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Cooling fans come on late - why?

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I had an expansion tank cap fail on me today, causing a leak - total amount lost was maybe 125 ml. I procured a new one, installed it and drove around. No apparent leaks.

However, during the cruising around I used the climate control hack which showed 94C to 97C in traffic (as high as 100 stopped at a light) and 92 to 94 in clean air (ambient temperature 75F) and no evidence of the fans coming on at any speed.

I checked when I got home and discovered that the low speed fans do not switch on until the climate control hack show 103C and my Durametric shows 100.5C (it appears that the climate control is 2.5C to 3C high across the range).

This fan behaviour seems a bit strange as they are supposed to come on at 96.75C for the low speed.

Any ideas?

Many thanks

Edited by fbgh2o
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No, I did not. However, I would not have thought that a leak at the cap would require bleeding the system. The amount lost was maybe 125 to 250 ml - It was still above the min line on the tank.

Moreover, I am 99% sure that the fan operated this way before as well.

Edited by fbgh2o
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Does anyone know where the climate control gets that temperature from - I don't think so.

I don't think the turn on temp is critical as long as the car is not overheating. I live in Northern California and it has been over 100 degrees F the last 4 days in a row. My temp needle still rarely goes much past the 8 in 180.

My fans seem to only "need" to turn on when stopped at a light or other idling time (other than AC of course). I own a PST2, PIWIS and Durametric and I have not bothered to look at the temperature readout - because the the car does not seem to be overheating or have a problem.

Personally I think too many folks have blown the cooling thing way out proportion - heat is not killing these cars.

My advice is - if your car is not getting hot - don't worry about it.

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