Hallmark
02-06-2007, 10:24 AM
For more than a year now I've been trying to figure out where I was losing coolant. There were some weeping leaks in the radiator so I replaced it and that helped. Previous owner didn't use BMW coolant or keep good maintenance records so I replaced the water pump and thermostat, but that still didn't stop it alltogether. New hoses, etc, etc and tightened all the fittings, but there was still an unexplained loss of coolant.
It finally got to the point where there was obvious steam coming from the exhaust, hard starting, and indications of water in #3 cyl (but not in the oil) so I decided that it had to be a head gasket. I pulled the head and discovered that there were cracks in cyls 3 & 4. Had it repaired and pressure tested, put it all together, and when I started it she ran like a top...but steam was still coming from the exhaust.
It occurred to me that if the head was properly repaired and I put it all together right then the only other place that coolant could get into the engine was through the intake. The process of pulling it all apart and putting it back together made me realize for the first time that there is a water jacket around the throttle body (which is made of aluminum like the radiator). I pulled the hoses off the throttle body and capped them. Viola! The steam is gone and there seems to be no additional loss of coolant. Apparently the same antifreeze that breaks down the radiator is just as effective at corroding the inside wall of the throttle body. When the engine was running the venturi effect was drawing coolant out of the water jacket and mixing it with the air/gas mixture.
For now I plan on just putting a union between the two hoses so the coolant can continue to circulate through the sensor on the air box (I'm not sure what this gets me). Now that she's had a valve job and new seals my car runs great and with no coolant leak! :D
Now, on to those pesky sub-frame bushings...
It finally got to the point where there was obvious steam coming from the exhaust, hard starting, and indications of water in #3 cyl (but not in the oil) so I decided that it had to be a head gasket. I pulled the head and discovered that there were cracks in cyls 3 & 4. Had it repaired and pressure tested, put it all together, and when I started it she ran like a top...but steam was still coming from the exhaust.
It occurred to me that if the head was properly repaired and I put it all together right then the only other place that coolant could get into the engine was through the intake. The process of pulling it all apart and putting it back together made me realize for the first time that there is a water jacket around the throttle body (which is made of aluminum like the radiator). I pulled the hoses off the throttle body and capped them. Viola! The steam is gone and there seems to be no additional loss of coolant. Apparently the same antifreeze that breaks down the radiator is just as effective at corroding the inside wall of the throttle body. When the engine was running the venturi effect was drawing coolant out of the water jacket and mixing it with the air/gas mixture.
For now I plan on just putting a union between the two hoses so the coolant can continue to circulate through the sensor on the air box (I'm not sure what this gets me). Now that she's had a valve job and new seals my car runs great and with no coolant leak! :D
Now, on to those pesky sub-frame bushings...