Very strange overheating problem in my E36. Any advice/help is greatly appreciated.

[dividebyzero]

Hey everybody,

If you've read some of my previous posts, you'll know that I'm not a DIY person. Sorry if this post is too detailed/long, but I want to be as clear as possible when it comes to describing my problem so I can hopefully get some good answers. Anyway, here goes....

For the past several months I had this odd overheating problem in my E36. Sometimes, when I would start the car up again after the engine had been running not too long before and had gotten hot already (i.e. needle at halfway on temp. gauge), the car would overheat for about 10 seconds (to about 3/4 of the way toward hot on the temp. gauge) and then go back to halfway after those 10 seconds. And then one afternoon, after I'd been driving the car for a while, the needle began to inch toward hot when I was at a stoplight. Once the light turned green and I got moving, after about 5 seconds, the needle went back to halfway. Yet, both of these incidents I just described were both intermittent and I continued to drive the car for at least three weeks and would only notice either of these two every now and then.

Nonetheless, I made an appointment with my mechanic and had the car examined. He checked over the cooling system and told me that the fan clutch was bad. He said he was able to even stop the fan in front of the engine with his bare hands (that's how bad it was, he tells me). Anyway, he replaced it and I picked the car up yesterday and everything seemed normal when I would drive it. Well, just a few hours ago the same two overheating incidences from before appeared. I was running errands all afternoon and the car began to overheat briefly when I started it up after leaving a grocery store before going back to normal after 10 seconds. And then 5 minutes later, as I sat at a stoplight, the needle began to inch toward hot again. Luckily, the light quickly turned green and it went back to halfway after I started driving.

Called my mechanic and he was as dumbfounded as I was. He told me that after replacing the fan clutch, he let the car sit idle for a while and it didn't overheat at all. He also told me that he checked over the other components in the cooling system (i.e. water pump, expansion tank, etc) and everything looked fine. And there were no leaks either.

So, at this point, I'm gonna take it back to him one more time to figure what's wrong. If he tells me that he can't find anything wrong or if he does find something but the problem still persists after he fixes it, then I'm going to a different mechanic to hopefully get the problem solved once and for all. If he finds a problem, fixes it, and the overheating doesn't happen again anytime soon, then I'll still go back to him and just hope that he made a simple mistake the first time around.

Reason I'm asking people for help here is to get an idea from some of you as to what you think it might be. I will present any and all suggestions to my mechanic to see what he thinks.

Thanks everybody for your help. (My car btw is a 1998 328i with approx. 126,000 miles on it)

[Haifisch M3]

Replace the thermostat. They are supposed to fail open but I have seen them stick in the closed position which would cause the symptoms that you are describing (especially the fluctuation of temps as it suddenly opens and allows the hot coolant to flow out of the head and cooler coolant enter the head). Also make sure that the cooling system has been bled properly.

[323i E30]

Given that it cooled down when moving again, still makes me think a bad fan clutch. Is the replacement clutch OEM? If not, replace it with an OEM one.

[gmarkh59er]

It could be a head gasket issue. Is there water in the oil??

[bmwdirtracer]

I would first suggest that your mechanic seems to be doing just fine, and trying to save you money, too. As well as the fan clutch, I would also have STRONGLY recommended that you replace the entire cooling system, beginning with the thermostat and the water pump.

The entire cooling system is maintenance replacement at ~100k miles, or nine years. This includes radiator, all hoses and plastic pipes, expansion tank, cap, water pump and thermostat.

As for the temp getting a little hot after turning a warm car back on: YES, that is absolutely normal ! You have just experienced "heat soak". The water pump isn't working with the engine off; there's no air moving underhood, therefore the engine coolant temp will be going up. Once you start moving, the coolant and air move, and the engine cools.

Nonetheless, your cooling system is highly questionable, from your other symptom, and I highly recommend you begin with water pump, thermostat, maybe a couple of hoses, and some nice new blue BMW coolant.

[dworthy]

+1, if you don't know when the thermostat was last changed, it probably never was. So get both done, and have him closely inspect the cooling system. Normally the BMW radiators will start to sag at the bottom prior to failure.

[Zimmerman84]

I am having a similar nightmare my car overheats when driving, I have replaced the thermostat/thermostat housing/water pump/radiator/top and bottom radiator hoses/auxhilary belt/fan clutch and I still cant even bleed the system without it just boiling the coolant and steam coming out of the bleed screw, I get no hot air inside and was told its an air lock so I disconnected the hoses going to the heater matrix and there is water coming through but still no heat and it still overheats, once the engine is up to temperature the top and bottom radiator hose are hot and water is definatly moving around the system, I cant figure it out and I'm not going to spend anymore money on it unless I know its not completely knackered.
Its a 1999 e36 323i 142k miles, no oil in the coolant and no coolant in the oil, no excess smoke from the exhaust.

Any help would be appreciated with this.

[dworthy]

I am having a similar nightmare my car overheats when driving, I have replaced the thermostat/thermostat housing/water pump/radiator/top and bottom radiator hoses/auxhilary belt/fan clutch and I still cant even bleed the system without it just boiling the coolant and steam coming out of the bleed screw, I get no hot air inside and was told its an air lock so I disconnected the hoses going to the heater matrix and there is water coming through but still no heat and it still overheats, once the engine is up to temperature the top and bottom radiator hose are hot and water is definatly moving around the system, I cant figure it out and I'm not going to spend anymore money on it unless I know its not completely knackered.
Its a 1999 e36 323i 142k miles, no oil in the coolant and no coolant in the oil, no excess smoke from the exhaust.

Any help would be appreciated with this.

Mate, you need to start your own thread, as we cannot talk to two people at the same time with similar problems.