Bmw 1991 525i heating problem while driving 10 to 15 miles, cools down slightly when turn on the heater. If idling in garage doesn't heat up. Blown head gasket, cracked head???

hi 7785ds, sorry about the reply, the way I read your post came across as if you had a problem not having good heat, rather than an overheating concern..my bad. Yes, if the thermostat is stuck in the close position, the car would overheat. I would still recommend checking it. Also, it is possible that your water pump has a plastic impeller, which are known for coming apart when they get aged. Usually though, a water pump would make the car go into the red after driving 10-15 minutes. Remove the radiator cap carefully and slowly when the engine is cool, and take the rpms to appr. 1200-1500. look inside the tank and see if you have a constant flow of coolant. Even when cool, there should be some flow present. As far as a headgasket or cracked head, unless the car ran into the red for an extended period, I would suspect it last. One last check is to see if the fan blade clutch is engaged when first starting the car and taking off idle speed, it should be engaged for a minute or so and then disengage lockup until the engine temp reaches appr. 3/4 temp, somewhere between midway and red. Oh, and if you are using your a/c now, have a peek at your auxillary fan in the front to make sure it comes on with the a/c on. hi 7785ds, sorry about the reply, the way I read your post came across as if you had a problem not having good heat, rather than an overheating concern..my bad. Yes, if the thermostat is stuck in the close position, the car would overheat. I would still recommend checking it. Also, it is possible that your water pump has a plastic impeller, which are known for coming apart when they get aged. Usually though, a water pump would make the car go into the red after driving 10-15 minutes. Remove the radiator cap carefully and slowly when the engine is cool, and take the rpms to appr. 1200-1500. look inside the tank and see if you have a constant flow of coolant. Even when cool, there should be some flow present. As far as a headgasket or cracked head, unless the car ran into the red for an extended period, I would suspect it last. One last check is to see if the fan blade clutch is engaged when first starting the car and taking off idle speed, it should be engaged for a minute or so and then disengage lockup until the engine temp reaches appr. 3/4 temp, somewhere between midway and red. Oh, and if you are using your a/c now, have a peek at your auxillary fan in the front to make sure it comes on with the a/c on.

If you have a cooling system pressure tester, remove the spark plugs with the enging cold. With the spark plugs out, pressure test the cooling system to 15-17 psi and leave the tester on for 30 minutes to 1 hour. If the system leaks down, keep pressurizing it. After the 30 minutes or so, look in the plug holes and see if there is any coolant in any cylinder. If there is then either the gasket is blown or the head has a crack. This is the last test I know that is accurate enough. The only other test without removing the head is with a cylinder leakdown test. If you have a cooling system pressure tester, remove the spark plugs with the enging cold. With the spark plugs out, pressure test the cooling system to 15-17 psi and leave the tester on for 30 minutes to 1 hour. If the system leaks down, keep pressurizing it. After the 30 minutes or so, look in the plug holes and see if there is any coolant in any cylinder. If there is then either the gasket is blown or the head has a crack. This is the last test I know that is accurate enough. The only other test without removing the head is with a cylinder leakdown test.