Adding coolant temp gauge? (1 Viewer)

[RavenTai]

I haven't messed with any of the Toy senders, but all of the other senders I have seen are basic thermistors, or a resistor that changes resistance with temperature. They follow a known Temp/Resistance curve. The dead spot is in the guage. Nearly all new cars do this electrically within the guage so that the driver never sees the needle move if the temp stays within "normal" operating range.

As far as running 2 guages off the same sender goes...

1) thermistors can be designed to have any response curve desired, so the chances are pretty slim that an aftermarket sender would be identical to the stocker, therfor an aftermarket guage would not have the same response curve as a factory unit because the each would be calibrated to their respective senders.

2) if you have a 1-wire sender (never looked at the LC's), the guage is measuring the resistance by the amount of current flowing through the resistor. If you have 2 guages. Each supplies 12V at the guage through the resistor to ground at whichever metal piece the sender is screwed into. A 12V drop accross the resistor will pass exactly X amps and ONLY X amps. Each guage would supply half the current (X/2), therefore each will read half the temp, assuming they are calibrated the same. Could work with a 2 wire sender where the resistance across the resistor is measured directly, like having 2 multimeters across the same curcuit, but all aftermarket guages I have seen run 1-wire senders.

Chris

It is a one wire, the thermistor has one wire leading to it and grounds to the engine or at least in my 96 it is, and from what I have seen yes the flat spot is in the gage not the thermistor/sender. I think it was Rich and Photoman? that plotted the thermistor’s resistance at different temperatures, it is a standard curve with no flat sports, the Miata fix is on the gage, that gage s similar to but not exactly the same as our gage, they are both made by Yazaki Meter.


I have been trying to get a gage to work with, so far no luck but I am still looking.

Am I only the only person who has a problem with installing ANOTHER temperature gauge to replace the OEM gauge that should be working?

You are not the only one but as of right now and for who knows how long the factory gage is almost useless. Something has to be done to get real water temperature readings, either through OBD/software or an aftermarket gage. The former only available to 95ish and up. For Dan’s 93 aftermarket gage is the best path.

There has to be a way to make the OEM gauge more accurate - either by replacing the sending unit or the gauge itself.

I think there is a way to cheaply linearize the OEM gauge with a few resistors and a little of you time same as the Miata, It will not be graduated like an AM gauge but as long as it moves with temperature change it is enough to tell when something abnormal happens

I have zero confidence in the factory Toyota temp gauge and it bothers me that I have no knowledge of the engines true temperature.

Same here.

 

[RavenTai]

Could you post a link to the supra mod?

I have seen the miata mod, both my 96's and the miata gages are made by yazaki meter and they are similar but there are enough differences that the miata mod will not transfer over directly, it would need some tweaking/ testing. As far as I know nobody is working on the mod. I think it was Rich that measured the response of the thermister at different temperatures. I pulled out the gage and took pictures and made a schematic, but AFIK nobody has gone any further with it.

Although my electronic skills are not EE grade I think I am proficient enough to come up with this mod. I am pretty sure there are some other members here with the skills needed the stumbling block is having a loose tamp gage and thermister to work with.

Anybody have a spare 95-97 cluster ( I assume 95-97 are the same/similar enough? ) they could pull the temp gage out of?

The stock gage does not have markings through most of the range so even after mod you would not be able to tell exactly what temperate you are running this makes it somewhat inferior to an aftermarket gage, a fixed stock gage does have one advantage it is already there and well blended into the dash, with a fixed gage you would get needle movement with temperature change and be able to tell when you are approaching an overheat witch is all I really want anyway.


the pics I took were lost when I lost my server so I will repost them here.

originally from thsi thread

https://forum.ih8mud.com/showthread.php?t=27705

^^^^^originally from this thread

https://forum.ih8mud.com/showthread.php?t=50020

was also talked about in this thread

https://forum.ih8mud.com/showthread.php?t=52460

Miata Mod

http://www.gravitydesign.net/saturn/miata/MTGLP.cfm

 

[Gauge]

Engine temperature is a KEY measuring metric for any engine, and in my opinion is much more important than volts, RPM and even speed. Given the susceptibility for these engines to have head gasket failure, you would think that Toyota would at least provide an accurate gauge to help us monitor engine temperatures and prevent breakdowns and engine failure.

