reasons:

1. No matter how you electrically engineer the stock gauge to get more accuracy you are still working with something that is not marked and not metered and something that will travel only 1.5 inches or so from completely cold to dangerously hot. When you consider the travel to the top of the gauge from the middle of the gauge where normal operating temperature is you have something that will travel only .75 inches or so. Suppose the stock needle on the stock gauge moves some 1/8th of an inch up from usual operating postion??? Well, so what? What would that temp be? What would the temp be at another 1/8th of an inch. Basically by doing this you are reverse engineering the "fix" that toyota made to prevent people panicing and pulling into the dealer to declare an overheat. YOU DONT WANT TO DO THIS!

2. No matter how you plug and play an OBD setup to show the true temps, you have some huge (laptop) or small (pda) display full of all sorts of settings that you have to refer to to tell true temps. YOU DONT WANT TO DO THIS WHILE DRIVING! Sure, an OBD setup would be sweet, and I still hope to have one, BUT, short of recording an entire driving event and reviewing it later, you cannot safely repeatedly refer to some such display while driving. The OBD option would be wonderful with willing copilots to tell the temps, and, it would be wonderful to review an entire driving event at a later time, and, it would be wonderful to determine the capability of cooling systems in general in garage while parked, but again, not while driving.

3. Any attempt at fixing some sensor to the block or the head or the rad is going to give false data; unless the sensor is in the coolant, you do not know the temp of the coolant, period.

With these things in mind, my own opinion is that the only option for telling the true temps is with wide range accurate aftermarket meters such as the Greddy Gauge I use, the ISSPRO Dan and others use, the Blitz that Reffug uses, or with the HKS plug and play temp thing I have posted here before. You really need something simple, and something setup right in regular view. If you have to pull the eyes from the road you recklessly risk real problems.

Again, I hope not to offend any at all, its just one of those things where the incredible collective intelligence here is solving a problem (shitty stock gauge) that should NOT be solved. Get a good aftermarket gauge, install it in an easily seen spot, and call it good. Trust me, this modification done this way will easily end up as the absolute most "peace of mind" modification you make. HTH

[turbocruiser]

A pic of sensor ...

[turbocruiser]

A pic of gauge ...

[clownmidget]

that's hard to miss and nicely covers that annoying burned out "D" at the same time An unbeatabel mod!

I'm curious why you didn't just "T" into the coolant line you already have going over to the turbo? It still looks slick and perfectly fine where it is.

[cruiserdan]

Did you see how much gas he has left? That's gotta be at least 50 bucks worth..

[turbocruiser]

Originally Posted by clownmidget

that's hard to miss and nicely covers that annoying burned out "D" at the same time An unbeatabel mod!

I'm curious why you didn't just "T" into the coolant line you already have going over to the turbo? It still looks slick and perfectly fine where it is.

Thanks, yes it is indeed hard to miss and only covers over the "D" and part of the "CRUISE" light when cruise control is on. It completely avoids covering any other idiot light which is wonderful cause I need all of em!!! The picture perspective is weird though; since I had to shoot the camera through the top of the open steering wheel section, it makes the gauge look a lot bigger than it is, but we basically get the idea.

As far as "T" ing into the coolant line to the turbo, to be truthful, I just did not think of it, but since you did, and now since I am, the probe tip is pretty long and I am thinking that the thing should sit immersed in as much coolant as possible - finding an adaptor to do that might be more difficult and because the basic Greddy adaptor was so simple, I just went with that. Also, I really wanted to know the temp that the coolant was JUST before returning to the rad so that spot made the most sense to me.

Anyways, thanks again.

[turbocruiser]

Originally Posted by cruiserdan

Did you see how much gas he has left? That's gotta be at least 50 bucks worth..

Yea, I always run with alota gas!

[Rich]

I don't think extreme precision is required from the coolant temp gauge. Here is all I really need to know 1) is the engine warmed up and running at normal operating temp, 2) is it running hotter than normal, but at a fixed temp and not increasing, 3) is it running hotter than normal and continuing to increase, approaching too hot, and 4) is it running too hot.

The factory gauge omits displaying category 2 and 3 info listed above. If the display were more linear, even without degree markings, I would have all the info I need. I would do a one time calibration to determine where "too hot" begins on the gauge.

[Rich]

Regarding the temp chart I posted a long time ago, which I believe Raven refers to: I did the test in a water bath, which is why the cutoff temp is below 212. I used an uncalibrated lab thermometer mark in single degrees C, and good quality Fluke multimeter last calibrated in the previous century. I recorded and plotted the change in resistence for each degree centigrade change in bath temperature, stirring the water bath constantly with the thermometer.

