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How to Check a Head Gasket

by KevinM

The head gasket is a thin sheet of relatively pliable material that sits between the cylinder head and the engine block of an internal combustion engine. Because of its position in the engine, this gasket must seal the top part of all of the cylinders while also sealing the flow passages for engine oil and coolant. Gaskets are often made from steel or composites of mineral fibers and polymers. Occasional head gasket failures can still occur despite their durable material, and savvy vehicle owners should learn how to recognize the associated signs and symptoms.

Analyze the vehicle's performance over time. A leaking head gasket can result in oil or coolant leaking into the engine cylinders which, in turn, can cause spark plug fouling and poor engine performance. A blown head gasket can also lead to low compression in one or more of the cylinders, which can cause rough engine operation. If the vehicle is running hotter than usual, has recently lost power or is running rough, this can be symptomatic of a leaking head gasket.

Remove the spark plugs individually and check for fouling. If all the spark plugs are fouled, this is likely the result of poor engine tuning; however, if only one or two are fouled, this may indicate a leaking head gasket.

Open the hood and locate the joint between the engine block and the cylinder head. On newer model cars, you may have to remove the engine cover in order to see the complete cylinder head. Examine the joint for signs of leaking engine oil or coolant, both of which denote a leaking head gasket. Start the engine and examine the joint for signs of escaping engine exhaust gases. Note that minor leaks at the head gasket joint can also be the result of improper tightening of the engine cylinder head.

Park the vehicle and wait for the engine to cool down. Open the hood, remove the radiator cap and examine the cooling fluid inside. The coolant should be greenish in color and have a clean appearance. If the coolant is brownish, or if you see oily scum or foam floating on the surface, this is a sign that engine oil is leaking through the head gasket and mixing with the coolant. With the radiator cap removed, start the engine and allow it to warm up until the thermostat opens and the coolant begins to circulate through the radiator. Examine the circulating coolant for bubbles of exhaust gases. If you see bubbles mixed in with the coolant, have an assistant rev the engine a few times and watch to see if the bubbles increase. These bubbles are a sign that exhaust gases are leaking through the head gasket and mixing with the coolant.

Turn off the engine, pop the hood and pull out the oil dipstick. Examine the oil on the end of the dipstick to see if there is light-colored froth or foam. This foam, if present, is a result of cooling fluid leaking through the head gasket and mixing with the oil.

Examine the vehicle tailpipe exhaust while the engine is running and look for signs of smoke. Do not confuse smoke with the normal water vapor that is visible in the exhaust while the engine is warming up. Bluish smoke, accompanied by an oily smell, indicates that engine oil is leaking into the engine cylinders. This can be due to a head gasket leak, or possibly leaks associated with valve seats or other internal engine parts. A whitish smoke is caused by cooling fluid leaking into the cylinders and is almost certainly caused by a leaking head gasket.

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