I would LOVE to see someone come up with a mod that makes the temperature gauge do what it was designed to do - SHOW ME WHEN MY ENGINE IS GETTING HOT.

 

[Rookie2]

Thanks for the picture ClownMidget.

I think it was Rich and Photoman? that plotted the thermistor’s resistance at different temperatures, it is a standard curve with no flat sports

FWIW, the FSM has the resistance-temparture curve for the temp. sensor. It's logrithmic, with no flat spots.

I recall reading in some previous threads that the temp. gauge was not always like this, but it was changed due to all the soccer moms coming into the dealership thinking their vehicles were overheating because the gauge was read near or at high.

So in my thinking, if Toyota decided to make a change, the logical place to do that would be at the gauge. My guess is that something was added to the circuit board at the gauge, that filters or maintains a similar resistance over a given temperature ranges. But I'm no EE either .


Rookie2

 

[semlin]

hmmm, maybe we don't need to reinvent the wheel?

Did we ever survey owners of 91-92 cruisers to see how their gauges perform? I would bet they will swap over directly to a 93-94 at minimum.

I wonder the same question for a foreign 80 or an HDJ81 diesel. You would have to source the other gauge used or from Yazaki because the isnstrument cluster is one part. However MOT could probably ask yazaki.

 

[LandCruiserPhil]

Do you have a picture of where you installed your guage. I'm not familiar with what a "boss" is.

I assume you all are using electrical as opposed to mechanical gauges?

Thanks,
Rookie2

Sending unit installed and gauge mounting

 

[Rookie2]

Thanks Phil. Final stupid question. How does the signal get from the sending unit to the gauge? I would have expected to see a wire coming off the sending unit somewhere.

Thanks,
Rookie2

 

[LandCruiserPhil]

Thanks Phil. Final stupid question. How does the signal get from the sending unit to the gauge? I would have expected to see a wire coming off the sending unit somewhere.

Thanks,
Rookie2

Yes you are correct you should see a wire but the picture was taken durring installation before the wiring

 

[Rookie2]

D'oh. After re-reading my initial request, I guess I was lucky to get that first picture to begin with . "Here's a picture of my installed guage, and a Boss is the guy the just told you to get back to work."

I think I'm in tune now. Just need to get me a gauge.

Thanks,
Rookie2

 

[RavenTai]

hmmm, maybe we don't need to reinvent the wheel?

Did we ever survey owners of 91-92 cruisers to see how their gauges perform? I would bet they will swap over directly to a 93-94 at minimum.

I wonder the same question for a foreign 80 or an HDJ81 diesel. You would have to source the other gauge used or from Yazaki because the isnstrument cluster is one part. However MOT could probably ask yazaki.

I am not aware of any discussion of the FJ-80 temp gage one way or the other. That would be a good thing to find out.

Are the 91-92 and 93-94 dashes the same? I know the dash was changed in 95, don’t know if the cluster was changed at that time, from this Ebay pic the 94 cluster looks externally the same as my 96. Not proof of electrical similarities for the poupose if a mod one way or the other, but still a clue that they may be the same.

This 91 has some slight differences in the AT indicator and slightly different markings on the speedo and tach but from what I can tell the overall layout looks the same and from what I can tell in the small pictures the water temp/oil pressure gage looks identical.

I saw one foreign cluster in a recent thread it was mostly black space and quite different from the American cluster, but I think it was a “poverty pack” truck, have no idea beyond that. Would a RHD cluster be different or the same?

Thanks for the picture ClownMidget.



