Head Gasket Repair and Diagnostics
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Head Gasket Repair And Diagnostics

Head gasket repair sits atop the Mount Rushmore of challenging repair jobs a technician may be faced with. Dealing with head gasket issues isn’t for the inexperienced tech. Although these jobs can bring a nice profit, the work can be complex and time-consuming. Here are some things every tech should know before tackling a head gasket repair job.


What You Need to Know About Head Gasket Repair

Head gasket repair sits atop the Mount Rushmore of challenging repair jobs a technician may be faced with.


Dealing with head gasket issues isn’t for the inexperienced tech. Although these jobs can bring a nice profit, the work can be complex and time-consuming.

Here are some things every tech should know before tackling a head gasket repair job.

Dealing with Customer Expectations 

Head gasket repair should not be approached with the mindset of “how cheaply can it be done?” Instead, find the best way to efficiently repair the vehicle so the job will last and so that all possible issues that are somewhat related can be dealt with at the same time. The only thing worse for a customer than paying a large repair bill is paying a large repair bill and then having the car act up for issues that should have been addressed previously.


Understanding the ‘Why’ of Head Gasket Failure

Why are some vehicles more prone to head gasket failures?

Sealing problems are inherent in bi-metallic engines because aluminum cylinder heads expand faster than cast-iron cylinder blocks during the warm-up cycle. The difference in expansion rates is further aggravated because the cylinder head tends to heat up much faster than the cylinder block.

The difference in expansion rates between aluminum and cast iron creates a “scrubbing” effect that eventually wears out the stainless steel “fire ring” that keeps combustion gases from entering the cooling system.

Because the cumulative effect of these repeated thermal events results in failed cylinder head gaskets, most aftermarket gasket manufacturers have designed head gaskets using space-age materials that resist scuffing wear in bi-metallic applications.

Head Gaskets

Initial Diagnosis 

The first indications of a failing head gasket are usually the slow loss of coolant with no visible leaks, the presence of a Check Engine light with cylinder misfire codes, and/or an overheating engine.


If the engine gets too hot, the cylinder head can swell to the point where it crushes the head gasket (usually between the cylinders because this is the thinnest point). The extruded material and/or cracked combustion armor then provides a leak path for coolant and/or combustion gases.

The Onboard Diagnostic II (OBD II) system should detect any misfires that occur due to a loss of compression or from spark plugs fouled by coolant seeping into a combustion chamber. So, if you find a cylinder misfire code, check the spark plug for coolant fouling, and do a compression or leak-down test on the cylinder to find out what’s going on. Internal coolant leaks caused by a leaky head gasket can usually be diagnosed by pressure testing the cooling system.


A head gasket that failed because of overheating or a hot spot will be crushed and measurably thinner in the damaged area when checked with a micrometer. By comparison, a head gasket that has failed due to detonation or pre-ignition will usually have cracked armor around the combustion chamber, which leads to burn-through.

A Word on Proper Head Gasket Repair Due Diligence

If a customer comes in with a leaking head gasket caused by an overheating engine, simply replacing the head gasket may cure the leak, but the underlying cause that made the engine overheat in the first place also needs to be diagnosed and repaired. Otherwise, the newly installed head gasket will suffer the same fate the next time the engine overheats.

Head Gasket

Head Gasket Repair Tips

Here are some tips to help avoid making any head gasket repair mistakes that could prevent the gasket from sealing properly and the engine coming back to you.


• After removing the old head gasket, carefully remove any residue from the head and block using a gasket removal chemical and scraper. Do not use an abrasive pad in a drill to whiz off or clean the head or block surfaces. Doing so may also remove metal and create shallow depressions that can prevent a new head gasket from sealing.

• Do not use any type of sealer on a head gasket unless the installation instructions that come with the gasket specifically state a sealer is required. If it is, use the type of sealer specified by the manufacturer and follow the application instructions to the letter.


• If the cylinder head has been resurfaced, check bolt lengths to make sure they don’t bottom out in blind holes. A bolt that bottoms out will apply little to no clamping force on the head, which may allow the head gasket to leak. To compensate for resurfacing, you may have to install hardened steel washers under the bolts to raise them up, or use a copper head gasket shim to restore proper head height.

• Look up the latest head bolt tightening specifications and procedures, as service procedures may have changed or been revised.

• Use an accurate torque wrench and angle gauge (if required) and follow the recommended tightening sequence to make sure the head gasket is loaded evenly when you install the cylinder head. Mistakes with this step can lead to uneven loading that results in a poor seal and leaks.


• As a preventive measure, add a dose of cooling system sealer to the coolant when you refill the cooling system. Also, make sure any bleed valves are open while refilling the system so you don’t end up with air pockets that may cause the engine to overheat. You may have to start the engine and allow it to warm up to operating temperature, then shut it off, allow it to cool and recheck the coolant level to make sure there are no air pockets.

• Make sure any factors that may have caused the original head gasket to fail have been identified and corrected so the newly repaired head gasket won’t suffer the same fate. Make sure the cooling system is functioning normally and holds pressure. Make sure the engine doesn’t knock or ping under load, and make sure the vehicle owner is using the correct grade of gasoline (premium if required).

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