shogun
06-20-2014, 09:54 AM
1992 BMW 735iL: Overheating and lost heat same time
(excerpt of problem description and final repair solution)
One day in January (it was like 8 degrees F out) while driving down the highway I lost heat, the blower motor still blew air just no heat. Then about 30 secs later the coolant temp indicator hit red. I slowed down and got my rpms down to about 2k from 3.5k, at this point the temp went back down to normal operating temp (about 12o'clock on the dial). I reved up the rpms again and the same thing happened.
Now any time I get the rpms around 3k the temp goes up and it hits the red area. I have already replaced the thermostat, and one of the temp sensors. I am pretty sure the water pump works because after make sure the system was bled, I didn't tighten the small hose that connects the top of the radiator to the overflow tank, fluid shot out of it.
I will look in to bleeding the system again. I thought I did it right but will try one more time. The whole reason why I had the system opened was because I had this issue. Up until that I had been driving it for months with out issue.
Re-bled the system, same issue. I took apart the water valves and aux water pump. The valves looked good, however the aux water pump doesn't work. I bypassed it and got my heat back. I havn't gone for a test drive to see if it over heats, but at least I've got one problem fixed so far.
I've done some more testing and what I thought would get better made things worse. The car is still over heating with the aux water pump removed. I decided that if it was air in the system removing the thermostat would clear any air that would normally get stuck there. Normally when I idle the car it doesnt overheat, only when I drive at high rpms would it over heat. After removing the thermostat it would overheat at idle. This confused me and now I have no idea where to go. I guess two things are left , the water pump and the radiator? If I am getting heat in the cabin does that mean ther water pump is working? One thing I noticed when the car go to the red zone, the bottom part of the radiator was cold.
Well, bad news. Ive changed out the radiator, bled and re-bled the system. I get the same condition as before. I am fine at idle but anything above 2.5k rpms the temp goes up and up. It would go to redline if I let it. I am at a complete loss now. New thermostat, new radiator, I'm pretty sure the water pump is working since hot coolant is flowing through the water valves with the aux water pump bypassed.
Success! It was the water pump. The impeller was plastic and it cracked all the way to the bearing making it not tight and I could free spin it without moving the shaft. It explains everything that was wrong with the car. Went for a 36 mile drive this morning at high speeds and rpms, no more problems. BTW the new one I got has a metal impeller.
http://www.bimmerboard.com/members/shogun/crackedplasticimpellerM30.gif
Text and pic by Gold3nMAn
(excerpt of problem description and final repair solution)
One day in January (it was like 8 degrees F out) while driving down the highway I lost heat, the blower motor still blew air just no heat. Then about 30 secs later the coolant temp indicator hit red. I slowed down and got my rpms down to about 2k from 3.5k, at this point the temp went back down to normal operating temp (about 12o'clock on the dial). I reved up the rpms again and the same thing happened.
Now any time I get the rpms around 3k the temp goes up and it hits the red area. I have already replaced the thermostat, and one of the temp sensors. I am pretty sure the water pump works because after make sure the system was bled, I didn't tighten the small hose that connects the top of the radiator to the overflow tank, fluid shot out of it.
I will look in to bleeding the system again. I thought I did it right but will try one more time. The whole reason why I had the system opened was because I had this issue. Up until that I had been driving it for months with out issue.
Re-bled the system, same issue. I took apart the water valves and aux water pump. The valves looked good, however the aux water pump doesn't work. I bypassed it and got my heat back. I havn't gone for a test drive to see if it over heats, but at least I've got one problem fixed so far.
I've done some more testing and what I thought would get better made things worse. The car is still over heating with the aux water pump removed. I decided that if it was air in the system removing the thermostat would clear any air that would normally get stuck there. Normally when I idle the car it doesnt overheat, only when I drive at high rpms would it over heat. After removing the thermostat it would overheat at idle. This confused me and now I have no idea where to go. I guess two things are left , the water pump and the radiator? If I am getting heat in the cabin does that mean ther water pump is working? One thing I noticed when the car go to the red zone, the bottom part of the radiator was cold.
Well, bad news. Ive changed out the radiator, bled and re-bled the system. I get the same condition as before. I am fine at idle but anything above 2.5k rpms the temp goes up and up. It would go to redline if I let it. I am at a complete loss now. New thermostat, new radiator, I'm pretty sure the water pump is working since hot coolant is flowing through the water valves with the aux water pump bypassed.
Success! It was the water pump. The impeller was plastic and it cracked all the way to the bearing making it not tight and I could free spin it without moving the shaft. It explains everything that was wrong with the car. Went for a 36 mile drive this morning at high speeds and rpms, no more problems. BTW the new one I got has a metal impeller.
http://www.bimmerboard.com/members/shogun/crackedplasticimpellerM30.gif
Text and pic by Gold3nMAn