Adding coolant temp gauge?

[semlin]

Raventai

Great work. Your results seem to be correct and it looks like there may be a major difference between 93/94 and 95-97 gauge flatspots. Landtank had the AC cut out on his 97 (226 degrees) with the gauge still looking normal. https://forum.ih8mud.com/showthread.php?t=20424&highlight=a/c+cutoff (post #6)

If I read you right then the gauge on a 95-97 is steady at 170 to 230 when it first moves and 260 when it first hits red?

Dan's 1993 was steady at 140 to 215/8 degrees on his truck, and was only at 223/5 at 3/4 on the gauge dial. I don't think any mod to Dan's truck including the low t-stat would impact on his gauge response. Perhaps his Isspro gauge is calibrated low or is in a location where it sees lower temps but I doubt either could explain that kind of swing.

I also notice the "dead" range is different. Dan has a 75 degree range, while you are finding a 60 degree range, so this would also support a different gauge response unless I am forgetting ohms law or something.

If all this is right then maybe that's why later models tend to blow head gaskets more often since you are in big trouble if the gauge ever moves at all .

If the gauges are different then it may be a crapshoot whether the same mod will work for both gauges but it may just be a matter of a different diode and resister on two identical parts, in which case we might be in luck.

 

[cruiserdan]

I have recently switched back to a stocker thermostat. My gauge reads the same in relation to the dead-spot. What I have noticed is that my Isspro must be pretty close to on because the new stat gets the motor up to 190 and won't let it drop below about 188 or so even on a log downhill coast. That is consistant with what is suppsed to be a "190 degree" thermostat. The 190 starts to open a bit below 190 which would explain why I can get it to fudge to just under that on a long coast. The 160 TRD stat would let the motor cool off to as low as 170 or so in the same situation.

As Photoman observed some time back the only thing a lower thermostat will do for you is increase the time window before you over-heat, it won't do a damn thing about over-heating.

D-

 

[e9999]

I have recently switched back to a stocker thermostat. My gauge reads the same in relation to the dead-spot. What I have noticed is that my Isspro must be pretty close to on because the new stat gets the motor up to 190 and won't let it drop below about 188 or so even on a log downhill coast. That is consistant with what is suppsed to be a "190 degree" thermostat. The 190 starts to open a bit below 190 which would explain why I can get it to fudge to just under that on a long coast. The 160 TRD stat would let the motor cool off to as low as 170 or so in the same situation.

As Photoman observed some time back the only thing a lower thermostat will do for you is increase the time window before you over-heat, it won't do a damn thing about over-heating.

D-

190 is stock? mine is lower IIRC, more like 180

add: (numbers here: https://forum.ih8mud.com/showthread.php?t=53209 on coolant temps)

 

[semlin]

a couple of other questions

-by "centred" do you mean the standard temp position that looks to be just below centre on the gauge when driving? Is this the true centre?

-if so, that means with a 75 watt resister there is 30 degrees F of swing between standard position and the beginning of red?

-am i also correct that the gauge response is linear? If so, at what temperature does the gauge first move, because I assume that 170 minus that number gives 50% of the full "range" of swing (or did you alreayd test how hot it would go before you buried the needle?)

-does that amount of swing remain fixed no matter what resister you use?

-if so, I would vote for 195 as the centre position which would yield 225 as the bottom of the red. If it is hot enough to shut down the AC that is hot enough to point at the red line. that would still leave you with what looks like 10-15 degrees of further gauge response to the top of the red. I also see no need for a replacement zenon diode to numb out any part of the temp response.

-if you can vary the swing I would suggest you decrease it a little to give a broader "red range" between overheating and the needle buried.

 

[semlin]

190 is stock? mine is lower IIRC, more like 180

add: (numbers here: https://forum.ih8mud.com/showthread.php?t=53209 on coolant temps)

These results also confirm the 97 gauge is dead until at least 220. I think we should assume 230 is correct.

 

[RavenTai]

Cary

1. Yes the flat spot is caused by the Zener diode. we will be removing it and I think replacing it with a resistor, you could replace it with just a wire and have still have a linear gauge, I was originally thinking this would lead to too small of a range but running the #'s just a wire might be about right.

That would be too easy


2. R2 you got it , one addition, the forward volt drop is a thing of all diodes, in order to perform their electronic check valve function they take a tax of dropping a certain voltage, silicon and germanium diodes drop different amounts but I cant remember witch is witch. Maybe .7v is silicon?