FWIW, the FSM has the resistance-temparture curve for the temp. sensor. It's logrithmic, with no flat spots.

I recall reading in some previous threads that the temp. gauge was not always like this, but it was changed due to all the soccer moms coming into the dealership thinking their vehicles were overheating because the gauge was read near or at high.

So in my thinking, if Toyota decided to make a change, the logical place to do that would be at the gauge. My guess is that something was added to the circuit board at the gauge, that filters or maintains a similar resistance over a given temperature ranges. But I'm no EE either .


Rookie2

I never had thought to look for that in the FSM but took a look after your post, I found a curve in my 96 FSM for what I think is the ECU sensor in the engine section. It does not match the findings of Rich/Photoman, when you get to the Gauge sensor in the body electrical section it is much more vague.

The one in your FSM is for the gauge?

12. INSPECT ENGINE COOLANT TEMPERATURE RECEIVER
GAUGE OPERATION
(a) Disconnect the connector from the sender gauge.
(b) Turn the ignition switch ON, and check that the receiver
gauge needle indicates COOL.
(c) Ground terminal on the wire harness side connector
through a 3.4 W test bulb.
(d) Turn the ignition switch ON, and check that the bulb lights
up and the receiver gauge needle moves to the hot side.
If operation is as specified, replace the sender gauge. Then recheck
the system. If operation is not as specified, measure the
receiver gauge resistance.

But it does give resistances for the gage, witch are helpful.

The points mentioned below correspond to the schematic above
A= +, pin 5
B= sense out to temp sender, pin 10
C= -, pin 1

13. INSPECT ENGINE COOLANT TEMPERATURE SENDER
GAUGE RESISTANCE
Measure the resistance between terminals.
Between terminals Resistance ()
A – B 71 – 79
A – C 117 – 141
B – C 185 – 215
HINT:
Connect the test leads so that the current from the ohmmeter
can flow according to the above order. This circuit include the
diode.
If resistance value is not as specified, replace the receiver
gauge.

Time to do some math.

 

[Rookie2]

I never had thought to look for that in the FSM but took a look after your post, I found a curve in my 96 FSM for what I think is the ECU sensor in the engine section. It does not match the findings of Rich/Photoman, when you get to the Gauge sensor in the body electrical section it is much more vague.

The one in your FSM is for the gauge?

I don't have my FSM with me right now, but the one I saw I'm pretty sure was for the engine temperature sensor for the factory guage. The graph was for testing the sensor, and had a swoath running through it that showed the range that the resistance should fall in for a given temperature. The scale ranges from 30 kohms down to 0.1 kohms, going from a temperature of 0 to 212 degrees fahrenheit, IIRC.

Do you see this one in you're FSM? It was under the cooling section in the engine division. If you don't have it in yours, I'll scan it and post it.


Rookie2

Edit: It's under the testing for the Engine Coolant Temperature (ECT) Sensor, page EG-166 in the 97 FSM.

 

[slambson]

Raven,

Do you have values for the resistors and inductors drawn?

 

[RavenTai]

Do you see this one in you're FSM? It was under the cooling section in the engine division. If you don't have it in yours, I'll scan it and post it.


Rookie2

Edit: It's under the testing for the Engine Coolant Temperature (ECT) Sensor, page EG-166 in the 97 FSM.

yes I have that one, I think that is the temp sensor for the ECU. nto the temp sensor for the gauge.

 

[RavenTai]

Raven,

Do you have values for the resistors and inductors drawn?

The resistors yes, the resistor in the gauge is marked 75 ohms, The FSM says it can be 71 to 79 ohms (point A to point B) it is the large grey resistor on the right side of the top side pic, the thermistor has been plotted by members here and approximately follows this plot on the miata page. Witch appears to be down right now? i have been using those #'s for now as they are easier to read.

