The patient: 1998 Z3, M52 engine, 6 cylinder, 2.8L
How the problem always starts: If I'm starting with the car completely cold, everything runs perfectly. Starts up, engine heats up to operating temp and stays steady. I've driven an hour or more at highway speed without any problem. However if I shut it off and then attempt to drive it again before it's completely cold, it begins overheating. If I it shut off for an hour or so, then it's fine.
I assumed a stuck thermostat and replaced it. This resolved the problem completely for a couple of months, then it started happening again. Talked with a mechanic family member who thought it likely I just got a dud part, so I replaced it again. Once again, zero problems for a few months, then same symptoms.
The car is old enough that the cooling system has had a fair bit of work. In the last couple years, I've replace the radiator, water pump, and most of the hoses, either in response to leaks or just, "might as well while I've got it apart." I've always run the BMW-specific antifreeze as well, and I know to bleed the system after any work.
I've searched through the forum and read through other threads on overheating, but none of them seem to have the same symptoms, or describe steps I've already taken. Anybody have any suggestions?
How the problem always starts: If I'm starting with the car completely cold, everything runs perfectly. Starts up, engine heats up to operating temp and stays steady. I've driven an hour or more at highway speed without any problem. However if I shut it off and then attempt to drive it again before it's completely cold, it begins overheating. If I it shut off for an hour or so, then it's fine.
I assumed a stuck thermostat and replaced it. This resolved the problem completely for a couple of months, then it started happening again. Talked with a mechanic family member who thought it likely I just got a dud part, so I replaced it again. Once again, zero problems for a few months, then same symptoms.
The car is old enough that the cooling system has had a fair bit of work. In the last couple years, I've replace the radiator, water pump, and most of the hoses, either in response to leaks or just, "might as well while I've got it apart." I've always run the BMW-specific antifreeze as well, and I know to bleed the system after any work.
I've searched through the forum and read through other threads on overheating, but none of them seem to have the same symptoms, or describe steps I've already taken. Anybody have any suggestions?
