1991 750 il running hot sometimes??

ohio_porsche · 09-04-2009, 01:31 PM

My 750il overall is in good shape, but lately I notice the temp gauge climbing up to the 3/4 range, and at most sometimes just a little away from the edge of red. It doesnt always do this and it doesnt always correlate with how hot it is outside. I wonder if it can be an intermittent electrical dysfunction of sorts. When I start the car the fan is running but I wonder if maybe it turns off while driving??? I'm really not sure

Had the cooling system drained and refilled and got an oil change (needed anyways) and it is still doing this even when driving on the highway. Transmission and differential fluids are fine.

Any advice or links on how to approach diagnosis? I wanted to put in a cooler fan switch anyhow (one that turns on the fan sooner) since it is summertime here and I'm probably moving to a hotter state soon anyways.
I dont mind replacing the thermostat, temp sensor /switches etc so long as it is pretty easy do it yourself stuff, since obviously cooling is an important part of preventive maintenance. There are no cooling leaks and coolant is at proper level and fresh

thanks!

ohio_porsche · 09-05-2009, 07:17 PM

i think there was air vs small clog in the system, bled the system but also installed a cooler (80/88 i think) cooling fan switch after flushing system and coolant overflow tank too (had some gunk)
now its all working fine, even with AC on and idling, stays at halfway like it should =)

shogun · 09-06-2009, 02:51 PM

clean this hole so that coolant is always returning from the tank, this is the top of the coolant expansion tank
http://www.nmia.com/~dgnrg/ret2.jpg
if that one is clogged, even sometimes, it can overheat and it also does not bleed automatically the complete system.
Once the engine warms up enough to open the thermostat, small stream of coolant should flow near the fill cap letting you know the bleeding has been successful

There is no need to change for another system, the 750 system is enough if all works. Here in Japan we have in summer 40 degrees Celsius and my car does not overheat. And my car is chipped (own chips)

Check the fan clutch
http://www.bimmerboard.com/forums/posts/455673/

check the belt tensioning of the fan clutch.

hot climate improvement
http://www.bimmerboard.com/forums/posts/337575/

there are evn pulleys for the visco fan for hot climate countries, so that the visco is always running at higher speed. That is installed in my car as standard. See ETK for the parts, you need a new pulley and a new belt.

The aux fan should usually run in step 1 only, step 2 is for emergency only.
http://www.bmw4life.com/auxFanR.htm

If it is only sometimes, I first would check the belt tensin, change the belt tensioner, check the flow in the return line, and the visco clutch.

Aux fan is basically not needed, except in stop and go.
And check the thermostat again, even if it has been changed recently, they can break quick, have seen some broken ones this sommer which were stuck then.