But the inductors not really, after finding resistance of the gauge in the FSM last night I kind of have the resistance of the inductors in pairs,

The needle movement itself is an air core DC motor, these usually have only 2 windings/poles 90 degrees apart forming the stator and a permanent magnet rotor, this one has one large winding and then 2 smaller ones set 90 degrees away forming still only 2 poles but using 3 windings. In the drawing above I drew it as “Y wound” as the three inductors meet in the middle connected to nothing else (the foutth post of the motor that is not connected to anything outside of the motor) . “Y” wound something I had seen in alternators and other AC devices like synchro’s , now I think it would be more accurately drawn as a “T”, I don’t know for sure witch winding is attached to witch points, If I had one to work with I never would need to know this but trying to wok it on paper it is required. For now I am guessing the heavy winding is the one attached to the zener diode.

And I also do not know what the break down voltage (reverse current) of the zener diode is but I think it has a pivotal role in the flat spot and now I am almost certain that it is a zener diode. (Little red centered glass looking bead in the board top side pic).


If you want to work with this one on paper it is easiest to work with drawn out as an “H” shape. Two windings forming the left vertical of the “H” the third winding and zener forming the crossbar, on the right vertical the 75 ohm resistor above the crossbar, the thermistor below the crossbar, connect both sides of the top and mark as source voltage (14.4V) the bottom of the H to ground.

I worked with it some last night and have a potential rough model for how it works. The following #’s are rough and not taken from sources confirmed to be right for the 80 and may be just completely wrong.



It all happens in the crossbar, the left side (center of the 3 windings) has a mostly constant voltage potential, for right now assuming ½ of source (7.2V) the right hand side of the crossbar is connected between the resistor and thermistor, at 100F it is about ~3V at 260F it is ~11V,

When the right side voltage is below left side (cold) current flows left to right forward biasing the Zener diode. As the temperature increases right side voltage increases and left to right current slows, at some point right side will be above left side and stopped by the zener until its break down voltage.

umm gotta go to work

 

[whodat]

This discussion is over my head.

 

[cruiserdan]

From Raven's post:


Quote:
13. INSPECT ENGINE COOLANT TEMPERATURE SENDER
GAUGE RESISTANCE
Measure the resistance between terminals.
Between terminals Resistance (&#61527
A – B 71 – 79
A – C 117 – 141
B – C 185 – 215
HINT:
Connect the test leads so that the current from the ohmmeter
can flow according to the above order. This circuit include the
diode.
If resistance value is not as specified, replace the receiver
gauge.



Interesting. After almost 900 miles towing a boat last week and a CGVW of around 11,000 lbs I saw some interesting stuff on my "dual gauges"

To begin with, I suspect that my 2-year-old OEM fan clutch is shot...

The original gauge hits the "center" at about 140 degrees on my freshly added Isspro and remains there until about 215-218 degrees on the isspro, then it will start to "hike up" a bit. at about 220-223 degrees it reads about 3/4's of the way up. I did not try to push it to get 226 on the Isspro to see if the compressor would cut out. I ran warm pulling the long grades and I did not hear the fan pulling so that is why I suspect the clutch. On the down-hill I would drop as low as 170-175 (I run a 160 thermostat).

My observations are consistant with the OEM gauge being "normal" from about 140 to 215............... One would think a 75 degree swing would merit a but more than that, no?


I was packing a bit of a load tho:

 

[Photoman]

