735il Cooling Problem

A few months ago I purchased a 1990 735il and have had cooling problems with it ever since. It started with intermittent leaking at the seam where the lower radiator hose meets the thermostat housing. Eventually, the lower radiator hose blew out. I replaced it, but as soon as I started the car it immediately overheated. My next step was to change the thermostat. (Note: When I removed the old thermostat it was obvious that the person who had installed it had snipped off the inner portion of the thermostat. I don't know why someone would do this, but I figured it must have some significance). When that was done I thought I had solved the problem. The car drove perfectly on a 50 mile drive after replacing the thermostat. A few days later I was sitting at idle and the car began overheating again. I shut it down, let it cool off and drove home without issue. It now seems to run fine and the temp gauge stays at 12:00 as long as I keep driving, but when at idle it seems to overheat.

It should also be noted that there seems to be some oil getting into the coolant system. I am making plans to replace the head gasket at this point, but only seems to be a one way problem as there is no evidence that coolant is getting into the oil. While every response is appreciated, I am not much of a car guy, so if you could keep your advice in layman’s terms that would be great.

Thanks.

If it is tranfering oil into the coolant there is a bad headgasket.

Since it is an aluminum head on a steel block it can do very small leaks at certain temperatures initially.

It always gets worse.

You may want to get the valves looked at with the head off?

Later,

Normal temperature while driving but overheating at stops is usually a symptom that a fan is not working properly to draw air through the radiator. My '93 740iL has two fans. One in front of the radiator and one behind it.

Not sure about the rear one, but the one in front is supposed to run always when the A/C is on and is switched on via coolant temperature at other times. It also has a high-speed and a low-speed.

Try this: Start the car, turn on the A/C, then walk around to the front of the car and peak in there to see if the fan is running. If not, it might be just a fuse. Otherwise it's a relay, the sensor/switch on top of the radiator, or the fan itself. Fan from the dealer is ~$525. I found one at Autohaus Arizone for $277. http://www.autohausaz.com/bmw-auto-parts/

Note: You'll still need to deal with your head gasket issue.

I think the 735iL (even in 1990) is the standard E32 with an M30 engine. It'll have a fan on a clutch to cool the radiator, but then an AC fan in front of that. I wouldnt rely on the AC fan to cool that "Big Six" engine.

I have a 92 735iL and as soon as I found a huge amount of steam coming out of the tailpipe and running rough, I went ahead and replaced the head gasket (and camshaft, and a few rockers, and a few valves) at 197500 miles.

If you dont want to do the work yourself, you'll probably pay near $1500 or more. Either way, get it done. Trust me on this. That block is almost bulletproof but that head gasket IS going to fail at some point.

I have a 1998 740il that I recently changed out the expansion tank as the spout that lead into the hose to the radiator had broken off in the hose. After the change and refill, I drove the car to work and home. After pulling into the driveway, I opened the hood to find steam coming out of the radiator (but only on the side adjacent to the expansion tank). Any ideas?