It is possible that the water vapor on the sensor skewed the resistence measurements.

[turbocruiser]

Originally Posted by Rich

I don't think extreme precision is required from the coolant temp gauge. Here is all I really need to know 1) is the engine warmed up and running at normal operating temp, 2) is it running hotter than normal, but at a fixed temp and not increasing, 3) is it running hotter than normal and continuing to increase, approaching too hot, and 4) is it running too hot.

The factory gauge omits displaying category 2 and 3 info listed above. If the display were more linear, even without degree markings, I would have all the info I need. I would do a one time calibration to determine where "too hot" begins on the gauge.

Get an accurate aftermarket gauge where you really can read the very wide range of temperatures and the very wide range of situations that cause those temperatures and you will completely change your mind on that thought. Until then you are just guessing, and guess what, you are guessing wrong! Besides, your gauge IS NOT linear now so you only have condition 1 above; by the time you get to condition 4 on your gauge it is likely too late.

[turbocruiser]

Originally Posted by Rich

Regarding the temp chart I posted a long time ago, which I believe Raven refers to: I did the test in a water bath, which is why the cutoff temp is below 212. I used an uncalibrated lab thermometer mark in single degrees C, and good quality Fluke multimeter last calibrated in the previous century. I recorded and plotted the change in resistence for each degree centigrade change in bath temperature, stirring the water bath constantly with the thermometer.

It is possible that the water vapor on the sensor skewed the resistence measurements.

Just like the stock gauge, a temp chart that stops at 212 is only showing part of the picture. You should have at minimum used a water/coolant mixture so you could raise the boiling point of using only water especially since there was no pressure induced through the test to raise the boiling point. Ideally you should have used oil so that you could go to 250 or so. Not a criticism, just an observation.

[Rich]

The limiting factor was the lab thermometer that I had on hand topped out at 100 degrees C. As I did the work on the kitchen stove using a cooking pot, I was not interested in using a toxic bath. This info was included in my original posting.

[Rich]

Originally Posted by turbocruiser

Get an accurate aftermarket gauge where you really can read the very wide range of temperatures and the very wide range of situations that cause those temperatures and you will completely change your mind on that thought. Until then you are just guessing, and guess what, you are guessing wrong! Besides, your gauge IS NOT linear now so you only have condition 1 above; by the time you get to condition 4 on your gauge it is likely too late.

I'm not sure why you are telling me that the factory guage lies. I posted that info on this site a long time ago.

I have towed using a full size truck over 50K miles running around 15k gross combined weight with a factory, non degreed coolant temp gauge, and aftermarket degreed engine oil and transmission fluid temp gauges. The engine was a Ford 460 putting out a lot more heat than a cruiser 4.5.

Once I understood what was normal for any of the temp gauges, all that mattered was is it running normal, or slightly hotter than normal, or are the temps hotter than normal and still rising, or are things out of hand and need to stop now. That is the reality of the situation. A few degrees either way is not really that important as to whether or not any remedial action needs to be taken. It is the relative trends and or the extremes that dictate if further action is required.

So, given I have already had the experience, it is safe to say that I won't be changing my mind.

[LandCruiserPhil]

Originally Posted by Rich

I'm not sure why you are telling me that the factory guage lies. I posted that info on this site a long time ago.

I have towed using a full size truck over 50K miles running around 15k gross combined weight with a factory, non degreed coolant temp gauge, and aftermarket degreed engine oil and transmission fluid temp gauges. The engine was a Ford 460 putting out a lot more heat than a cruiser 4.5.

Once I understood what was normal for any of the temp gauges, all that mattered was is it running normal, or slightly hotter than normal, or are the temps hotter than normal and still rising, or are things out of hand and need to stop now. That is the reality of the situation. A few degrees either way is not really that important as to whether or not any remedial action needs to be taken. It is the relative trends and or the extremes that dictate if further action is required.

So, given I have already had the experience, it is safe to say that I won't be changing my mind.

Rich Respectfully I think you are missing it.
I also have a F450 with a 460 the main difference in the two gauges is that when the Ford changes 30 degrees the gauge moves the LC does not.

[Rich]

Oh, no, I am not missing it. I posted info on the flat spot in the cruiser gauge a long long time ago on this website. I may have even been the first to do so. That is why I also went to the trouble to first measure and post the temp resistence curve for the cruiser temp sensor.

I think the factory land cruiser gauge is totally bogus.

