Adding coolant temp gauge?

[RavenTai]

I think I'm a better driver now that the newness of the guage has worn off. Very little change in the needles position for more that 5k miles now.

hmm, That is odd, neither you nor Rook2 seam to get much variation, I have some spikes at logical times, not near an overheat (just under 205F was the highest) but quite noticeable needle movement.

I am wondering if these small spikes are nomral or if I have a cooling problem?

fan clutch, T-stat, coolant, and belts are all less than 2 years old and OEM. due for coolant change soon but dotn think that is it. my rad has almost no sludge.

 

[landtank]

RT I do mostly highway driving so I doubt that there would be noticable spikes. How much movement are you calling a spike?

 

[RavenTai]

well here are some pics, workign form memory here, earlier before it got cold the temp would climb up some any time at idle, with the AC on it was worse, highest was in a backed up fast food drive through about 85 F AC on, got to about 203 or so before I reved the engine to get the temp back down.

even now in the cooler weather in traffic at low speed I can get bumps up to 198 or so

here are pics of 203 and 198 from the test bed, really need to get arround to making that vid from the stills.

 

[Rookie2]

If middle is 189 and bottom of red is 217, sounds like it's moving pretty good... several needle widths.

Interesting. My driving has been mostly short trips and around town. I have to really be watching to see slight variations in the needle movement.

Maybe it's that Hotlanta heat .

 

[RavenTai]

so if I am gettign 203 or so in 85 degree weather what was the temperature doing last august in 100 degree weather?

 

[RavenTai]

If middle is 189 and bottom of red is 217, sounds like it's moving pretty good... several needle widths.

Interesting. My driving has been mostly short trips and around town. I have to really be watching to see slight variations in the needle movement.

Maybe it's that Hotlanta heat .

could it is warmer here and the traffic sucks, I may have to wait until it warms up for you guys bvefore I get any info, most of the time I spend on the freeway and it stays nice and centered, it is idle and light to light traffic that gets it.

 

[Rookie2]

I think so. You're driving definitely sounds more severe than mine. Even my around town driving doesn't have alot of what I consider stop and go. I haven't observed it yet with the AC running, so that's another difference. It's generally been pretty cold out since I did modified my guage except one day we had a spike in outside temp (maybe upper 60's to lower 70's) was the only time I've seen any perceptible movement in the guage.

 

[Darwood]

I've tried to read through this whole thread, but I still don't understand why the values that were chosen were chosen. Can someone explain it to me why the bottom of the red is 217? Would a larger resistor replacing the zenor diode raise the temp for the red zone? I really should dust off my EE books and try to figure out the math.

 

[RavenTai]

I've tried to read through this whole thread, but I still don't understand why the values that were chosen were chosen. Can someone explain it to me why the bottom of the red is 217? Would a larger resistor replacing the zenor diode raise the temp for the red zone? I really should dust off my EE books and try to figure out the math.

Reading this entire thread in one sitting is no easy task.

The reason for the scale is based on what we know of Toyota’s ideas for the limits of engine temps.

I take it you do not like it?

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.

Center is the regular operating temp that the cooling sytem tries for when it can,
Top of red is AC cutout, bottom of red is AC return
Toyota thought that 226°F was hot enough to make the passengers uncomfortable in favor of saving the engine, considering that is 42°F over the thermostat opening, and 23°F over full open temp that is defiantly an overheat, 217°F is where the AC should be returned, that red band is as close as I could get it to that. The gauge will still read up to 244°F I did not think it was useful to read beyond that temp,


Yes raising the value of the diode replacement resistor would widen the range, moving the cold line cooler and the hot line hotter, but I would not recommend it, I rather like the scale where it is now, it seams to fit well temperature based events well. Also you will loose all calibration and have no info on what the needle position is saying.

Raven

 

[Darwood]

Reading this entire thread in one sitting is no easy task.

The reason for the scale is based on what we know of Toyota’s ideas for the limits of engine temps.

I take it you do not like it?

No, it's not that I don't like it. It's more that I don't have a frame of reference to go off of, since I don't have much experience of what temperature is ok for a cooling system and which temperature isn't.

