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What Causes a Blown Head Gasket? Can It Be Prevented?

An engine's head gasket.

So you just got the news from your shop that your trusty daily driver may be down for the count and you’ve got a failed head gasket. You’ve probably heard it can be an expensive repair, but do you know what causes a blown head gasket? Here’s what your head gasket does to keep your engine running smoothly, common causes of a faulty one and what you should do if you suspect something is wrong.

What Is a Head Gasket?

A head gasket is a relatively straightforward part. It’s basically a seal that sits sandwiched between the engine block and the cylinder head. While the cylinder head and the engine block may look perfectly smooth, there are minor imperfections that prevent a perfect seal so you can’t just bolt them together.  The head gasket doesn’t look like much, but it’s one of your engine’s essential components. It can be a simple steel gasket, or a complex composite with multiple layers and materials.
Blown Head Gasket
The head gasket does two things. First, it creates a seal to keep the internal combustion process contained. Second, it keeps coolant and oil from mixing as they circulate through your engine near each other. Both of these jobs require dealing with extreme temperatures and pressures at the same time.

Getting to a head gasket can be tricky and that’s what makes this a difficult repair. Replacing it means removing the engine’s head, which is a challenging job that’s not for everyone. Each cylinder head has its own cylinder head gasket. Depending on the layout of the engine  typically there may be one or two head gaskets. For example an inline 4-cylinder engine has one head gasket, while a V 8-cylinder engine has two head gaskets.

What Causes a Blown Head Gasket?

There are several possible causes for what causes blown head gasket failure, including engine age, but two common culprits are overheating and preignition issues.

1. Overheating: When an engine overheats, the metal expands and pinches the head gasket so it no longer seals properly. A telltale sign of this problem is white smoke coming from your exhaust, which is from coolant leaking around the head gasket. It only takes

2. Pre-Ignition Problems: If the timing of the combustion process is off even slightly, it can send too much pressure into the cylinder head. Also known as “pinging” or detonation this puts added strain on engine parts and can cause the head gasket to fail. If this happens, you may notice the car running roughly, especially when you first start the engine or at idle. You may also hear something that sounds like coins rattling in a tin can under acceleration.

Preventing a Blown Head Gasket

The best way to prevent a blown head gasket is to ensure your coolant system is functioning properly. Start by checking the radiator and the coolant overflow tanks whenever you check the oil. While you’re under the hood, inspect the radiator hoses, too. If there are splits, frays or any signs of damage, get them replaced promptly. Check your coolant mixture and change it according to your owner’s manual. While some coolant may be “long-life” they should still be tested and replaced when worn out.

Also, take note of any leaks under your car. If you see a puddle of coolant or if you find yourself refilling the coolant frequently, those are signs of an issue with your coolant system that need to be addressed. Don’t keep driving thinking you can just keep topping off a coolant leak, as it can quickly become a major coolant leak.

If you constantly hear pinging from detonation there are a few things to check. Make sure you are using the correct fuel octane level. Check the knock sensor for proper function. If you have an older vehicle with a distributor check that the ignition timing is set correctly and that the  timing advance (either mechanical or vacuum) is working smoothly.

What Should You Do if You Suspect a Blown Head Gasket?

If you think you have a blown head gasket, you should get it repaired as quickly as possible. Stop driving the vehicle immediately. A blown head gasket left alone can cause additional engine damage that will only add to your repair costs. Coolant mixing with oil will destroy bearings and any other parts that rely on engine oil for protection. Exhaust gases entering the cooling passages can over-pressurize the cooling system leading to coolant loss and accelerated overheating. Don’t wait it out if you suspect a failed head gasket.

Should You Fix A Blown Head Gasket

There are a few factors in this decision. First is the value of the vehicle. Check online and get a good idea what the value of the vehicle is on the open market. Now get an estimate for how much your local shop will charge to fix the bad head gasket. Remember that some engines have two cylinder head gaskets, and it is wise to replace both at the same time. If the cost to repair the head gasket is more than half of the value of the vehicle, it may not make sense to fix it. If you are wondering why it costs so much to fix a head gasket, the process can be quite labor intensive. If you are a reasonably capable DIYer the job can be done at home, but may still require rebuilding or replacing the cylinder head.

Check out all the engine parts available on NAPAOnline or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on what causes blown head gasket failures, chat with a knowledgeable expert at your local NAPA Auto Parts store.

Photo courtesy of Wikimedia Commons.


Nicole Wakelin View All

Nicole Wakelin covers the automotive industry as a freelance journalist for a variety of outlets. Her work includes news pieces, podcasts, radio, written reviews, and video reviews. She can be found in The Boston Globe, CarGurus, BestRide, US News and World Report, and AAA along with lifestyle blogs like Be Car Chic, The Other PTA, and She Buys Cars. She is active on social media with a large following on both Twitter and Instagram and currently serves as Vice President of the New England Motor Press Association.

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