The same gauge, behaving in a linear fashion, would suit me just fine.

Getting back to the 460, in a Clubwagon van, when towing in very hot weather under very heavy loads, I.E. 15K lbs, highway, steep grades, hot summer day, all at the same time, it was the engine oil temp that was of more concern than coolant temp. Like the cruiser, the Ford was equipped with two tranny coolers and one engine oil cooler.

[turbocruiser]

Whoaaa, Cool Down Rich, You are approaching your own condition # 4 as you referred above. I'm not trying to offend you any at all man, I'm just sharing my perspective on a problem we are both acknowledging in different ways and with different solutions. I'm sincerely sorry if my perspective was wrongly worded any at all, again, only on open conversation on my part.

[Rich]

I'm not offended at all. Just explaining that what I post is indeed based on my experience. Generally, if I post conjecture, I will say so in the post. Not feeling hot either. Just plain talk. No worries!

[semlin]

Originally Posted by Rich

I don't think extreme precision is required from the coolant temp gauge. Here is all I really need to know 1) is the engine warmed up and running at normal operating temp, 2) is it running hotter than normal, but at a fixed temp and not increasing, 3) is it running hotter than normal and continuing to increase, approaching too hot, and 4) is it running too hot.

The factory gauge omits displaying category 2 and 3 info listed above. If the display were more linear, even without degree markings, I would have all the info I need. I would do a one time calibration to determine where "too hot" begins on the gauge.

i agree with rich, alhtough some calibration would be nice so the "red" is indeed red and I have an idea what temp a few points on the gauge are. It is really kind of annoying to have two temp gauges. I will do it if I have to, but I think what raventai and co. are doing here is the best solution. I even plan to fix my "d" light when I install the mod.

[RavenTai]

Bill, nice big shop, is that a hydraulic tubing bender and big blast cabinet I see?

I think I am going to go with your original chart for now, it is somewhat close to the newest one. Although the newer one gives across the board lower resistance the curve is similar enough. And since we are working with theatrical gauges right now anyway it should be close enough.

main reason being the original corroborates CDans statement that the beginning of the flat spot is around 140F, after a lot of assumptions about this circuit on my part that makes for the beginning of the balance point of the circuit at 75 ohms on the thermistor, your original chart puts it at 135F for 75 ohms witch is very close, also that chart is very wide with temps from 60 F to 270 F making it useful for calculations.


That adds another piece to the puzzle, with the zener diode removed and using the original 75 ohm R1 resistor the gauge would center @ 140 F and travel towards hot from there, the value of the resistor R1 will have to be brought down. Possibly somewhere around 15 -25 ohms.


I think for my testing of the gauge I will get a cheap electric hot plate, they are generally weak and may be more controllable than a propane stove, I think I will heat a pot full of ATF (cheap low viscosity oil), the added mass should slow things down some also, agitation would be best to mix cooler and warmer layers of oil but not sure how to easily do that besides the occasional stir, I like the idea of the plywood, it makes a place to mount everything and keeps heat in witch should help accuracy. Wood also does not conduct much heat nor electricity.

I was originally thinking of trying to use 50/50 mix of coolant and distilled water as it is the medium it will use when installed in the engine, also coolant would circulate and conduct heat better than oil but its boiling point at one atmosphere is between 223 to 227 F depending on who you listen to. And somewhat less at my 900 foot elevation. not high enough to put the gauge though its paces, I cannot think of an easy method for raising its pressure and still getting the sender in there, a pressurized vessel full of hot liquid and a cobbled together garage test just does not sound safe. Also coolant will change concentration over the testing period as the water evaporates


.


In the FSM:

2. INSPECT RADIATOR CAP
………..Using a radiator cap tester, pump the tester and measure the
relief valve opening pressure.
Standard opening pressure:
74 – 103 kPa (0.75 – 1.05 kgf/cm2, 10.7 – 14.9 psi)
Minimum opening pressure:
59 kPa (0.6 kgf/cm2, 8.5 psi)
HINT:
Use the tester’s maximum reading as the opening pressure.
If the opening pressure is less than minimum, replace the radiator
cap.

so average is 12.8 PSI, at that pressure 50/50 coolant boils at…..umm I don’t know, but it is less than 265 F that it boils at under 15 PSI of pressure, so the max I would even think about looking at is somewhere around ~ 260 F as the sender will not read coolant temperatures past that because the coolant will be gone.

Also depending on what chart you look at the sender is getting less and less sensitive as temperature increases resistance is in the single digits.

