The two main working parts of an engine are the engine block and the cylinder head. Oil and coolant passages run between the two, and the combustion chamber also lies in between.
The cylinder head gasket seals the oil and coolant passages and the combustion chamber. The combustion chamber is defined by the pistons and cylinder walls on the engine block side and the valves and spark plugs on the head side.
The valves housed in the cylinder head are operated by the camshaft, which can be in various places. The location plays a big part in determining how difficult it is to replace the head gasket.
What’s the Price of a New Head Gasket?
Let’s assume a labour rate ranging between £70 and £100 per hour to estimate the cost of replacing a head gasket on some common vehicles:
- For a 2004 Subaru Forester with a 2.5-liter engine`
The labour time to replace a cylinder head gasket is 7.5 hours, or 11.9 hours to replace both cylinder heads. The engine is a four-cylinder boxer with two cylinder heads, with camshafts in the heads run by a timing belt.
A non-OE head gasket kit and new head bolts cost about £180 (which covers both sides). Adding average machine shop and fluid costs, the total cost to complete the job would be about £705 for one head gasket or £1,013 to replace both head gaskets.
On this vehicle, additional work that might be best done at the same time is the timing belt. An aftermarket timing belt kit (with tensioner and pulleys) costs about £110, and the labour involved should be included in the cost of the cylinder head work. On the engine, there may also be a complication of resetting the valve clearances. If this needs to be done, then the labour is 2 hours per bank, and shims would be additional.
- For a 2010 Nissan Rogue with a 2.5-liter engine
The labour time to replace the cylinder head is 14.8 hours. This engine uses a timing chain with overhead cams on a conventional inline four-cylinder engine. An aftermarket head gasket costs about £75. With normal machine shop and fluid costs, this takes the job about £1,110 to complete.
Ordinarily, there is no replacement interval on a timing chain, and unless an engine has very high mileage, the timing chain would be re-used after a head gasket replacement. But on this particular engine, there is a high failure rate for the timing chain, and replacing it would be recommended while it is off for the head gasket work.
A factory timing chain set (primary and secondary) with tensioners and guides costs about £335. Some labour would be additional, but most of the labour involved generally overlaps the head gasket work.
- For a 2009 Ford F-150 with a 5.4-liter engine
In this case, the labour time to replace a cylinder head gasket is 19.9 hours for one side or 21.1 hours for both sides. The engine is a V-8 with overhead cams driven by a set of timing chains. A non-OE head gasket kit with head bolts costs about £130. With normal machine shop and fluid costs, this takes the job to about £1,523 in total cost to complete for one side and £1,607 for both head gaskets.
A new non-factory timing chain set for the Ford engine costs about £147 if warranted by engine mileage or other indicators. Almost all the labour time required for its installation would be included in the head gasket job.
- For a 1993 Chevrolet K1500 with a 5.7-liter engine
The labour time here to replace one cylinder head gasket is 8.9 hours, and the time to replace both is 12.7 hours. The engine is a V-8 with a camshaft in the engine block, so the job is relatively simpler than in other cars.
A non-OE head gasket kit and head bolts cost about £55. With normal machine shop and fluid costs, the job comes to about £680 in total cost for one side and £944 to replace both head gaskets.
On an older style engine, the camshaft is in the engine block, working the valves through pushrods that extend up to the cylinder head. In this case, the cylinder head can be unbolted and removed without having to deal with the engine timing.
On newer style engines, the cam (or cams) is on top of the cylinder head and drives the valves more directly. In order to remove the cylinder head, the camshaft has to be removed, which also means removing either the timing belt or timing chains.
If the camshaft is driven by a timing belt, it is usually made to be serviced more or less easily. If the timing is driven by a chain, it is usually not made to be easily serviceable, and the job can be difficult and time-consuming.
The head gasket is a very high-stress part. The two most common gasket types are multi-layer metal and composite, which have gasket material bonded to a steel core.
Problems of either type can come from simple ageing and corrosion, but more common are problems resulting from the warping of the cylinder head. The head is a heavy casting, usually aluminium, and is susceptible to warping from heat stress over time.
The cylinder head is held down by head bolts, which are of the “torque to yield” type, meaning they are tightened down to a specific point of stretch. When a cylinder head warps, the castings want to lift apart, and the stretch of head bolts tries to hold them together.
There is some margin for error in the gasket and the bolt forces, but gasket failure usually begins with the lifting force of a warped cylinder head overcoming the clamping force of the head bolts. Once combustion pressures or fluids begin to bypass the gasket, they can carve a path, so to speak, which then continues until the problems are repaired.
