Rick's Free Auto Repair Advice

What causes a head gasket leak?

Most common causes of head gasket leak

The cylinder head gasket forms a seal between the engine block and cylinder head. If you have a head gasket leak, coolant can flow into the combustion chamber or air/fuel and exhaust gas can flow into the cooling system. A head gasket leak can also cause coolant to flow into the crankcase through an oil passage.

What are the symptoms of a head gasket leak?

• Coolant is always low. If the leak is between a coolant passage and the combustion chamber, coolant can flow into the cylinder where it is burned with the air/fuel mixture. Burning coolant can foul your spark plugs, cause misfires and cause permanent damage to your catalytic converter. Once you notice a pattern of low coolant, get your engine diagnosed and fixed. Do NOT continue to drive it in this condition or you’ll cause even more damage.

• White smoke from tailpipe. When coolant burns with the air fuel mixture it produces steam that the catalytic converter cannot remove, so it flows out the tailpipe. Coolant can permanently damage your catalytic converter

• Coolant in your oil. When the head gasket leak is between a coolant passage and an oil passage, coolant can flow into the oil pan where it mixes with engine oil to form a chocolate milkshake looking mess. The oil/coolant mixture can’t lubricate your engine properly and if you continue to drive in this condition, you will destroy your engine.

• Engine overheats. When the head gasket leak is between a cylinder and the cooling system, an air/fuel mixture or exhaust can be pumped into the cooling system, overheating the already hot coolant. The symptom appears as a rapid rise in engine temperature.

• Radiator hose pops off. As shown above, when exhaust gas or air/fuel enters the cooling system, it can over pressurize the system, causing the radiator hoses to pop off their fittings.

• Coolant recovery tank overflows. The air/fuel or exhaust gasses push coolant back into the coolant reservoir where it overflows and spills onto the street.

Most common causes of a head gasket leak

• Improper coolant maintenance. Engine coolant contains anti-corrosion

View of clogged radiator from the filler neck

This is what neglect looks like

additives. Once those additives are depleted, corrosion can set in and degrade the metal edges where the seals to the coolant and oil passages and cylinder. Eventually, those areas fail.

• Improper oil maintenance. The anti-corrosion additives in oil wear out over time. When that happens, corrosion sets in. That corrosion can damage the sealing areas on the head gasket, resulting in a head gasket leak.

• Overheating due to improper maintenance. As shown above, when you neglect routine coolant changes, corrosion overtakes your engine. The same type of corrosion that destroys the metal sealing rings in the gaskets also causes corrosion in the radiator. That corrosion reduces the ability of your radiator to remove heat, resulting in engine overheating. Engine overheating causes the cylinder head to warp and lose its seal to the engine block.

• Overheating due to radiator fan failure. Most engines have electric radiator fansradiator fans, although many trucks still use an engine driven fan operated by a thermostatic clutch. If the radiator fans don’t operate properly, the engine can overheat. A single incidence of overheating can cause a cylinder head to warp, resulting in a head gasket leak.

• Engine knock. Engine knock is caused by the improper detonation of the air/fuel mixture. If your engine requires high octane fuel and you fill it with a lower octane, your engine will knock. The knock sensors will detect the knock and adjust ignition timing to compensate. However, there’s a limit to home much the computer can compensate. If your engine has carbon buildup, the computer may not be able to retard timing enough to eliminate knock. The extremely high pressures produced during a knock event can damage the gasket, causing a head gasket leak.

How to avoid a head gasket leak

Stay up to date on coolant and oil changes

Use the recommended octane fuel

Clean the radiator fins to ensure full airflow

If you see an increased engine temperature, get it checked out immediately.

If you have to refill the coolant reservoir more than once per year, get the engine checked for coolant leaks or head gasket issues.

If your engine overheats, pull over IMMEDIATELY and STOP. Call a tow truck. Do NOT continue to drive. A towing bill will cost far less than the cost to repair the extra damage you’ve done to your engine by driving it while hot.

How about head gasket sealers?

Wondering if you can fix a leaking head gasket with a sealer? See this post on how head gasket sealers work and what your chances are of success

©, 2018 Rick Muscoplat


Posted on by Rick Muscoplat


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