How to Tell if the Head Gasket or Water Pump Leaks Antifreeze

by John Stevens J.D.

The extend of the damage caused by an antifreeze leak depends on where the leak is coming from. If the leak comes from the water pump, the problem is more of an inconvenience rather than a major undertaking, as the radiator will have to be periodically replenished with antifreeze to prevent the engine from overheating. If the leak is caused by a defective head gasket, the engine’s oil will be contaminated and the gasket should be immediately replaced to avoid engine failure.

Step 1

Twist the radiator cap off of the radiator once the engine is cool and observe the level of antifreeze in the radiator by looking through the radiator cap opening. The antifreeze level should be approximately one inch from the top of the radiator. Add antifreeze if the level is low, then install the radiator cap.

Step 2

Drive the vehicle until the engine is at normal operating temperature, then park the vehicle and allow the engine to cool. Check the antifreeze level within the radiator and observe whether the radiator has lost antifreeze. If the level has not declined, a water pump or cylinder head leak is unlikely.

Step 3

Inspect the water pumps for signs of leaks. A water pump leak will appear on the exterior of the water pump. Pay particular attention to the area where the lower radiator hose connects to the bottom of the water pump, and to the area where the heater hose connects to the pump. If either area is wet, tighten the clamp that secures the leaking hose to the water pump with a screwdriver. If the leak persists, the bearing in the water pump is likely to be defective and the water pump must be replaced.

Step 4

Attach a cooling system pressure pump to the radiator cap opening on the radiator . The pump features a single hose and a gauge. The end of the hose attaches to a metal fitting, which looks similar to a radiator cap. Twist the fitting onto the radiator cap opening.

Step 5

Actuate the pressure pump until the needle on the pump’s gauge reads within the green portion of the gauge.

Step 6

Start the engine and watch the needle on the pressure gauge. If the needle fluctuates rapidly, the cylinder head gasket is defective and must be replaced. If the engine is equipped with two cylinder heads, it will be necessary to determine which of the two head gaskets is defective.

Step 7

Remove one spark plug wire at a time from its spark plug while monitoring the needle on the pressure gauge. If the needle on the gauge steadies with the spark plug wire removed, the head gasket for that cylinder head is defective. If the needle continues to fluctuate, plug the spark plug wire onto its spark plug, then repeat the test with the next spark plug wire until the needle stops fluctuating. If removing each of the spark plug wires for one cylinder head does not steady the needle, the remaining cylinder head gasket is defective.

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