Need Help Diagnosing Oveheating - BMW Forum

dougdow · 03-06-2005, 03:47 PM

i finally own a BMW! and have a feeling i'll be using this forum a lot. the temperature gauge on my '94 325i occasionally has red-lined rapidly, then would usually go back down to the middle mark just as quick when I decelerated or stopped. bled the air out of the system but still had the problem. last time the gauge red-lined it took a while for the engine to cool down. no coolant smell, no coolant in the oil, no peculiar exhaust color, no discernible loss of coolant. realizing this is a common topic (i've been all over this forum and the web, which has helped tremendously with what I've done so far) I still have some questions. i removed the thermostat which was the wrong one, 92 instead of 190 degrees, which leads me to suspect it was installed in an attempt to compensate for another problem (and may be a cause for the rough idling when cold) but it operated fine in a pot of boiling water. i removed the water pump which is I'm guessing the original, the impellers are plastic and a sickly orange color, but the impeller is completely intact and the bearing seems fine. noticed some corrosion in the thermostat and waterpump housing. should i try an additive coolant flush to eliminate the corrosion? can i test the fan off the car (waiting on parts before I can reassemble)? any suggestions for my next step would be greatly appreciated. thanks

AdoreGSX · 03-06-2005, 05:50 PM

The stock impellers go bad. Replacing the waterpump would be my next move. I had to do it on mine as well.

Ice90 · 03-06-2005, 10:34 PM

That used to happen to me to, when i woudl sit at idle for a long time the temp needle would begin to rise try this,, if it rises up while ur stopped in nuteral rev the engine to about 3000 revs and keep it there if the temp goes down you need to get ur coolent system flushed and cleaned it should be good after thaat....

97alpineM3 · 03-07-2005, 03:24 AM

I dont have a manual with me... cause I'm in Iraq... but BMWs dont use a 190deg thermostate.. I have a 72 deg one in my car... its a little lower thermo to allow it to cool down a little sooner... from, I think 87 deg. I would do a little checking into this if I was you.. because 190 is by far not the right thermo...

I wish I could help more.. but no manual where I'm at...

Good Luck,

Les

walshja · 03-07-2005, 02:39 PM

I just recently experienced the same problems as yourself.

My heater core was the cuplrit, as that is where I was losing coolant, but this does not sound like your problem.

The problem with your temperature rising and falling has to be 1 of 2 things, a bad thermostat, or an improperly bled cooling system. Is your overfill tank filled with coolant? If not keep adding coolant after the car cools down until it remains full even after the car cools down, I understand this is how you bleed the cooling system.

Your waterpump sounds OK, if the propellars are in tact, but maybe it is not spinning adequately.

I would focus on ensuring your system is bled properly, as I think that may be the culprit. Remember to run your heater on full blast to fill the heater core with coolant.

let me know what you find out.

good luck

dougdow · 03-22-2005, 05:09 PM

Finally got my parts and found the time to reassemble my ride. New waterpump, thermostat, thermostat housing, hoses and flushed the radiator and block. Been driving the car and haven't had any temperature spikes but... the heat goes from lukewarm at idle to very hot when the car is revved up. One day I got the car to operating temp. and got no heat so I bled the system for about the fourth time in 3 days. Pretty sure I'm bleeding the system right so it seems to me I have a leak somewhere, I imagine a pressure test will tell me if there is a leak but not what is leaking. Again, none of the common signs of head gasket or heater core though I am beginning to suspect one of these. Anybody have any ideas on diagnosing this problem before I just start spending a bunch of time and money guessing at repairs? Incidentally, while looking around the web I found what looks like fairly comphrehensive directions for replacing a heater core at- www.babcox.com/editorial/ic/ic80136.htm .
Thanks for the help.

frank3 · 03-22-2005, 05:57 PM

Car shouldn't go to "very hot"...mine never rises above half-way. Given what you've done, it sounds like there may be problems with the radiator (even though you flushed the system). May want to take it to a mechanic to get his opinion...then, you could always fix it yourself.

3serbmdubya · 03-23-2005, 01:50 AM

oh snap sounds to me you got a blown head gasket. all these symptoms lead right to it. the temp gauge spike thing is because since you got a leak on your head gasket i read that gas fumes leak into coolant system and when you accel/decel the fumes go in and evaporate and messes up the gauge.

a good way to check this is to check your oil and see if its milky white or there is white residue on dipstick, constant white smoke from your exhaust and a leak test.