Auto Repair Q&A



Cooling System










Auto Repair Products

Head Gasket Repair

by Aaron Turpen

Head gasket repair is costly. This is because of how much work is required to tear the engine down to the gaskets, replace them, and then put it all back together.

What Is a Head Gasket?

The head gasket is what seals the engine block and the cylinder head(s) together. Most engines have two, with the engine set up in a V-shaped form (one head on either side of the block). Some have one cylinder head down the center of the block.

The way an internal combustion engine works is to burn fuel and air in the cylinder. The timing of fuel, air and spark are determined by the rotations of the crankshaft at the center of the engine. That turns a timing belt or chain that turns the cam shafts at a given speed relative to the crank, The bumps on the camshafts determine when cylinder valves open and close to allow air and fuel into the cylinder. At the same time, the turning of the camshaft controls the distributor and sends spark to each cylinder into which air and fuel have been injected. As each cylinder burns, the push continues turning the crankshaft and the process continues up and down the cylinders in sequence.

Head Gasket Replacement

When the head gasket must be replaced, most of the engine must be torn down and removed in order to access the gaskets. The air intake, fuel injectors and rails, timing belt, camshafts, and then cylinder heads must be removed. This is roughly the top half of your car's engine core. Once removed, the gasket surfaces on both the engine block and the cylinder heads must be thoroughly cleaned and tested for ìtrueî (straightness, checking for warpage). Then the new gaskets are put on and the entire engine is put back together, paying close attention to cylinder head bolt torque, placement, and tightening order.

A competent mechanic will require 8-12 hours to remove and replace head gaskets on most 4 or 6 cylinder engines.

How To Tell If the Head Gasket Has Gone Bad

The head gasket keeps fluids separate during the combustion process. It must allow for some flexibility between the cylinder heads and the engine block, but not enough that air, fuel, coolant, or oil can mix as they flow through various parts of the block and heads. When the gasket is compromised, leaks of these fluids occurs and is needed.

The most common sign is the burning of engine coolant (anti-freeze). This will emit from the exhaust as white, sweet-smelling smoke. A noticeable loss of coolant over time will also be seen.

Sometimes, the engine will run roughly despite not appearing to burn any coolant. This is common when the seal compromise is towards the outside of the cylinder head and/or near the fuel rails. In this case, the engine is losing compression because of an air leak from one cylinder where the gasket break has occurred. A visible burnt spot where fuel has been burning through the break may also be noted in some cases.

Replacing the gasket is a huge job that requires a lot of specific knowledge. Only very advanced DIY mechanics should try this.

photo by Lewis Collard

Related Articles