Temperature gauge & sensors / senders / switches - Toyota Nation Forum : Toyota Car and Truck Forums
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#1 Old 07-08-2012, 08:21 PM
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Question Temperature gauge & sensors / senders / switches

I've browsed a lot of other threads on this stuff but I'm still a little lost.

I've got a '95 2.2L/LE sedan/auto and the temperature gauge pins as soon as the key is in on position (even with engine completely cool).

For some reason, on extended trips it starts to slowly go down until it settles to display a normal running temp.

Rock Auto puts the temperature sensor and temperature sender under the same section... don't these serve two distinct purposes? Correct me if I'm wrong: one of them sends coolant temp info to the gauge, and the other serves to switch the radiator fans on/off. Which one should I be looking at for my gauge issue?

And what is its location? I read that it should be near the thermostat, but I don't see anything that looks like this piece over there. Is it one of the pieces in the picture below (on or near the water exit block)?

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#2 Old 07-08-2012, 09:31 PM
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The gauge "sender" is the one-wire one. The sensor for the ECU is the two-wire one.
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#3 Old 07-08-2012, 10:00 PM
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There are actually three coolant temperature sensors.

1) The ECT which feeds the ECU. That one's in your picture; the one on the left with the green connector on it.

2) The fan sensor, or more accurately, switch. On the 4 cylinder, it's mounted in the radiator at the bottom on the passenger side.

3) The sensor the gauge uses. Not sure where it is on the 4 cyl, but I *think* it's in your pic, the one next to the green one.

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#4 Old 07-08-2012, 10:07 PM
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If this is an image of your engine, then the aluminum appears corroded. I would guess this is from traveling on salted winter roads? Is it possible that the temperature sender / connection fitting is loaded up with corrosion salts, is damp with moisture and then grounds / shorts the temperature sender / connection fitting interface?


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#5 Old 07-09-2012, 10:35 AM
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Thanks for your help everyone.

Yes, it could most definitely be a corrosion issue, I live in the northeast. I popped one of these connectors off (without knowing whether it was the right one) just to see how the contact components looked. They didn't appear as bad as the exposed components seen in the photo, but I'm not ruling it out.

I will probably just replace it since it is a relatively cheap part. I'm hoping it is not the gauge itself, but the fact that it settles down on long trips makes me think it might be on the sensor side.

The car had some traumatic cooling system issues in the past that may have affected this and other components .
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#6 Old 07-09-2012, 08:50 PM
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The sensor would be the cheapest and easiest thing to replace (it's just a thermal resistor). But, if it's reading high at the sensor, your rad fan should be constantly running. If that isn't happening, I'd start looking somewhere else, other than the sensor.
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#7 Old 07-12-2012, 11:29 PM
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Follow up: Luckily this was the correct sensor I got off a 5sfe at the junkyard even though I wasn't sure. I removed my defective one (17mm deep socket) and immediately saw the problem. The 'thermowell' part of the sensor was deformed with a nice hole in one side:



This must have been a result of the traumatic cooling system issues I previously mentioned. Let's just say things got pretty hot on a couple of occasions. Fixed leaks, new thermostat, radiator cap etc. but I guess this was some collateral damage. I should probably replace the other sensor for the ECU as well.

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Originally Posted by CrystalMethod View Post
The sensor would be the cheapest and easiest thing to replace (it's just a thermal resistor). But, if it's reading high at the sensor, your rad fan should be constantly running. If that isn't happening, I'd start looking somewhere else, other than the sensor.
As previously mentioned, the fans are controlled by a temp. sensing switch on the radiator. As a precaution while my gauge wasn't working, I had the switch unplugged so the fans would always run. I plugged it back in after the repair and let the car idle for a while, but it never got hot enough to see if the fans would turn on automatically.

Last edited by DogToggler; 07-12-2012 at 11:30 PM.
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