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I have a suspicion that my cooling fans may not be working. In order to be sure, I was wondering when are the fans supposed to come on. Its been really cold here and I haven't driven much in the past few months to heat up the car enough to make the fans come on. I recently replaced the rad and did the bleeding procedure and I noticed that the fans didn't come on once the car had reached normal operating temperature. I have a new engine, new rad and just changed back to a new OEM thermostat. I know both fans work because when I turn the ignition, I can hear them running and then they turn off once the car is started.

If the fans are not working I am guessing that either the rad fan sensor (at the bottom of the radiator) has a loose connection or I didnt connect the FCU properly when I swapped the ECU. Can someone tell me what exactly tells the fans to come on once there is a need for them to come on?

Also, on a cold start, the initial RPMs are 2000 and then gradually come down to ~1000 (takes about a couple of minutes in sub-zero temperatures). However, sometimes if I shift into drive while the RPMs are at 1500 and then put it back into park, the RPMs start to fluctuate between 1500 & 2000 (couple of times) before settling at ~1000. I know for a fact there is no air in my system. I just compression tested the engine; its fine. Are these signs of a dying Coolant Temp Sensor?

I need to figure this out before it starts getting warm here.
 

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I have a suspicion that my cooling fans may not be working. In order to be sure, I was wondering when are the fans supposed to come on. Its been really cold here and I haven't driven much in the past few months to heat up the car enough to make the fans come on. I recently replaced the rad and did the bleeding procedure and I noticed that the fans didn't come on once the car had reached normal operating temperature. I have a new engine, new rad and just changed back to a new OEM thermostat. I know both fans work because when I turn the ignition, I can hear them running and then they turn off once the car is started.

If the fans are not working I am guessing that either the rad fan sensor (at the bottom of the radiator) has a loose connection or I didnt connect the FCU properly when I swapped the ECU. Can someone tell me what exactly tells the fans to come on once there is a need for them to come on?

Also, on a cold start, the initial RPMs are 2000 and then gradually come down to ~1000 (takes about a couple of minutes in sub-zero temperatures). However, sometimes if I shift into drive while the RPMs are at 1500 and then put it back into park, the RPMs start to fluctuate between 1500 & 2000 (couple of times) before settling at ~1000. I know for a fact there is no air in my system. I just compression tested the engine; its fine. Are these signs of a dying Coolant Temp Sensor?

I need to figure this out before it starts getting warm here.
There are a few things that can lead to the fans not running IIRC: coolant temp sensor being one of them.

The fans don't come on as soon as the car reaches operating temperature. Having just done the bleed process myself, I was shocked at how long after the needle is at normal operating temp. but I was still cooling my heels watching the fans wondering WTF was up.

At idle, it's probably another 5 minutes or so before the fans will start cycling... when it's super cold (as I imagine it is up there) I wouldn't be surprised if it takes a great deal longer still (or hell... it might be cold enough that they actually do not need to turn on: the ambient temperature of the air around the radiator might be enough to keep the temps down w/o the fans on).
 

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Tony you should turn your car on and then turn on your A/C and check to see if both fans are working when your A/C is on. They should both be working at that point. If they don't work or only one is working I would then go to the bottom of the car to where the fans connect to the lower sensor on the Rad. Unplug the fans from the sensor and jump it with a paperclip (same way you jump the ECU to get a CEL code). when you do that the fans should immediately turn on (both). If they don't both kick on I would do a relay swap to see if they work. this will probably solve your issue. If not I would check the FCU and the Fan Timer module.

The only thing I've experienced with a bad coolent temp sensor is that you will get a false reading on your temp gauge (overheating)


I'm overlooking the sensor on the bottom of the Rad since you said it was a new rad, so I'm assuming new bottom sensor.
 
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