I got a question about the coolant temp sensor. I just replaced the coolant temp sensor on my nephews 94' 3.0 V6 4runner for him because he said that was what he was told was giving him such bad gas mileage.

When I pulled it out the sensor it was completely dry and no coolant came out of the opening at all.

This being my old truck I remembered that the dealer did the last head gasket repair. I also remember hearing that they use a lot of FIPG (form in place gasket) and sure enough when I got back there and cleaned out the openings coolant came flowing out with black FIPG.

I did the same for the sensor that reads the cold start injector and it was clogged too. After doing this it's already getting way better gas mileage.

What I want to know is, would this change what the coolant temp sensor and the cold start injector read and sent to the computer. He said it never threw a check engine light, so I am just guessing that this is what it was.

I want to hear from someone who may have more knowledge on this because my neighbor has the same engine and the same crappy gas mileage on his 4Runner.

RRIND

 

Any time a coolant sensor is not in coolant it will not send a valid signal.

think of just having the sensor laying on the housing instead of threaded in about the same thing.

Had a boss run a engine low on coolant (the type to never check things) because the temperature gauge always read close to normal he just kept going to the engine seized.

He said " the temperature was normal"

 

The ECU didn't throw a code because the sensor reading was valid ("engine is cool"), it just wasn't correct. So the truck was running is "cold" mode, meaning it was running much richer than it should, and it was mostly ignoring the O2 sensor.

The "stuff" might not have been FIPG. While I've never seen it myself, I've heard of several instances like yours, where a sensor was coated with enough "stuff" that when removed it left behind enough of a membrane that the coolant didn't come through.

But there's no reason to think that the stuff, FIPG or otherwise, was limited to sensor openings. I would consider a real coolant flush. If enough of that stuff gets together to block a coolant passage, you could have a real problem.

 

Is there a way to check and see if the coolant temp sensor works properly? I searched a bit but I wasn't able to find anything specific..


I have 1994 22re that is having warm start issues and smells like it runs rich so I would like to check it if possible before I spend any money.


Thanks!

 

Here is the curve of resistance and output voltage vs. temperature for the ECT. You can use a multi-meter to see if it's giving you reasonable output. For more accuracy, pull it out, stick it in a pan of water with a cooking thermometer, and watch the resistance as you heat it up. (Basically, it's a 2.2Kohm thermistor - reads 2.2K at 25degC. They're used everywhere in the electronics industry)