3. I have briefly considered this but I think I want to see all changes/trends however small. It could be done though I am not sure it would be as tight as you are looking for, we already have a forward volt drop that cannot be gotten around and adds to the reverse volt drop, so even a very low value Zener Diode might have a considerable dead zone. I will try to figure that one out at least on paper

Raventai

Great work. Your results seem to be correct and it looks like there may be a major difference between 93/94 and 95-97 gauge flatspots. Landtank had the AC cut out on his 97 (226 degrees) with the gauge still looking normal. https://forum.ih8mud.com/showthread.php?t=20424&highlight=a/c+cutoff (post #6)

Good to know, I was worried about the difference, but I am not going to call the results 100% accurate just yet because of the voltage.

If I read you right then the gauge on a 95-97 is steady at 170 to 230 when it first moves and 260 when it first hits red?

Yep, also 145F° was just above the cold line,

Dan's 1993 was steady at 140 to 215/8 degrees on his truck, and was only at 223/5 at 3/4 on the gauge dial. I don't think any mod to Dan's truck including the low t-stat would impact on his gauge response. Perhaps his Isspro gauge is calibrated low or is in a location where it sees lower temps but I doubt either could explain that kind of swing.

I also notice the "dead" range is different. Dan has a 75 degree range, while you are finding a 60 degree range, so this would also support a different gauge response unless I am forgetting ohms law or something.

Yep Dans readings of gauge vs gauge are still valid, only thing that is not comparable to stockers is what temperature he is running.

I am defining the dead band by watching the voltage across the windings, finding the dead band by watching the needle (waiting to actual movement instead of start of voltage change) may be enough explanation of the 15° difference in range but not the different temps the range happen at.

If all this is right then maybe that's why later models tend to blow head gaskets more often since you are in big trouble if the gauge ever moves at all .

If the gauges are different then it may be a crapshoot whether the same mod will work for both gauges but it may just be a matter of a different diode and resister on two identical parts, in which case we might be in luck.

After we get the mod someone will need to open up a 93/94 and see what is there, the thermistor is the same, if the air core motor is the same then the mod will still work. As the rest will be replaced.

 

[RavenTai]

Thanks for the linkls definatly want to center @ 200

 

[cruiserdan]

190 is stock? mine is lower IIRC, more like 180

OK, here is what the book says, perhaps 190 may not be completely accurate I don't know.

The stock stat is stamped 82 (which is 179.6 F). The TRD stat is stamped 71 (which is 159.8 F). The FSM states that the opening temperature of the stock stat is 80-84 C (176-183.2 F) and that the "valve lift" is 10 mm or more at 95 C (203 F).

I wish I could find published hard numbers for the "normal" operating range of these engines. I have yet to find that. Reading between the lines you find such things as the A/C cut-out at 226 F and the cut-in at 217 F. Based on info such as that I assume that the top end of "normal" is around where the A/C will come back on.

 

[RavenTai]

a couple of other questions

-by "centred" do you mean the standard temp position that looks to be just below centre on the gauge when driving? Is this the true centre?

It is interesting you mention this, the gauge in my 96 LX “centers” dead middle of the gauge wile driving, the test gauge appears to be maybe half a needle width low when centered, may be parallax error as the needle is pretty high off the card. But no matter center is easy to find electrically, it is when there is no current in the inductor L1 shown in the schematics in post # 58, when there is no current passing through L1 there is no volt drop across it and the needle centers. This would be whatever position you see when normally driving after warm up but before overheat.

-if so, that means with a 75 watt resister there is 30 degrees F of swing between standard position and the beginning of red?

-am i also correct that the gauge response is linear? If so, at what temperature does the gauge first move, because I assume that 170 minus that number gives 50% of the full "range" of swing (or did you alreayd test how hot it would go before you buried the needle?)

-does that amount of swing remain fixed no matter what resister you use?

Well first off after removing the diode there are two adjusts that can be made,

The 75 ohm resistor does not effect swing per say, this resistor affects the balance point or basically at what temperature the gauge “centers”.. The 75 ohm resistor and the thermistor create a variable voltage between them. These two resistors form the raw data of temperature. The rest of the circuit reads and displays this data. One thing to note, we will not lower the value of the 75 ohm resistor, only raise it. The lower the resistance of this pair the higher the current, already when reading higher temperatures the 75 ohm resistor gets quite hot, have no idea how much overhead there is for higher current in the circuit so only safe path is equal or lower current than stock. Fortunately going to a higher resistance move the center temperature lower, I don’t think anybody wants center higher than 212 so we are in luck.