“Basically, from 175-200 F the temp changes 2 degrees per ohm. 200-210 3 degrees per ohm. 210-220 4 degrees per ohm. 220-230 5 degrees per ohm. 230-245 6. 245-260 7. From 28 ohms at 175F to 5 ohms at 260F “

Originally Posted by cary

Concerning the range of the guage, I would say a wide range. This would keep the guage from bouncing like a pogo stick every time you speed up or slow down, but would show when the motor starts to heat up.

Originally Posted by semlin

great work guys, this is fun to read...

concerning the average temp, I suspect that will fluctuate somewhat between trucks. So many possible variables in the vehicle to affect temp and so many miles on them. I would suggest instead targeting the standard thermostat opening temp at say 1/3 or 1/4 of the dial.

I vote for a wide range that would include all possible operating temps. I think that once we have the flat spot eliminated, a wide range will have enough sensitivity for what we need. A significant gauge bounce every time you went up a hill or stopped at a traffic light would be distracting.

Maybe I am being overly optimistic here but I am hoping that Toyota has used good materials in this gauge that would be fairly consistent over years of use, the Wheatstone bridge circuit itself is very accurate and not bothered by problems such as fluctuating source voltage like other circuits. The air core motor also within reason does not wear out, it has a permanent magnet rotor, even major degradation of the magnet would not affect reading until it did not have the strength to move the needle. The stators are just windings of copper wire, as long as there is a continuous connection and no shorts between winds they will produce a consistent field for any given amperage. As long as all the components are in good shape it should be reasonably repeatable truck to truck, I have no idea’s on year differences yet but have not seen any indication that they are different yet so for now will assume they are the same.

For fluctuating temperatures if they are fluctuating personally I would like to see that, I would think (probably optimism again) that as I cruise down the highway at a consistent speed on flat or on the gently rolling hills around here the temperature would be fairly constant.

Originally Posted by Gauge

Actually I don't mind watching the gauge rise when I am climbing a hill and go down when I am descending - at least I know that my gauge is working. And if my engine gets hot, even if it is for a short time, I don't mind knowing that.

Cary Semlin and Gauge, any chance putting #’s to those ranges? Maybe we are thinking more alike than we think. One though I had was making the middle the normal operating temp (still don’t know exactly what that is but it is around 200 F) and perhaps the bottom of the red area be around 226, that # was sinifigant to Toyota for some reason as that is where the AC kicks off at. total WAG but that would give 245 or better where the gauge pegs up over the “H”, does anybody want to know any more than 245 F? For me no I need to shut down before then. This would not show much of the warm up, another WAG maybe first movement off cold at 155F, again anything below that is just “not close to operating temp yet” to me in a northern climate I could see where you may want to see more because there is “not warmed up yet” and below that “really not warmed up yet”


Anyway any #’s helpful, what average operating temp is being seen and also what temperatures you would like to be able to see.


The Miata mod includes several different ranges people can select for their mod, maybe I can do that also

Turbocruiser, no offence taken, discussion gets to the bottom of things. Boils them down to truths. I see some of what you are saying, a marked wide range gauge is quite very nice. It Gives real #’s to work with almost down to the degree, but a modified stock gauge is enough to tell me enough about engine temperature to make decision on its operation. With testing of the circuit both “on the stove” and in the truck with comparison to OBD2 readings translations of needle position to temperature can be made. This is all I want and is good enough for me. I would say that I do want to do this.

Originally Posted by Rookie2

Awesome. Got one on the way. This is perfect, learn a little about electronics, and have another resource for enhancing the GA knowledge.


Rookie2

I forgot besides being an engineer you are also a private pilot, I hope you like : )

Once we have a working gauge, It would also be great to have an overlay sticker to apply directly to the gauge face (not the bezel) with a few data points. That seems like a job for a graphic design person to come up with something that looked reasonably oem.

Another thought I have had on the LED alarm issue is that the turbo diesel 80's have an LED light in the tachometer instrument face to indicate when the turbo is on. The tach is otherwise identical so I wonder if the 80 gas series tachs might already have a ready made mounting point and punchout hole for an LED that could be drilled to allow for this as a temp alarm.

I’ll look next time I am in the cluster. I am pretty sure the face card of the temp gauge could be drilled to accommodate an LED, or better yet just back light the gauge red, it does pass light in the white areas. Might be a little dim in the day. I am wondering if an LED could be integrated into the gauge without needing a switch, possibly even using the removed zener diode as the trigger. Tapping another device in the circuit would change its readings some, the smaller the current the less change. Hmmm getting more complicated.



This is getting long, Going to need a recap soon.