A head gasket failure can become apparent in various ways. Leaks of oil or coolant can occur externally, or they can mix internally, or they can leak into the combustion chamber.
Symptoms of that would be misfires, which can come from compression loss. However, more often, misfires come from oil or coolant leaking into the combustion chamber and fouling the spark plugs.
That’s often accompanied by combustion gases finding their way into the cooling system. Symptoms of that would be gas bubbles and pressure in the cooling system.
In other cases, oil and coolant can mix, and symptoms of that would be milky coolant-contaminated oil. There are a few different ways to figure out the problem depending on how it presents itself. One way or another, it usually winds up being about an hour of diagnostic work.
Parts of Head gasket Replacement
There is a lot involved in head gasket replacement, going with the basic dictum that an expensive job should be done once only and shouldn’t be done again for a very long time. There are many parts of the job that need to be done right.
Disassembly is an important part of the process, being the step where all the parts removed are evaluated. The job is usually diagnosed and estimated before this step, but it’s not usually possible to be certain about many of the details before disassembly.
All the various parts, accessories, wiring, and gaskets that are removed will either need to be re-installed or replaced to get the vehicle back on the road. It’s important to evaluate them as they are handled in order to know whether the initial estimate will at least possibly cover the necessary work.
Surprise issues tend to be less damaging the earlier they are known. On an involved job, some attention paid in the first part also makes the reassembly side easier.
Once the cylinder head is removed, it needs to be sent to a machine shop for evaluation. This is a step that takes an overall look at the head.
The deck is measured for trueness, the valves and valve seats are inspected, and the head is cleaned and checked for cracks. It’s normal to provide the machine shop with valve stem seals, so they may be installed when the valves are reinstalled. Usually, that’s done by the machine shop.
Resurfacing of the head is usually done whether there is a warp to it or not, as there is a specification for the tooth or roughness of the mating surface that must be met. This helps the head gasket seal properly.
Sometimes, the valves need to be lapped, and other things that might be needed are valve seats or valve guides, or sometimes, the valves themselves. In practice, the cost of getting a head ready to reinstall can be higher than that of installing a rebuilt head.
Many shops will price the job both ways; one if the head checks out OK and the other if it turns out to be cheaper to replace the cylinder head. A rough estimate for machine shop costs is about £205 per cylinder head.
The parts necessary for the job are usually provided in a head gasket kit. This typically includes the head gasket itself, the valve cover gasket and seals, the timing cover seals, the valve stem seals, and new head bolts.
Aftermarket kits are the simplest way to go, as they usually include the whole variety of seals and gaskets involved. Factory parts for the same job are harder to price out as they are usually sold individually.
There can also be dozens of individual parts that it’s easy to miss something that winds up being needed. Head bolts are the highest stress parts and generally not re-useable, but if they don’t come with a gasket kit, they are usually easy to source.
Other parts that are removed for the job are the timing belts or timing chains. They are usually replaced if there is any reason to replace them.
Timing belts are usually replaced unless near new, as they are a maintenance item with a defined lifespan. Timing chains usually have no replacement interval, but they do wear, and some are more prone to wear and issues than others.
If there is a doubt, the timing chains are usually replaced. A new timing chain or timing belt is usually installed with new guides and tensioners.
Other less-involved parts sometimes involve spark plugs or plug wires, the water pump, serpentine belts, and tensioners, etc. The general approach is that there is no reason to replace a part that hasn’t failed.
But, on the other hand, the overall goal remains to go in once and correctly do everything necessary. This way, there is no reason to have to go back in any time soon or to have to do the same job twice.
Other Ways to Do the Job
The above estimates are the basic approach to repairing a head gasket failure. Sometimes a head gasket needs to be replaced for other reasons as well.
For example, an exhaust bolt breaks off and can’t be practically removed or drilled out on the vehicle, and the head needs to be pulled to restore the threads on a workbench. In that event, the head gasket still needs to be replaced because once torqued down, it isn’t re-usable anymore.
However, the cylinder head can sometimes just be surface-cleaned and re-installed, which would make the parts and labour costs the same, but you can save on the machine shop costs.
Head bolts are best replaced rather than re-used, as the torque process stretches the bolt, then locks it into position for a prolonged period of heat cycling. A bolt, once removed, doesn’t respond predictably (or well) to the stretching process again. On the principle of doing the job once, not twice, the easiest call is to avoid the temptation to save money by reusing head bolts.
Saving costs by replacing just the head gasket and leaving the other gaskets for individual assessment and replacement as necessary is a reasonable way to save costs. In many cases, old gaskets reseal OK, and many seals are easily accessed, so saving a little cost isn’t a big gamble.