Engine overheats when using A/C

[champeny]

My auxillary fan does not turn on as it should. I thought that it was the sender unit (3-prong sensor that plugs into the radiator, see picture) so I replaced it. The auxillary fan still does not turn on and the car overheats when I run the A/C.

I think a related issue is the message I get on my computer each time I start or stop the engine, "Check Coolant Level. See Owner's Manual". The coolant level is fine. I have had this problem since a mechanic changed my radiator a while back.

Another strange thing I noticed is a two-prong connector that does not plug into anything. It is just dangling (see last two pictures).

Anyone know what this is?

[Jared at Pelican Parts]

I had a similar problem with my E30 that I could not figure out. Sensor checked out fine, wiring was fine. Fan never kicked on. I think that BMW must set the sensor to trip on at a ridiculously high temperature. I had the same overheat problem with the A/C on. I simply jumpered the wires going to the sensor, fan now kicks on high speed whenever I turn the A/C on. This also helped my A/C blow a bit colder as well..

You might want to try turning the A/C on, and then unplug the connector (the black three prong connector in the top picture of the post here) and jumper the connections to find out what the low and high speed is. (I eventually rigged it to a switch that I can control manually) If the fan does not kick on then, you have a wiring fault somewhere.

[champeny]

When you say you "jumpered" the wires, how exactly did you do this?
Thanks

[Jared at Pelican Parts]

I crimped jumper connections between the wires. In your case, just take some wire, and touch the contacts inside the connector prior to hard wiring it.

[Eli at Pelican Parts]

Those connectors look like the same one I have on my fog-lamps. Could be wrong, it's been a while since I've been down below....

I would rule out the aux fan myself and look towards the cooling system like the water pump and the thermostat. One last thing, if your radiator cap is not sealing that could also be the cause of malfunction, trust me when people don’t believe me I ask them to try it, amazingly I’ve had a few become believers…..

Good Luck!

-Eli

[champeny]

Eli,
Interesting...A while back my radiator blew at the top hose fitting. My water pump went out at the same time - due to the fact that I was on the freeway and had to drive to the next exit. Conveniently (but not for me) I broke down a block away from a German car shop who replaced my radiator, water pump, and thermostat. So those things are newly replaced, apparently.

I'm thinking the thermostat may be the easiest and cheapest to check out.

But I'm not sure that I understand the relational correspondence to the auxillary fan not engaging as I thought this was an electrical function. I'm sure it is my lack of knowledge.

[Eli at Pelican Parts]

Originally posted by champeny
Eli,
Interesting...A while back my radiator blew at the top hose fitting. My water pump went out at the same time - due to the fact that I was on the freeway and had to drive to the next exit. Conveniently (but not for me) I broke down a block away from a German car shop who replaced my radiator, water pump, and thermostat. So those things are newly replaced, apparently.

I'm thinking the thermostat may be the easiest and cheapest to check out.

But I'm not sure that I understand the relational correspondence to the auxillary fan not engaging as I thought this was an electrical function. I'm sure it is my lack of knowledge.

Nothing should really happen if your auxillary fan is pulled of the car but it does help when you're in traffic or on those extremely hot days when the A/C is on. . .

BTW: Is your fan clutch working properly?

-Eli

[champeny]

I am not sure about the fan clutch. I did check this previously. I think the symptom to check was that the fan would be running very weak and you could stop the running fan with your hand if the clutch was bad.

This was not the case for my fan - it seems to be running at proper speed. Am I off here?

Any tech articles on checking this out / replacing?
Thanks,

[Jared at Pelican Parts]

DO NOT stick your hand into a spinning cooling fan....

Use a piece of newspaper...

[champeny]

Yes, good point.

[Jared at Pelican Parts]

Eli is correct, a faulty cap can cause the car to overheat. A faulty fan clutch will almost certianly cause overheating.

[champeny]

I replaced the cap, so I don't think that is the problem.
Fan clutches are not cheap, so I prefer not to do this unless I am certain that this is the problem.

Is there a certain method of diagnosing that anyone knows about?

[Eli at Pelican Parts]

How to test the fan clutch:

Sorry guys, the newspaper test is not reliable. If the thermostat doesn't work or is slow moving, the fan clutch will fail the newspaper test and will spin freely don't even bother explaining how it is done as it is dangerous.

What you should do:

1) make sure that the thermostat is working!
2) when the car is cold, the fan clutch should turn with a small resistance and not spin freely.
3) Let the car idling and the hood not closed but down. After 5-10 min, the temperature will rise at the 1/2 mark, check that the fan is blowing a LOT of air inside the engine compartment and increase in noise level, no need to put your hands, you will feel it. If when the temperature hits the 3/4 mark, the fan is not blowing a lot of air, that means that: either the thermostat is not working or slow, or the fan clutch is bad.

Hope this bit of information helps,

-Eli

[BMWCowboy]

That white plug is the alarm plug>>but you should have a 2-prong black plug plugged in at the bottom of ur expansion tank>>if ur car overheated it may have burned-up...thats ur level sensor>>>have U checkd the aux fan fuse???.....if its good then U need a new aux fan resistor>>>its right on the fan & has to be soldered on~