Although you may never have heard of it before, the head gasket is a very important part of your engine. To understand what the head gasket it and what it does, you first need to understand a little about how your engine works.

You probably already understand the basics of the internal combustion engine. A mixture of gasoline and air is sucked into a cylinder, where it is compressed and ignited. The resulting explosion – where the combustion part of the equation comes into play –forces the piston down. The motion of the piston moving downward creates the energy that ultimately drives the car.

Now let’s go back to that engine. When the car engine was first conceived, it was made from a single block of steel. All of the cylinders were drilled into it and the pistons and their associated machinery were attached at the bottom. The combustion or explosion took place at the top of the cylinder. The problem was that all of those combustions – being explosions, after all – could sometimes cause cracks in the steel of this original engine block design.

When the block was cracked, your car essentially became useless – that is, unless you wanted to replace the entire engine, which was both complicated and expensive. It had to be very frustrating to have such a small problem lead to such a huge repair, particularly when a crack typically affected only one of the cylinders.

Somewhere along the line, a bright engineer came up with the idea of separating the engine into two parts. The bottom of the block – still called an engine block – is pretty much the same. It’s still composed of the bottom of the cylinders, where the pistons and all of their associated machinery connect. The top of the engine – now called the cylinder head – is a separate piece of steel, sometimes two in a eight cylinder engine. Now, if the combustions cause cracks, they’re limited to the cylinder head. It’s still expensive to replace, but it’s more affordable and less complicated than replacing the entire engine.

Clearly, these two parts of the engine – the engine block and the cylinder head – have to fit together perfectly and form a vacuum, or else the engine won’t work. The seal that comes between those two parts of the engine is the head gasket.

A head gasket is very different from the gasket you may be most familiar with, which is likely the gasket on your refrigerator that creates the seal between the door and the refrigerator body. For one thing, the head gasket is usually made up of layers of materials, rather than just one type of rubber composite. The head gasket has to be strong enough to withstand the heat and pressure of the engine, yet flexible enough to allow a good seal to develop when the parts of the engine are fastened together.

The signs of a failed head gasket are different, depending on where the failure happens. The most common signs are an engine that runs rough, white smoke coming from the exhaust pipe or blue smoke blowing from the air conditioning vents. If any of these events occur, it’s time to have your car towed to your local mechanic for repairs before your entire engine is shot.