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Discussion Starter · #1 ·
The radiator fan turns on at cold startup. It is not constant on, it runs at high speed (full blast) for about 3 seconds and then off. This cycles on and off for about a few minutes. The length of time cycling on and off seems to correlate to the temperature. It is longer at colder temperature (outside/engine). This issue doesn't happen if engine is warm.

I've seen threads, where people attribute this to many things, such as temp sensor, fan, water pump.

I've replaced the sensor already without a fix. And I don't want to chase parts to fix issue.

I would like to know if there is any easy way to determine the root cause?

The coolant level is proper. Temp sensor is new. The fan turns on when engine temperature reaches warm/hot (can't remember the exact temp when fan kicked on).


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Mine occasionally does the same thing. My car came to me with a new water pump, and I'm not getting any idrive or cel or codes, so I figured this may be a normal thing on these cars?

Hopefully someone with more experience/ knowledge will chime in.

Like you, my coolant level is good also.
 

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The ECT needs to be viewed on a scan tool as well as some other DME parameters when engine is started cold. Otherwise it will remain a raise hood throw on some parts repair attempt.
It might be worth the effort to remove ECT sensor connector and carefully close down the "fingers" of the connectors and then apply some dielectric grease (spray white lithium grease will do) and re-connect. Resistive connection can make DME go into FMEM (default mode) momentarily and fan on is one of the actions.
Short to ground, even resistive contact that is not a full short, can either make DEM think engine is hot or cause FMEM.

When runs on start is there any coarseness in the way engine runs?
 

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Just an idea, but could this be normal? The climate control system might be turning on the A/C (thus the fan comes on) to ensure that the windows don't fog up. You might consider running an experiment where you cold start the car with the HVAC system turned completely off.

Keith
 

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Discussion Starter · #5 ·
I'll check and clean connections. That would make sense.
What code reader should I buy. I've been lucky enough to get by with generic scanner all these years. The generic reader doesn't see any issues.


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Discussion Starter · #8 ·
No solution yet. So far I've changed the sensor and cleaned connections without resolution.

If I turn off the climate control on startup, the fan doesn't go crazy at startup. So it seems like something is goofed up with the electronics.

Maybe related to the same issue... I always have the climate control on automatic. Sometimes when I'm driving, the cabin fan kicks on high speed and blows either hot air or nonAC air for maybe 5 to 10 seconds. Then it all returns to normal.
Could all this be related? Could it be just the FSR?


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