Center is the regular operating temp that the cooling sytem tries for when it can,
Top of red is AC cutout, bottom of red is AC return
Toyota thought that 226°F was hot enough to make the passengers uncomfortable in favor of saving the engine, considering that is 42°F over the thermostat opening, and 23°F over full open temp that is defiantly an overheat, 217°F is where the AC should be returned, that red band is as close as I could get it to that. The gauge will still read up to 244°F I did not think it was useful to read beyond that temp,

This makes sense, however in my mind it might make a little more sense to make the bottom of the red 226 since this seems to be the danger zone. The bottom of the red to me means that I need to pull over. The 217 temp seems to be the safety zone before the A/C is turned back on, which to me means that "we aren't going to turn the A/C back on until you are a good distance below the danger zone." I do remember that all we have to work with is a couple of resistors and I don't remember the feasibility of this.

Yes raising the value of the diode replacement resistor would widen the range, moving the cold line cooler and the hot line hotter, but I would not recommend it, I rather like the scale where it is now, it seams to fit well temperature based events well. Also you will loose all calibration and have no info on what the needle position is saying.

Raven

Thank you for confirming my suspicion. Do you know if the OBDII sensor for temperature is the same one that the gauge uses?

Once again thanks Raven for your hard work on this. Just about anything is better than the gauge we did have.

 

[Rookie2]

I see you're point, but I think it's kind of nickel and diming. More than anything, to me it's a matter of knowing what the engine temps are doing (which this mod achieves). When it gets to the bottom of the red, you know you need to be keeping an eye on it, when it gets to the top of the red, you've entered the danger zone.

Just about anything is better than the gauge we did have.

I'm sure you didn't mean anything by it, but this probably could of been worded a little differently .

 

[Darwood]

I see you're point, but I think it's kind of nickel and diming. More than anything, to me it's a matter of knowing what the engine temps are doing (which this mod achieves). When it gets to the bottom of the red, you know you need to be keeping an eye on it, when it gets to the top of the red, you've entered the danger zone.

Oh yes I agree it is nickle and diming.

I'm sure you didn't mean anything by it, but this probably could of been worded a little differently .

Yes I see what you mean. I did not intend it to be taken that way. What I ment to say is "Thanks for the mod and just getting it to move would have been good enough"

 

[RavenTai]

In development I was originally thinking about a 226 bottom of red, after working on it for a wile I went a little more conservative, so far seams about right to me and I am happy with it.

I have not seen a reading over 205 or so and it worries me at that level, I would think 217 would be quite out of the ordinary and worth my attention. ( I personally would take action before that point)

The OBDII readable sensor is separate,
On the foreword left side of the head above the oil filter there are 3 temp sensors, in no particular order:
One is a an on/off thermal switch for the AC (226/217) cut off
Another is a thermistor for the cluster gauge.
The last the thermistor for the ECU, this is the one you can read with OBDII

These three are completely independent from each other.


Could you tell me more abotu what you are getting? are you hitting the 217 mark?

 

[Darwood]

Could you tell me more abotu what you are getting? are you hitting the 217 mark?

I've only driven the truck a couple times since I modded the gauge. My wife has mainly been driving the truck and well, she's not the best at giving data points. The highest I've seen it is at the 3/4 mark which according to the pics should be around 205? This was just cruising on the highway at 80 as I stated in the other thread.

I'm curious to see how the gauge reacts when we go to Death Valley in March. It should see a lot of ambient temperature change then which should give some interesting data points.

 

[cpg]

RT I notice the same movement you do. Higway in the middle, load closer to red, coasting down hill under middle.

 

[Darwood]

Ok I've now spent the past couple days at work refreshing up on Thevenin equivalents and I think I have the math working right. Yay I have my freshman understanding of electronics back.

Thanks again RavenTai for your research and numbers. Also thanks for the gif showing the stock gauge. As requested here is a link to the gif for everyone.

http://web.mac.com/darwood/Pictures/Temp/aptemp2O.gif

I did some math on the 110 degree resistor with a wire replacing the zener diode (assuming that L1 = 95.3 ohms, L2 = 81.5 ohms, and L3 = 46.0 ohms) and I got .9140 volts across L1 at 226 degree F. This is using a resistor value of 38.4 ohms for R2. This should put the needle at above the red zone. I've read the actual results you obtained and it seems like this is about 10 degrees off (not unlike the value for the 110 ohm resistor). In reality .9140 volts across L1 with R1 = 110 ohms and a short for the diode is about 217 degree F.

