Engine overheating

AJMACKEY

MEMBER
2008 BMW 328XI
6 CYL
4WD
AUTOMATIC
119,000 MILES

There is plenty of coolant with no leaks. I bled the system so the water pump is working but my fan only seems to come on when the AC is working. So the fan is working, but is there some sensor somewhere that tells the fan to come on when the engine gets hot? If so, where and what is it? Or can it be something else? Can the thermostat have something to do with this? Any suggestions?

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,758 POSTS

HI and thanks for using 2CarPros.com.

It could be a few things. First, can you let me know if it overheats at highway speeds or only when you are driving slow such as in stop and go traffic?

If it overheats at highway speeds, it could be a bad thermostat. However, if it is only at low speeds, then the fan is most likely the cause.

Here is a quick check on the fan, Take a look through this link. It discusses the two types of cooling fans.

https://www.2carpros.com/articles/how-an-electric-cooling-fan-works

Also, here are a couple things you could check if you feel it is a fan issue. Check fuses F92 and F28. See attached picture 1. Also, in the same location is the electric fan cut-out relay. If there is another relay with the same part number, switch them to see if it makes a difference. Or, here are the directions for checking a relay.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Also, check the radiator output temperature sensor's connection for corrosion. Picture 2 and 3 shows its location. Also, check the temp sensor on the right side/front of the cylinder head. Make sure wiring is in good condition with no corrosion. Picture 4 shows its location.

Let me know if vehicle speed has affect on the overheating. That will help me determine what could be the problem.

I hope this helps.

Take care,
Joe

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