bimac
04-12-2004, 03:23 PM
I have a 1990 535i (M30 3.5L). A couple of years back, I noticed that my temp gauge had dropped from it's usual 1/2 way mark to the top edge of the blue area. I immediately assumed that I had a broken thermostat. I was on the road, so I had to go to the nearest dealership for a thermostat replacement.
Following the thermostat replacement and lengthy bleeding process (which is typical with an M30), the temp gauge was once again reading at about the 1/2 way mark (as it should be). About 3 weeks later I noticed that the gauge was again into the blue. At that point I was home. On the outside chance that I had received a defective thermostat, I purchased and installed a new thermostat and repeated the bleeding process. Once again, all was well. The gauge resumed it's rightful position at the 1/2 way mark. About 3 weeks passed, and my gauge dropped back into the blue. At that point, I knew that it couldn't be a thermostat, so I had a trusted friend and shop owner check the temperture of the thermostat housing. It turned out that the engine was at normal operating temperature. The friend suggested that the gauge might need replacing, but discouraged my doing so until there was a better reason for getting behind the dash.
Fast forward 2 years. My water pump (which was original at 199,000 miles) seizes up. I replaced the water pump, bled the cooling system, and wouldnt you know it, the gauge began reading at 1/2 way for the first time in 2 years. I was elated. I thought that maybe some anomaly with the water pump had been the problem all along .... until 3 weeks later when the gauge went back into the blue. Now, it seems to me that a bad gauge would not function correctly for 3 weeks following the cooling system being open. At this point, I am stumped.
Any help is appreciated.
Following the thermostat replacement and lengthy bleeding process (which is typical with an M30), the temp gauge was once again reading at about the 1/2 way mark (as it should be). About 3 weeks later I noticed that the gauge was again into the blue. At that point I was home. On the outside chance that I had received a defective thermostat, I purchased and installed a new thermostat and repeated the bleeding process. Once again, all was well. The gauge resumed it's rightful position at the 1/2 way mark. About 3 weeks passed, and my gauge dropped back into the blue. At that point, I knew that it couldn't be a thermostat, so I had a trusted friend and shop owner check the temperture of the thermostat housing. It turned out that the engine was at normal operating temperature. The friend suggested that the gauge might need replacing, but discouraged my doing so until there was a better reason for getting behind the dash.
Fast forward 2 years. My water pump (which was original at 199,000 miles) seizes up. I replaced the water pump, bled the cooling system, and wouldnt you know it, the gauge began reading at 1/2 way for the first time in 2 years. I was elated. I thought that maybe some anomaly with the water pump had been the problem all along .... until 3 weeks later when the gauge went back into the blue. Now, it seems to me that a bad gauge would not function correctly for 3 weeks following the cooling system being open. At this point, I am stumped.
Any help is appreciated.