Also may have found a way to tell if a truck has ever been overheated, more on that later.

The second adjustment is the resistor that replaces the diode, this adjusts how sensitive the needle is, lower resistance make for more needle swing per degree or a tighter range, higher resistance less swing per degree or a wider range.

So the gauge is completely adjustable within limits.

The variable voltage produced between the 75 ohm resistor and the thermistor is linear up to about 245°
Where it starts leveling off.

I guess eventually response would end but that point is above the boiling point of coolant so no worries. I do not know if the gauge will response will be linear or not as I was mainly watching the circuit electrically on the first cook, but for now it looks promising. It is harder to accurately measure needle movement than temperature and voltage. I think photography will help here, need to change up the test bed some.

-if so, I would vote for 195 as the centre position which would yield 225 as the bottom of the red. If it is hot enough to shut down the AC that is hot enough to point at the red line. that would still leave you with what looks like 10-15 degrees of further gauge response to the top of the red. I also see no need for a replacement zenon diode to numb out any part of the temp response.

-if you can vary the swing I would suggest you decrease it a little to give a broader "red range" between overheating and the needle buried.

195 center might be a little low. From what I can gather a system in good shape can go up to 200 on a hot day and still be considered normal, I would like all of the top half to be in the above normal range. If a lot of people see their gauge as just below center then 195 might be better.

225/226 sounds good, needle buried will still be in the pissing HG/exploding radiator range. No need to see above boiling coolant temps just loosing resolution you cannot use.

 

[semlin]

mine is definitely a tad below centre and that's the way I've always heard it described. It could be the combination of the angle I am looking at it when driving and the distortion caused by the raised needle from the gauge.

that raises the interesting question of whether what you see as the red line in the test is the same as it will appear in the dash. I think you may want to verify your observations from a simulated driver's eye view, although that would, if anything, mean you have so far understated the temperature at which you hit red!!

if you can vary the swing then I am ok with a 200 degree centre point. I was worried that would yield a 230 degree red line which is too high imho. If you can tweak it with enough precision to ensure 225 or so is the red line then 200 is fine.

We talked about making an overlay for the gauge card with a couple more increments. it looks like it would be impossible to remove the needle so as to accurately scan the gauge so we will need to figure out what the radius is of the circle. with that info I can try to get started on putting together the overlay. If I know what the target swing and centre point will be then I can aim for a mark at say 217 degrees for a yellow line, and 200 for a white line.

I am also going to start looking around for a 93-94 gauge.

 

[Rich]

...It is harder to accurately measure needle movement than temperature and voltage...

Create a paper template with a radial graph. Tape to gauge behind the needle. Video tape the gauge and temp readout simultaneously while under test.

BTW, use cooking oil to avoid the nasty smell. Toss in some taters if you get hungry.

 

[landtank]

This stuff looks great. It's funny how sensitive the oil pressure guage seems and the temp just flat lines. I'm with Semlin here as far as what how I'd like my guage to work. That is near centered when normal and red lined at AC cut out. That way I could turn off the AC if I started to climb near that point ahead of time.

As far as the viewing angle, it will all be different for all of us and just something we will need to adjust to after the change.

Nice work!!!

 

[RavenTai]

Semlin, I have been reading the gauge by trying to square off on the needle base. It has vertical sides to sight down; I think that will have to be our datum line for viewing angle and each driver can adjust from there. I am hoping to set up the test bed so the gauge can stay stationary (as it sits now I need access to the back side to take measurements) and take photos from a tripod with the DMM and digital thermometer in view, that should solve viewing angle and provide angle measurements, also the voltage/angle/temperature readings will be taken at the exact same moment instead of a slight delay when done by hand

After I am done with everything I will look into taking the gauge apart to see how hard it would be to apply an overlay. Don’t want to do that until I have all testing complete.

I can come up with different ranges but I am only going to test one in my truck, if you chosse one of the others you will be the guinea pig for that setting.

Had some time today and did a second cook, this time the diode was bypassed using the ammeter of my DMM, this is not ideal as an ammeter has some resistance but I am hesitant to modify the gauge until I get the test bed right and get a all the info I can out f the gauge as it sits stock. I have some ideas and parts on order to this end.

Making a Wheatstone bridge using the gauge winding the way Toyota did has a side effect, it is source voltage sensitive, and a true whetstone bridge is not. Higher source voltage makes the range slightly wider, the center points stays the same though.