A coworker of mine mentioned that since the needle is pegged cold with a spring of some sort that this could be why the temps are lower than we expect given the resistances. The spring is biasing the sweep a bit. This may or may not be true. I think to figure out if it is we would have to divulge into the realm of differential equations (which I'm currently not up to).

I'm going to be playing with resistor values to replace the diode today to see what I get and to see how closely the math mimics reality.

RavenTai as a request, if you do any more tests can you always measure the voltage across L1? That would be awsome. To me that value is the best way to see if the math on paper matches reality. Source voltage is nice to know but seeing that it doesn't change much it isn't that valuable.

 

[Darwood]

RavenTai as a request, if you do any more tests can you always measure the voltage across L1? That would be awsome. To me that value is the best way to see if the math on paper matches reality. Source voltage is nice to know but seeing that it doesn't change much it isn't that valuable.

Ok I'm stupid. In the gif you have the voltages will always be the same vs the needle movement. In other words the voltage across L1 will always have the same result regardless of change in resistance so there is no need to find these values again, unless it is to verify them.



Though it would also still help with the whole voltage vs temp vs needle movement reference thing.

 

[Darwood]

Though it would also still help with the whole voltage vs temp vs needle movement reference thing.

The more I do the math the more I would like more readings in regards to the voltage over L1 and the temperature. Right now I'm not trusting my calculations to calibrate the thermistor graph due to not being 100 percent sure on how to handle the diode in the circuit when it comes to Thevenin equivalents. As noticed in real life the temperatures and the resistances measured from the thermistor aren't exact when it comes to the circuit. The 110 ohm resistor should have created a center of 200 degrees but it seems like it was off 9 to 10 degrees. It looks like the curve is a bit off when the circuit is involved.

I did some calculations on one of the gif images and for a voltage of .200 volts across L1 I calculated that the resistor R2 should be 31.9 ohms (or 30.8 ohms depending on how I calculate it ). This corresponds to 228 degrees Fahrenheit based on the gif.

If you look at the chart 31 ohms should be between 239 and 240 degrees.

I also have some calculations on the current circuit with the 110 ohm R1 resistor and various diode replacements.

These are the numbers I get for the R2 resistance when the voltage across L1 is .740 volts which should put the needle at the bottom of the red zone (i.e. the bottom of the needle is touching the bottom edge of the red zone):

D1: 100 ohms R2: 32.9 ohms
D1: 75 ohms R2: 34.5 ohms
D1: 50 ohms R2: 36.9 ohms
D1: 90 ohms R2: 33.0 ohms

I also thought some about a replacement zener diode but the smallest break over I could find in the Mouser catalogue was 2.4 volts which is larger than the 2 volt break over of the stock component. I'm guessing a 1 volt break over would shrink the dead zone to only 20 degrees but I haven't calculated that nor is there much point if we can't find a diode to meet that requirement. Also with a diode the resolution would be harder to modify.

 

[RavenTai]

Darwood hold tight, I'll post up some more tonight,

I had a lot of trouble getting an accurate model of the gauge, I wound up gettign a basic model of it and then fine tuning by trial and error. if we have a good enough model that takes all the varriables into consideration then these kinds of things can be done but I could not do it, it sounds like you are getting further on that though.

I would not bother with trying to calacualate with the diode in place, it adds another layer of complication on top of many

 

[Darwood]

Darwood hold tight, I'll post up some more tonight,

I had a lot of trouble getting an accurate model of the gauge, I wound up gettign a basic model of it and then fine tuning by trial and error. if we have a good enough model that takes all the varriables into consideration then these kinds of things can be done but I could not do it, it sounds like you are getting further on that though.

I would not bother with trying to calacualate with the diode in place, it adds another layer of complication on top of many

More data is good

The model you came up with seems to work really well. The model might not be perfect but it's close. As I mentioned if we can tweak the resistance vs temperature a little I think we can get it pretty accurate. The inductors are probably to blame for the discrepancies.

If at all possible I would like to get rid of the diode in the calculations. Hopefully you have what I need to do it. As far as the diode goes if I assume a .7 volt drop across it the math seems to work out. In one calculation I was able to determine that the dead zone started (i.e. when zero volts across L1 first occurs) when the R2 resistor fell to 74.895 ohms. Comparing to the graph this gives up 187 degree Fahrenheit. Looking at the gif it looks like this is around 185 to 187 which is encouraging.