Oil should never be present in a car’s cooling system. It is a symptom of a serious problem, such as a leaking head gasket, that is potentially costly and time-consuming to repair and even more hazardous to ignore. While serious problems, such as a head gasket issue, are repairable if immediately addressed, they can permanently and irreversibly ruin the engine if ignored. Occasionally, vandals and pranksters will pour oil into a coolant system, which can be repaired by flushing the coolant and replacing the fluid.
Look inside the reservoir and the fluid under the radiator cap. Oil may appear as a brown, grimy substance that floats near the surface.
Inspect the cooling system hoses. Oil that has run through the coolant system for an extended period can weaken its hoses.
Check for additional symptoms of head gasket failure. Other signs include overheating, white smoke in the exhaust, sweet-smelling exhaust, loss of coolant and an engine that runs roughly.
Allow the engine to cool before beginning to flush the coolant. Use disposable gloves and keep rags nearby in case of spills.
Position a bucket or catch pan underneath the radiator drain plug. Remove the plug. Remove the radiator fill cap to allow airflow during the draining process. Empty the coolant reservoir with a siphon. Evaluate the drained fluid for the presence of oil.
Replace the drain plug and radiator cap. Fill the system with tap water. Start the engine and allow it to reach a regular running temperature. Allow the engine to run for a few minutes after the fan starts, and then turn the vehicle off. Allow the engine to cool. Repeat Step 2.
Replace the drain plug and radiator cap. Fill the system with distilled water. Turn on the engine. Remove the drain plug. Pour new distilled water into the engine as it drains. Continue until the water circulates without discoloring or gathering debris. Allow the water to fully drain, and replace the drain plug.
Fill the system with the proper coolant mixture and replace the radiator cap.