I found my battery charger but did not have enough time to get the voltage up to 14.x where it should be for accurate testing but here are some early rough returns, source voltage was increasing the entire time so these #’s will not be repeatable.

Pegged “C” 180
Cold line 190
Center 210-215 (DMM was busy so had find get center by eye)
Bottom of red 240
Top of red 247
Pegged on the “H” 255

I don’t think that will quite work for anybody but it would be simple to do just solder in one wire. If I were to shift that whole scale down about 13 degrees I would be happy with that. It would be simple, one resistor and one wire to solder in.

The total sweep of the needle is just under 90 degrees (angle degrees) and 75 temperature degrees, this is almost the maximum resolution, and it can only go down from here.

One other thing that is bugging me is what makes the needle peg to C when the power is removed? There has to be a small spring or magnet in the air core motor somewhere.

I will have most of a day Tuesday to work on this and should make good progress.

Rich I should have used cooking oil, I though about it but all I had around was extra virgin olive oil to expensive to fill a pot with. I should have bought some cheap veggie oil.

This stuff looks great. It's funny how sensitive the oil pressure guage seems and the temp just flat lines. I'm with Semlin here as far as what how I'd like my guage to work. That is near centered when normal and red lined at AC cut out. That way I could turn off the AC if I started to climb near that point ahead of time.

As far as the viewing angle, it will all be different for all of us and just something we will need to adjust to after the change.

Nice work!!!

The Miata guy did something interesting, he gave values for test resistors that temporarily replace the thermistor to test the modified gauge, maybe we can do the same, this will test the mod and also give you an opportunity to see the angles at simulated temperatures.

 

[semlin]

raventai

a 13 degree drop instigated by a single resister sounds good to me too. I guess we need to see how it works at 14 volts but if it's close... I'm there.

one question, and pardon my ignorance asking it as my understanding of electricity is at the level of ben franklin before the kite, so bear with me. you mentioned that the centre or dead point involves no voltage, and you mentioned the resister heats up when reading higher temps because of voltage. you may be talking about different things, but if the gauge is seeing 0v at centre and voltage at other temps, we should be sure all the components can take voltage on a sustained basis without hearing if we use a fully responsive gauge because it is unlikely the gauge will ever be centred for long. I am sure you have thought of this, but just thought I'd mention it because the alternative seems to me to introduce a different diode with say a circa 190-205 dead spot. anyway no need for a detailed explanation if you've got this covered. it's more a comment, as I lost your technical explanataion a while back before we crossed the whetstone bridge .

 

[RavenTai]

From this thread

https://forum.ih8mud.com/showthread.php?t=59453

So far seams like 14.5 is a common voltage so I will try to shoot for that. (Mine was 14.47 I rounded up)


Semlin

Simple answer: talking about two different parts of the circuit. the coil L1 drops 0 volts and passes 0 amps at center, the resistor R1 (75 ohm resistor) drops varying levels voltage and passes of varying levels current at all temperatures.

After mod currents (amperage) will be the same and in some areas less than as stock for a given temperature so we will be safe. Also the 75 ohm resistor (only under built part in this circuit) will be upgraded form stock to better handle the load.

I don’t think this is above anybody here, you all are smart folks in one field or another. It is just that if you have never looked into this stuff it sounds like Greek. I would be glad to try to give a layman’s explanation if you want.


the folowing is probably the best of the schematics to look at for understanding, all of them are electrically the same just diffrent arrangment of the parts for clarity of certian points.

 

[RavenTai]

For Semlin

 

[semlin]

?? i'm hoping there is a PM to go with that or maybe it will make sense when i get there. I'll try to pick it up saturday one way or another.

 

[RavenTai]

"i'm hoping there is a PM to go with that"


There is, just sent sorry for the timing

 

[semlin]

ok raventai I have an official 93 factory temp gauge. unfortunately my digital camera is horrible at close ups. I think you can see enough to ask questions.

in the mean time I'll se about shipping it off to you...

 

[semlin]

using your 1997 gauge photo (attached) as a reference the back panel in virtually identical.. difference are

1. pn# at top is 769902-961 on mine, looks like 769916-920 on yours

2. third kanji script down, the box on the left looks like it has an H or M in the middle where you have two straight vertical lines. otherwise all the exact same script.

3.at the bottom where you have an "IGN" labelled bass nut, I have one of my 4 raised mounting points still labelled "ign". Where you have the post just below, I have nothing and the circuit board copper does not branch out.

4 the two upper mounting posts on mine have round brass bushings unlike the other two posts which have the same hexagonal style as yours.