When the engine's cooling system becomes contaminated, it should be flushed thoroughly to remove the contaminants before the engine is seriously damaged. One source of contamination that is damaging to the engine if not corrected immediately is a cracked oil gallery. With a cracked oil gallery, oil will be forced into the cooling system while the engine is operating, and when it is stopped, coolant will leak into the lubricating system. If mixed with oil in the crankcase, this antifreeze forms a varnish which quickly immobilizes moving engine parts.

To remove such contaminants from the engine, both the cooling system and the lubrication system must be thoroughly flushed after the engine is repaired.

Caution: In order to avoid personal injury, do not remove the cap or open the cooling system drains from a hot system. Allow the system to cool first.

If the engine has had a failure resulting in the contamination of the cooling system with lubricating oil, or a substance other than a recommended antifreeze has been added, the following procedure is recommended.

1. Drain the coolant. Refer to Cooling System Draining and Filling .
2. If an L61, remove the heater core inlet and outlet hoses from the engine outlets.
3. If an L81, remove the heater core outlet hose from the auxiliary coolant pump and rear inlet hose from the front inlet hose.
4. Place the end of the heater core inlet hose, the lower heater core pipe is the inlet, in a container and apply low-pressure shop air 35 kPa (5 psi) to the heater core outlet hose to blow the coolant out of the heater core.
5. Install the heater inlet and outlet hoses.
6. Prepare a mixture of Calgon® or equivalent automatic dishwasher detergent, and water at the ratio of 2 ounces, dry measure, to 3.8 liters (1 gal) of water.
7. Remove the engine thermostat to permit the Calgon® or equivalent and water mixture to circulate through the engine and the radiator.
8. Fill the cooling system with the Calgon® or equivalent solution.
9. Run the engine for 5 minutes.
10. Drain the cooling system.
11. repeat steps 8 through 11.
12. Let the engine run for 5 minutes.
13. Drain the cooling system completely.
14. Install a new engine thermostat. Refer to the Thermostat Inlet Housing and Element installation procedure in this section.
15. Install the new main water pump. Refer to the Water Pump (Unit Repair) installation procedure in the Mechanical section of this manual.
16. Use clean water to rinse away any coolant that was spilled during service.
17. Fill the cooling system. Refer to the Coolant Replacement procedure in this section.