More of this Feature • Avoiding head gasket failure, and more • Dealing with high oil pressure, and more • PMY Tries... 303 Fabric Cleaner
Related Resources • Maintenance Q&A Index

What are the causes of head gasket failure, and what happens when this occurs? H.G., via e-mail
The cylinder-head gasket is the seal between the cylinder head and block; it separates air, coolant, combustion gases, and engine oil regardless of temperature or pressure. Thus it must be resistant to both the thermal and chemical products of combustion while being able to stand up to the dynamic forces generated by an engine under normal operation.

Normally this is not problematic. However, if your engine overheats, the resulting expansion and thermal load can stress the gasket beyond its limits. This is especially true of an aluminum head, as it will expand two to three times as much as a cast-iron one. The result of too much expansion can be a warped cylinder head, a loss of clamping force between the head and block, and leakage.

A leak is bad news. Coolant can leak out of coolant passages and into the cylinder and/or outside environment. Likewise oil. Compression can suffer as air in the cylinders is lost. Cooling efficiency further degrades, causing deformation to the block and liners. Lube oil thins and is less able to protect the engine’s internal components against friction and wear. In short, catastrophic engine failure will occur if the problem isn’t fixed quickly.

While overheating can destroy cylinder head gaskets, they also often fail for no apparent reason. Obviously, maintaining your engine’s cooling system is important. Make sure all components are on your maintenance list, including thermostat, zinc pencils, coolant level, expansion tank cap, pumps, hoses, and clamps. Beyond that, look for signs of gasket failure such as coolant loss, overheating, and poor performance. The sooner you correct the problem, the less likely you’ll suffer severe engine damage.

What’s the best way to lay down a good bead of caulk? E.L., via e-mail
Slow and careful best describe how to approach any caulking job. If you prefer to push the caulking gun as you lay down the bead, cut a chisel point by making two 45-degree cuts on the spout tip and hold the gun at a 45-degree angle. If you prefer pulling the gun, cut the spout on a 45-degree angle and hold the gun at a 60-degree angle as you lay down the bead. When you cut the tip for either application, make sure the nozzle opening is slightly smaller than the bead that is necessary for the job.

To avoid jagged lines, squeeze and release the trigger at regular intervals and wipe the tip with a rag as the residue builds up. If you’re looking for a really smooth bead, don’t use your finger to even it down. You can buy an inexpensive tool at most hardware stores that will give you a neat, clean finish.

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