I replaced the coolant sensor in the side of the driver's head that's used for the dash gauge. I didn't drain the block, but not a lot of coolant came running out. The problem I have now is that the dash always reads at the last white mark before the red (shows the car heating up, its not stuck), this is while driving down the highway and while parked.

What is weird about this overheating problem is that if I remove the thermostat the problem goes away, and will hover between the middle and quarter white lines. I replaced the thermostat with a new one, and also verified that it opens and closes properly. I bled all the air that I can out of the system, only streams of coolant come out of the bleeder valves. I left the radiator cap off and revved the car and could see that the pump is pumping coolant like it should (the pump is about a year old).

I read the car's computer and the PCM (seeing the temp sensor in the water pump) says the car is about 210*F (the middle white mark). Yet the one in the head is seeing 250*F or whatever is just before the 260 mark.

If anyone has had a similar problem and/or a fix please let me know.

 

Did you install a GM sensor? Many auto stores sell the wrong one or they just don't work right.

 

No I did not, the one I got is here http://www.oreillyauto.com/site/c/de...r%21s%21sender. Would it make that much of a difference? I have boughten quite a few things from generic auto parts stores and they have worked fine.

 

I would trust the oem sensor in the WP before the aftermarket one in the head. I would grab a GM sensor and see how things look before spending much more time with it.

 

Is that a single-pin sensor or a 2-pin?

 

I got a new sensor, and checked the resistance against the now 2 new ones, and the original one. All 3 were within 20 ohms of each other after laying in the sun, being roughly 1400 ohms for each.

This is a one wire sensor. The middle pin is not used. It uses the chassis ground instead.

I am racking my brain on this one. I have drained the coolant from the radiator a couple times, although not from the block, and each refill results in the same. The only things I can think of now is I knocked some sediment loose and clogged the radiator so it's blocking flow after replacing the sensor, it's not getting a good ground with the block so the resistance is off (there was some red lock tight type stuff on the threads), or something else.

 

did you bleed the air out of the system, last year when some guys tore my water pump out they had to remove the radiator, when they did they didn't bleed the air and it was running hot... once the air was bled out the car was fine!

 

I replaced the sensor with a genuine GM one from my '93 S10 (same part number, 3 dealers confirmed this) and now the car runs in the normal range (around white mark between 160* and half white mark).

For anyone in the future that is having the same problem, the one from O'Reilly will not work. They have too steep of a resistance curve and will read hot at operating temperatures.