I would just to add some random thoughts to this. While it is very nice to have a gauge that works accurately , I think for some it would be better to have an “idiot” light. The way I did this was with a Greddy temp gauge that has a temperature memory and a warning light that can be set to come on at a temp of my choosing. It’s expensive. It also has an aux. wire that can be connected to an external alarm. I used a large (about ½”) red light and also connected in a piezo buzzer as part of the circuit. This way if the temp gets to my set point the buzzer sounds and the light comes on so I can pull over.
Another way to do this without a gauge, is to use any of the above mentioned ways of tapping into the cooling system and instead of using the temp sensor for an aux. gauge, use something like NAPA part # FS141, which is a coolant fan control switch. It is ¼” NPT threads and comes on at 221-228F and could simply be hooked up to a relay to turn on a warning light and/or a buzzer. There is a multitude of these switches that come on at different temps, so if you don’t like the 221-228F, then pick a different one. Just watch the thread pitch/size and adjust your tap in. This way you can tell the wife, or yourself, if the light comes on, pull over. There are no worries then if the stock needle is this or that close to the H. Oh, if you use a one wire sensor and you connect in the the rad hose, you will have to ground the sensor as a rubber hose does not work well for this. I used the water neck boss for mine and have done a couple for other members so the ground is not required for these. Total parts: sensor, light, relay, wire, guessing $15 US.
I did a little research and found that NAPA sells a replacement temp sensor for the stock (97) one. It is made by Beck Arnley and is part # 201-1678. I could not find the specs for this one, but, the number crosses to a NAPA Echlin TS6036. I found some info on this sensor that says that at 77F it should read 628 ohms, and at 212F 45 ohms. This does not agree with either the FSM (kohms) or the test readings I had gotten a while ago for the sensor in my cruiser.

Repost of chart and gauge with external light. Ramble off.

Bill

 

[RavenTai]

I like the idea of a stand alone temp switch controlling a light and/or buzzer, would make an inexpensive and inconspicuous add on to a linearized stock gage, or cheap easy stand alone for overheat warning.

This does not agree with either the FSM (kohms)

There may be a good reason for this.

The only chart or reference to resistance of a coolant thermistor I have found in the FSM is for the ECT sensor in the Engine SFI section of the FSM page EG-161 for my 96, EG-166 for R2’s 97, It is marked in Kohms, although it does not specifically state so this one is the thermistor for the ECM, not the one for the dash gauge.

In the body electrical section there is some info for the cluster gauge, it calls the thermistor in the block a sender gauge and the cluster needle movement the receiver gauge.

In the EDW the ECM thermistor is called “ENGINE COOLANT TEMP. SENSOR”
The gauge thermistor is called water temp. sender

And most telling is the ECT sensor for the ECU is a two wire, the thermistor pictured with the Kohm chart in the engine section is also a two wire, the gauge thermistor is a single wire (grounds to the block) the thermistor pictured in the body electrical section is a single wire thermistor.



Thanks for reposting the wider thermistor curve. I had been working with the earlier <212F version.

There seams to be a big difference between the two land cruiser charts, any idea why and if possible witch one may be more accurate?

On the 97 LC 80 to 208 F chart, 100F = 450 ohms, 200F = 50 ohms

On the 97 LC 55-275 F chart, 100F = 130 ohms, 200F = 25 ohms, 250F= 10 ohms

On ECT sensor chart, 100F = 1,000 ohms, 200 = 250 ohms

On the Miata chart, 100F = 374 ohms, 200F = 55 ohms, 250F = 26 ohms

The Miata and "80 to 208 F" chart look some what similar, the rest do not line up





On other things, lacking a gauge to work with been playing with the schematic of the gauge circuit. Since first drawing it I have been trying to make it a Wheatstone Bridge circuit , a common and very accurate measuring circuit, but it never had enough resistors as a WB requires 4, we only have 2.

After drawing it as an “H” had an idea, what if two of the inductors in the air core motor play double duty as both stator field and resistor of the bridge circuit. if so the zener diode does not belong, it would be the first thing removed, don’t know how much tuning the gauge would need with resistors after that. Only testing would tell.

First schematic is the “H” described earlier, the second is it rearranged into to shape of a Wheatstone Bridge circuit, all 4 schematics are electrically the same just presented differently, progressing from how it is laid out on the board to an easy to work with common schematic.

L1 though L3 are the three windings of the needle motor, R1 is the 75 ohm resistor. R2 is the thermistor (guage sender) D1 is the Zener diode.

 

[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

 

[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?