735I Overheating

[bandja]

I'll get right to it......'92 735I, 120,000 mi. Have had issues over the last six weeks or so with overheating. Car temp is normal, then suddenly skyrockets and sometimes comes back to normal. Other times there is nothing you can do but pull over and let it cool down. I have found no visible leaks, thermostat is six months old, no water (coolant) in the oil, no unusual odor or discharge from the exhaust. It makes no difference what the outside air temperature is. It may go 2 weeks between incidents and it may go 2 hours.

I love this car and would like to drive it for years to come but stranded along side the road is not an option.

I am out of ideas so have come to the experts.

Thanks in Advance, Bandja in KC

[y2khris]

Make sure that the fan clutch is good. I have seen those things go bad more than once.

[bandja]

Forgot to add.....Fan Clutch is new????

Thanks, Bill

[mjeet]

having same problems with a 2000 740il. Temperature shows normal on startup then after a second it suddenly jumps to hot. Car has been in standing in garage for about 3 hours and added more coolant but it still jumps to hot. Could the temperture sensor have messed up ??

[jyep]

I was gonna say the same thing, you sure it's just not a faulty temp sensor; they do go bad ocasionally.

[TECH]

Just a note to those who have the dual temp sensors on the thermostat housing.....

The two connectors will interchange between the two sensors, so it's possible to get them crossed. If that happens, the temp gauge will go full hot after the car warms up. The sensors are NOT the same.......

It's bitten people before.

To the original poster, thermstats can go bad whenever they feel ready........
Check to see that the auxillary fan works.

[NVMYM5]

I need help...Have the same over heateing problem. In fact overheated on me 3 times in past 2 months. Changed the fan clutch the first time, then changed the radiator. After each replacement, it was good for a week. Then, she was back to the red. Is there a possible cracked cylinder head or another engine problem.

[slyhog-22056]

Dont forget to turn on the heat and bleed the excess air out of the thermostat housing by speeding the engine up and then bleed at idle several times. Mine drove me nuts for a couple of days after changing coolant when I bought it used.

[1983_633_CSi]

My 1983 633 has been running hot for about 5 months. I had one guy tell me it was the fan clutch. I later took it to a local dealer and they said it was a faulty sensor. There are three sensors on the top of my engine. Has anyone resolved this apparent overheating problem? I say "apparent" because during the diagnostic, the engine never went above 190 degrees even when in the "RED."

[Silver4evr]

Bandja: Sensors, connections, wiring, temp. gauge., everything else in the cooling system that you haven't changed. Have a diagnostic run like 1983_633_csi.

Same for all the other posters.

[markca]

My overheating problems occurred after I changed out a cracked radiator on a 91' 735i . Thought I blead the system but still had an air pocket in the system plus had a bad clutch fan. Had clutch fan replaced and system bled by a BMW mechanic. Two weeks later started over heating again. Read forum and found out to bleed in front and behind thermostat. Still carry wrenches and coolant just in case but car has been running fine for past week. Still don't know if problem is fixed.
No visiable leaks but the hoses still get a large amount of pressure on them. Is this normal?

[Torque]

to test fan clutch: when the engine is shut off and key removed, spin the fan. it should spin with some resistance... if it spins freely it's gone south.

try getting a new thermostat that opens at lower temp (bavauto.com has it). if both of the things listed above are ok, then you either have air in your cooling system or you have a bad water pump.

www.bmwe34.net has some good info on this (i know you have a e32, but the cooling system is the same). info can be found under their troubleshooting>overheating, but i don't think it will tell you anything i didn't.

good luck

[Torque]

i hope you don't let the temp go all the way into the red area... it only takes a few times and you'll be in the market for a new head/head gasket.