Hello again folks,

Just got the car put back together after doing the PCV system and, while running her for the first time, I noticed that the cooling fan doesn't ever kick on. The car threw a coolant temperature sensor code before so I replaced the sensor while I had the intake manifold off. Also, I have confirmed that the fan itself works by disconnecting the coolant temperature sensor and turning the key to the on position (fan runs continuously then, presumably because there is infinite resistance between the two wires of the sensor plug).


Now, for my questions:

1. Since the cooling fan works and the coolant temp. sensor is brand new, the fault is most likely in the relay, right? If the relay was bad, though, would the fan kick on when the coolant temp sensor was disconnected? It seems like that would be a response to the infinite resistance between the sensor pins, which indicates that the fan turning on is a result of the ECU activating the fan.

2. If not the relay, what else could cause the fan not to run?

3. How hot is the car supposed to get just idling with the fan off? I ask because I had it sitting for about 10 minutes, and the temperature gauge never went above the halfway mark. Since the temp sensor is new, could there be another fault causing the gauge not to display the proper temperature?

 

Sounds to me like your thermostat may be stuck open. If your temp gauge seems to work now and it stays below 3 o'clock position after 5-10 minutes of driving, then replace the therm.

 

Sorry, forgot to mention, thermostat was replaced at the same time as the coolant temp sensor with one from the dealership. Is there a chance it's defective?

 

I'm for thinking it's the thermostat that's bad. Without the fan working the gauge should keep climbing until it boils out the reservoir tank.

 

OK, I should be able to pull the 'stat and put it in a pot of boiling water to test if it works, correct?

 

Yeah sure, but I'm waiting for the answer to my question in post #2; what does you gauge do?

 

You should be able to pull it out and just inspect it to see if it's already open. You're problem, if it's the thermostat is that it's open too soon !!

It should be closed when you take it out and if you put it in 150/160 degree warm water it should still be CLOSED. That's how it would allow the engine to reach operating temperature.

If you stick it in boiling water and it didn't open it would show that it's bad and causing the overheating problem, a problem you don't have

 

I'm sorry I missed that one. The gauge goes up to 3 o'clock and stays at exactly 3 o'clock. Doesn't climb at all past there, even though the fan never kicks on.

 

No need to boil the thermostat then.

You are troubleshooting perfection.

 

I doubt you have a problem at all, the fan should only come on if the temp reaches 216° F. My fan rarely comes on while sitting in the driveway unless I have the AC on. Driving around with a load, more fuel, etc. raises the motor temp, the motor may never get over 200° while sitting idle. Unless you check the temp with an OBD2 scanner or have an IR temp reader pointed to a radiator hose, I would not tear into unless you see the needle above the 3 o'clock position.

 

OK, thank you for the advice fellas. It just seemed odd to me that the temperature wouldn't rise without airflow over the radiator. I used to have a car that would raise 10 degrees at red lights, I guess the cooling system in my 850 is just more efficient.

 

That and the fuel injection.
I had a Geo Metro 3 cylinder and that sucker in winter wouldn't produce enough heat to defrost the windows no matter how long you idled it. I liked to go out and start my cars up and let them melt the snow and ice rather than scrape. Not on the Metro !! Until you started driving it there wasn't enough fuel burned to get the coolant hot enough to clear the windows.

 

My fan cycles on an off at idle, however the weather here is quite warm. You could always simulate a hot day by putting a heater in front of the car to see if that trips the extra cooling of the fan. It's what I have done in winter when trying to troubleshoot cooling issues.

 

Methinks the ambient temperature here in Wisconsin had everything to do with it. The fan kicked on today for the first time, when the car had been running while parked for 20 minutes straight while I was flushing the cooling system. Glad to know for sure it works!