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How to Race an Engine to Bleed Coolant

Racing an engine to remove air is a method used to remove bubbles of air trapped within the coolant system of an automobile after you change the coolant. In order for the thermostat to work correctly, you must purge the system of air. Otherwise, the thermostat experiences pockets of air that disrupt the heating and cooling process. If you leave this process unchecked, it could cause expensive engine damage.

Instructions

1

Remove the radiator cap from the filler spout on the radiator. If your vehicle does not have a radiator cap, lift the cap off the expansion tank for the radiator.

2

Turn on the engine, rev it to approximately 3,000 RPM until the radiator fan turns on for a period of one minute, and then turn the vehicle off. The fan turning on is an indicator that the thermostat is in the open position, circulating the coolant through the engine. The air goes to the least path of resistance. In the coolant system, that is the hole in the filler spout.

3

Check the fluid level in the radiator. The level should be slightly lower than normal. Fill the fluid to within an inch of the top of the spout.

4

Repeat step two and three a second time and then place the cap back on the radiator.