With spring just around the corner, and summer soon to follow, it may be time to check your BMW’s cooling system. Problems in this area usually occur during the hot season, when extreme cooling system pressures will rupture a coolant hose that has rotted from the inside out. To avoid roadside emergencies of this nature, we recommend checking your cooling system hoses once each year, and replacing them at least every 70K miles. The perfect time for checking the hoses is just before performing your annual cooling system flush. (see "Is Your Car Running A Constant Fever?" for details.)

Before flushing the cooling system, check the components that may need replacing. Checking the system properly requires pressure testing the cooling system. This can be accomplished either of two ways. A cooling system pressure tester is designed to pump air pressure into the cooling system so that you can visually check the entire system for leaks, without the hazard of handling hot components during the inspection. If you do not have a pressure tester, there is an alternative. You bring the engine to operating temperature, and then turn the engine off. Be careful. The cooling system is hot, and water leaks can burn. The pressure that is built up in the cooling system at operating temperature helps locate any leaks.

Once the system is pressurized:

• Slightly flex each hose, paying close attention for water leaks.
• Look at each hose connection for signs of dried coolant residue (white chalky powder).
• Look under the water pump shaft (there is a small inspection hole). Water leaking from this area is an indication of a water pump seal failure.
• Check the radiator. The most common failure here is the crimped seams where the plastic tanks, and aluminum core are joined. Inspect this area carefully for signs of dried coolant residue.
• Check the heater hoses.
• Check the mating surface between the engine block and the cylinder head.

All of these areas are potential problems. If you do have access to a cooling system pressure tester, the system should hold pressure without loss for approx. 2 hours. Even the slightest leak anywhere requires repair or replacement of the failed or failing component.

Sure signs of impending hose failure:

1. Bulging hoses. If the hoses are bulging more than 1/8” immediately after the hose clamps at the radiator or water manifold, this may be a sign of broken fiber reinforcement strands inside the hose itself.
2. Slight seepage of coolant from a hose-end.
3. External cracks in the rubber of the hose itself.
4. Presence of permanent hose clamps. The Factory uses permanent, non-removable hose clamps in some areas. This indicates that the hoses are original. If your vehicle has more than 70K miles, these hoses need replacing.

Some Professional Tips

Be sure that you check all of the hoses for age. It is common practice to replace the 3, easy-to-see hoses at the radiator, leaving the remaining worn hoses under the manifold, and heater core to fail at the worst moment.

Remove one of the hoses and inspect the inside for cracks, rust and other failures. This may require squeezing the hose to visually see the cracks. Cheap insurance against unexpected failures is readily available by always using new hose clamps whenever replacing hoses.