Your car's head gasket (HG) is responsible for containing the heat produced during your engine's combustion cycle. It is also tasked with ensuring coolant and oil are kept separated, and coolant is prevented from entering the cylinders. When leaks occur, it is important to replace the HG since neglecting to do so can can eventually lead to extensive engine damage.
Replacing this component is a difficult job since it requires taking apart the engine. Moreover, depending on the reasons a head gasket fails, the job may entail machining the surface of the engine block (you'll learn why below). This usually requires the specialized skill and tools of a mechanic. This article will detail some of the factors that can cause a blown head gasket, and describe the task of replacing it.
Factors That Contribute To Head Gasket Failure
One of the most common reasons the head gasket begins to leak is due to thermal stress, especially when the engine overheats. To understand how this occurs, it's important to be familiar with the gasket's placement. It sits between the engine block and cylinder head. As heat rises around the engine, both the block and head expand. This pinches the head gasket, and places enormous stress on it. Over thousands of miles, the composite material from which it is made sustains wear, and ultimately fails.
Another common cause of a blown HG is a problem in the timing of the combustion cycle. Normally, the pistons inside the cylinders rise and fall in sync with the opening and closing of the intake and exhaust valves. When the timing is off, the pistons and valves may collide. This not only damages the pistons and valves, but also places strain on the head gasket. Prolonged exposure to this environment can lead to the part's failure.
When the HG fails, coolant may leak into the cylinders, leading to a number of problems. First, your engine will eventually overheat. Also, if a leak causes a loss of compression in the cylinders, your engine may begin to misfire or lose power. In severe cases, it may stall. White smoke coming from your car's tailpipe is usually a sign of a blown head gasket. It needs to be replaced as quickly as possible to avoid substantial engine damage.
Dismantling The Engine
Prior to taking apart the engine, you'll need to drain the cooling system. Then, the hoses must be disconnected, and the studs on the engine block must be loosened and removed. The timing cover, timing belt, and intake and exhaust manifolds must then be removed.
You'll notice several bolts holding the cylinder head in place. Make a note of which bolts belong to which locations on the head before removing them. Then, take the head bolts off, and lift the head from its place. If possible, have a friend help you remove the head to avoid straining your back.
It is critical to examine the surfaces of the head and block to make sure both are smooth. If either are damaged or warped, the replacement head gasket will fail prematurely due to stress stemming from thermal expansion. Assuming both surfaces are smooth, and thus machining is unnecessary, clean them before installing the replacement HG. Once the gasket is securely in place, reassemble the various parts.
The above procedure is made simpler if you have a service manual guiding you through each step. It's worth noting that even trained mechanics often refer to a service manual while performing this job.
Paying A Mechanic Versus Doing The Job Yourself
If you have visited an auto supply store or online parts distributor to buy a new head gasket, you will have noticed the component is inexpensive (usually, less than $100). However, the cost of having a mechanic replace it can exceed $1,000. This is due mostly to the amount of time and labor involved. If you choose to buy the part and install it yourself, invest in a service manual that clearly describes and illustrates the process.