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E30 318i/is, Z3 This tip applies to the E30 318i/is and the Z3 1.9 Roadster. It may apply to other models but these specific models have the same radiator and expansion tank.

After changing the thermostat in my 318is, it developed an air blockage in the cooling system that wouldn't allow coolant to flow. This resulted in rapid overheating.

Because there is no cap directly on the radiator along with the design of the expansion tank, pouring coolant into the expansion tank fills the lower radiator hose and partially fills the radiator. The coolant then overflows into the expansion tank without filling the upper radiator hose.

The solution is to disconnect the upper radiator hose at the radiator and pour the coolant directly into the hose. Continue until the coolant flows from the radiator, into the expansion tank and reaches the cold fill line or until the upper radiator hose is filled. Reattach the upper radiator hose and start the car with the cap off the expansion tank. Wait for the temperature to begin to rise. When it does, manually operate the throttle to raise the RPMs and observe the coolant in the expansion tank. Keep the RPMs up until you see either the bubbling stop or a sudden change in the coolant level. This indicates the blockage is gone. You may see a slow rise in the coolant level during this period until the blockage is cleared. However, if the coolant level rises near the top of the expansion tank, turn the car off, let it cool and repeat the process.

Paul Goldfine, goldfinep@gmail.com, BMW CCA Number: 93578