Rick's Free Auto Repair Advice

Head gasket failure

What causes head gasket failure?

Head gasket failure is far more common on late model vehicles with aluminum engine blocks and cylinder heads. A head gasket failure can result in a check engine light caused misfires, loss of coolant, loss of oil, coolant in the oil, coolant overflow at the radiator or recovery bottle, or bubbles in the coolant.head gasket

The #1 cause of head gasket failure is overheating due to low coolant, lack of proper maintenance, installation of improper coolant, incorrect ignition or valve timing, faulty radiator fans or fan relays, clogged radiator fins (exterior), crud buildup inside the radiator, restricted air intake at the grille, missing or broken air dam below the front bumper.

Worn antifreeze can cause head gasket failure

Many late-model vehicles were factory filled with long-life coolants that can last as long as 5-yrs. or 100,000 miles. Antifreeze isn’t in your engine just to prevent freezing. It contains many additives that wear out over time. The most important antifreeze additive is a corrosion inhibitor. Antifreeze in a modern engine comes in contact with many dissimilar metals in the radiator, engine, heater core, steel tubing, water pump housing, impeller, and bearing. When a liquid flows between dissimilar metals it produces electrolysis, the movement of some metal from one surface to another. So antifreeze is designed to “passivate”  the metal surfaces from the antifreeze electrolyte.

Antifreeze also contains water pump lubricant additives and anti-foaming agents. When new, antifreeze prevents electrolytic action and corrosion. However, if you exceed the useful life of antifreeze you get corrosion that can eventually plug the radiator fins and the cooling ports in the head gasket, resulting in overheating. The corrosion deposits also coat the walls of the water jacket and eat away at the water pump impeller, reducing its ability to circulate the proper amount of coolant to maintain proper engine temperature. See the clogged port in this photo?

engine coolant corrosion near head gasket

Clogged cooling port in head gasket

That corrosion dramatically reduces antifreeze flow to the cylinder head.

head gasket failure from worn coolant

Typical head gasket

What does overheating have to do with head gaskets?

The cylinder head is bolted to the engine block with special torque-to-yield bolts. TTY bolts are designed to reach a specified torque and then stretch slightly. Think of TTY bolts like a bungee cord that holds the cylinder head in place. Overheating causes the cylinder head to expand at a different rate than the engine block. The expansion causes the engine block deck and cylinder head face to develop a slight wave. Plus, the irregular expansion rates can stretch the bolts beyond their design maximum, causing leaks. Those leaks can be the cooling jacket to the exterior, cylinder to cooling jacket, coolant to oil, oil to exterior, and cylinder to cylinder.

Symptoms of head gasket failure

Head gaskets can fail between the cylinder and cooling jacket

Air/fuel or exhaust gasses are forced into the cooling system, causing overheating, bubbles in the radiator or recovery bottle, and coolant overflow.

Head gasket can fail between the cylinder and the cooling jacket

Antifreeze accumulates in the oil pan, low coolant, overheating, engine destruction

If antifreeze enters the combustion chamber, symptoms include white smoke from the tailpipe, excessive coolant usage, overheating, misfire, low power.

Head gasket can fail between the cylinder and the oil return port

Air/fuel or exhaust gasses are forced into the crankcase, causing smoking, blow-by, low power, or misfire.

Head gasket fails between pressurized oil port and cylinder

Excessive oil in the combustion chamber fouls spark plug electrodes and causes misfires.

Head gasket fails between the cylinder

Misfire, rough idle

Head gasket fails at the outer edge of the cylinder head

Oil leaks to outside of the engine

Antifreeze leaks to outside of the engine

Radiator and water pump induced failures

Most late-model vehicles use at least one electric radiator fan. Many times the radiator is equipped with two fans or multi-speed fans. Any reduction in fan speeds can reduce cooling and cause overheating. The reduced cooling can also be caused by debris (bugs, leaves, road grit, and dirt) buildup on the radiator fins—anything that reduces airflow across the radiator.

How to test for a bad head gasket

Shops use multiple methods to test for head gasket failure. Some can be performed by DIYers, others require special tools:

1) Check for coolant in the oil
2) Check for oil in the coolant
3) Pull the spark plugs and look for signs of coolant
4) Do a compression test. If the head gasket has failed between a cylinder and either the cooling jacket or oil port, the affected cylinder will show little to no pressure
5) Perform a cylinder balance test. Cylinder balance can detect all type of head gasket leaks, especially cylinder to cylinder,
6) Perform an exhaust gas test in the coolant. Using a chemical mixed with coolant, traces of exhaust will change the color of the liquid.
7) Pull the upstream oxygen sensor and look for signs of coolant contamination (for cases where the coolant is leaking into a cylinder and being burned during combustion)

How to repair a head gasket

The correct (and permanent) way to fix a leaking head gasket is to remove the cylinder head and resurface it. Then install a new head gasket with new head gasket bolts. Depending on the engine, that can cost between $1,100 and $1,800 at a shop. No wonder people want to try a head gasket sealer first.

Can a head gasket sealer fix a head gasket?

Head gasket sealer can sometimes seal a very small leak. However, by the time a head gasket fails to the point where you have white smoke billowing out of the tailpipe or exhaust gasses in the radiator, the head gasket is too damaged to be fixed with a pour-in sealer.

On a major failure, head gasket sealer usually does not work, and if it does, it’s not a permanent fix.

See this post for more information on head gasket sealers this post

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Posted on by Rick Muscoplat

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