intermittent over heating - United Bimmer Community

**windinmyface2** · 09-10-2007, 10:01 AM

Hello, I have a 1996 328I I have owned for about 6 months now. About a month ago it over heated. I got home, it said check coolant, but couldn't find anything wrong. It didn't over heat again for about three weeks, said check coolant again, nothing wrong, again, then ran ok for about a week, then overheated each day, so I took it to the dealer to run a test on it, they kept it three days, tested it, and drove it, and let it idle, and could find nothing wrong. I drove it a few days, then I drove it to the store, came out after about 20 minutes, and it over heated again, and didn't want to start for about three tries, then started, and I got home. I checked it, added just alittle water, and it was ok again. I forgot to mention, when it over heated earlier, it doesn't want to start. it will start, and die a few times, before finally starting. Is there some kind of saftey switch on the car? Please help. I am afraid to drive it any where.

drz · 09-10-2007, 10:16 AM

Wow -- did it overheat into the red part of the gauge? Because, as far as I know, the engine management will not allow the car to run once it gets that hot.

Is your auxiliary fan working? When they tested it at the dealer, did they run the air conditioning?

Does it overheat when you idle, or when you are moving?

You may have a faulty thremostat that is restricting flow of coolant through the system.

How long ago did you change the coolant, thermostat, and water pump?

Auto or manual?

Please give us this info to help you diagnose the problem.

**catalyst** · 09-10-2007, 10:31 AM

Is it losing coolant?

Does hot air blow when you turn the heat on?

Does it overheat at idle or while driving?

How old are all the components?

Are you sure that the car was bled correctly? (no air in the system)

**windinmyface2** · 09-10-2007, 10:38 AM

Hi, thanks for the reply. It has hit the red, some times just to it, which the manual say's it can go to the red, and be normal. The dealer said the fan was working, I don't know if they ran the AC, they just said they would run a test on the coolant system. It over heats more at stopped, or slow speeds, but maybe will run ok for day's. A few times when it has over heated, some coolant has come out of the over flow bottle, onto the ground. It was serviced about 8 months ago right before I bought it, I'm not sure what was done, but new battery, and brake check. The coolant looks new, but not sure if the water pump has ever been replaced. It is an automatic, 6 cylinder. I had been told if they over heat because of the thermostat, to replace the thermostat, and water pump at the same time, because the plastic impeller on the pump can then spin on the shaft, and not pump the water properly. I was wondering if it has the plastic impeller, if it might be holding sometimes, and maybe free spinning, and not pumping good at the times it over heats, just a guess. Thanks again

**catalyst** · 09-10-2007, 10:41 AM

the fact that it overheats more at lower speeds could mean the waterpump is going, more revs = faster spinning waterpump and more coolant flow.

Find out if the blower still blows hot air when you start the car up and let the engine warm up. If it never blows hot that means the thermostat is stuck closed.

**windinmyface2** · 09-10-2007, 10:44 AM

Hi, thanks for replying. I don't know how old the components are, or if it was bled, or when. It has had alittle coolant come out of the over flow bottle a few times when it over heated. It over heats more at slow speed, or idle, and I didn't try the fan on the heat setting, but I will. What would that mean, a blocked heater core, or something else. Thanks again.

**catalyst** · 09-10-2007, 11:07 AM

You can tell whether or not the thermostat is opening. No hot air means coolant never circulates which means the thermostat is stuck.

Also you can feel the coolant tubing right before the thermosat for heat, again if its cold then no coolant is circulating.

Sounds like it could be a bad waterpump, an intermittent thermostat, or air in the system at this point.

**windinmyface2** · 09-10-2007, 11:12 AM

I tried holding the hose before the thermostat, it didn't get hot at idle, but after I rev'ed it, it got hot.

**catalyst** · 09-10-2007, 11:17 AM

Im going to say its the waterpump then.

I would go ahead and replace the thermostat too if you end up replacing the waterpump. Its only 30 bucks.

You could try rebleeding the system if you dont think its the waterpump, its possible there is air in it which is causing the overheat.