What are the Symptoms of Blown Head Gasket ?

If you are a car owner, then nothing can set a bad day/mood in motion than having a blown head gasket. The minute your most trusted mechanic utters those words, you can immediately picture the dent the repair and labor cost will do to your bank balance, not to mention the inconvenience caused. What’s more, you may start wondering what may have caused the problem or what are some of the symptoms of a blown head gasket that you may have missed or ignored.

Bear in mind that the head gasket plays a crucial function in the running of your engine. This engine component resides between your cylinder head and engine block. Gaskets help your car build up the ideal compression while keeping engine oil and coolant from leaking by sealing the engine cylinders. With that said, here are some of the symptoms or signs to look out for to establish whether your vehicle has a failed gasket.

Most Common Symptoms of Blown Head Gasket

A faulty gasket is downright one of the most critical car engine problems out there. So, how do you know whether your car has this issue? Well, any of the following symptoms below should raise a red flag and force you to consult your trusted mechanic.

what causes a blown head gasket

The Presence of Bubbles in your Radiator

A faulty head gasket can cause exhaust gases to leak into your antifreeze/coolant. As a result, you will find bubbles in your radiator, which may seem like a boiling coolant.  You can check for the existence of exhaust gases in your coolant by carrying out a DIY blown head gasket test.

Reduced Engine Power

When your head gasket has failed to the extent of compromising your combustion chamber, the compressed mixture of air and fuel escapes. This situation lowers the compression inside your engine cylinder, leading to a dramatic loss of engine power. Although this may not conclusively mean that your head gasket is faulty due to the possibility of other fluid leaks, it shouldn’t be ruled out until a trusted mechanic checks your car.

Dirty Spark Plugs

Although other engine issues can leave some small, whitish deposits on your vehicle’s spark plugs, you should be open to the possibility of a blown head gasket. These deposits are left behind when the coolant is exposed to extreme heat inside the combustion chamber. Check around the electrode or ground strap of your spark plugs for any signs of such deposits.

Overheating Car Engine

Although an overheating car engine can be caused by several factors, including a faulty cooling fan or leaking antifreeze, it could also be due to a bad head gasket. Mostly, this problem occurs due to inadequate coolant as a result of leaking into the combustion chamber, where it is turned into steam. If this problem is not looked into immediately, it can lead to other engine problems, such as warping/cracking of the cylinder head.

Milky Oil

When antifreeze finds its way into your car’s combustion chamber, some of it tends to seep away into your engine oil. In turn, when the oil mixes with water over time, it turns milky white. Check your dipstick and the underside of your oil cap for any signs of this mixture. Coolant compromises the lubricating properties of your oil, causing increased wear and tear to the bearings and cylinder walls.

White Exhaust Smoke

If your car has been producing white smoke from the exhaust pipe, then your gasket might be blown.  This case occurs when antifreeze leaks into your car’s combustion chamber. In turn, the blistering heat converts the coolant into steam that flows out of the tailpipe as white smoke. A sweet smell also accompanies the billowing smoke.

External Head Gasket Leak

This is the easiest diagnosis you can make of a blown head gasket. It occurs when the head gasket is faulty between the outer part of the engine and the oil or water passage.  This case can lead to an oil or coolant leak from underneath your exhaust or intake manifold, especially when the car is fully warmed up. Identifying such a leak can be straightforward when no other cooling passages are adjacent to your head gasket. On the contrary, an ultraviolet (UV) dye may come in handy if you find other neighboring cooling hoses. Simply add the dye to the antifreeze/coolant and then use a UV light when checking for a head gasket leak.

Many car users are often asked, “Can you drive with a blown head gasket?” Well, if you notice one or several of the symptoms mentioned above, the best thing is to avoid driving your car until the problem is sorted out. Bear in mind that the cold coolant and hot gases leaking from the gasket can damage the engine block or even cause the metal head to crack or warp.

What Causes a Head Gasket to Blow?

When your head gasket blows, the next cause of action should be identifying the actual cause before considering head gasket repair or replacement. Installing another gasket without fixing the problem will only result in its destruction. With that said, what causes a blown head gasket?

what causes a blown head gasket

Poor Installation

In this case, poor installation may be due to loosehead bolts and failure to set them to the ideal torque. Other mistakes include reusing old/used head bolts, using an inappropriate tightening sequence, failing to clean the block surface, or even utilizing one or several compromised head bolts. These factors, whether individually or combined, pose a risk to the integrity of your head gasket.


This is the number one cause of head gasket damage. An overheating engine exposes extreme temperatures to the gasket. As such, the engine block and head expand at a different rate, forcing the head gasket to crash. Furthermore, the expansion gap created destroys the seal, leading to loss of compression and leaks. Nevertheless, you need to find out why your engine is overheating and fix it before replacing the damaged gasket. Some of the reasons could be a clogged radiator, faulty radiator fan, or leaking coolant, among many others.

Pre-ignition and Detonation Issues

In a normal combustion process, the flame that ignites and burns your car’s air/fuel mixture in the chamber spreads seamlessly and evenly. Nonetheless, low-octane fuel, lean mixture, and overheating can interfere with this process, leading to an abnormal combustion process like pre-ignition or detonation.


This occurs when the ignition inside the cylinder takes place at a slow rate. Such a process allows pressure to build up, which creates a second ignition spot that, collides with the initial combustion process. As a result, the loud knock sound produced from the collision releases internal vibrations that can damage your gasket. Some of the causes of detonation include low-octane fuel, advanced ignition timing, poor distribution of fuel in the cylinder, etc.


On the other hand, pre-ignition occurs before the firing of the spark plugs. This process leads to two combustion spots that collide to produce a pinging sound. Pre-ignition is due to cooling system issues, carbon deposits inside the chamber, overheating exhaust valve, etc.

Hot Spots

Bear in mind that some engines out there are susceptible to hot spots, especially between the cylinder head and central cylinders. However, aftermarket gaskets available for such engines are strengthened to minimize the likelihood of damaging the head gasket. What’s more, replacing your old OEM gasket with the wrong one can lead to a blown head gasket.

How do you Fix a Blown Head Gasket?

In case you notice the mentioned symptoms of a bad head gasket, ignoring them is the last thing you should do. Failing to fix this problem immediately can ultimately damage your exhaust system, fuel injection mechanism, and worst-case scenario, the complete engine. After noticing signs of a failed head gasket, the best thing to do is to stop driving and have the car towed to your nearest mechanic for a proper diagnosis. You can consider the following options as your next cause of action.

blown head gasket test

Using a Gasket Sealant

If you are wondering how to fix a blown head gasket without replacing it, then a gasket sealer is a recommended and cheaper option. Professional-grade sealants are available to help drivers plug gasket leaks. They contain gasket sealing elements that are strengthened using carbon fiber. Most formulas are also antifreeze compatible. As such, you don’t have to pour out your antifreeze to apply the sealer.

Once you have your sealant ready, pour it inside your radiator and top it off with some coolant. The next step is to start rev the engine for about 20 to 30 minutes to allow proper circulation of the sealant before turning off the engine. Once dry, the sealer will form a reliable seal to prevent antifreeze leaks in the engine block and head gasket. Since there are many sealants out there, ensure that you buy your sealer from a credible dealer and brand.

Replacing a Blown Head Gasket

When your car has a massive leak, a head gasket sealer may not effectively do the trick. In such cases, the ideal option is to consult your trusted mechanic on how to go about fitting your engine with a brand-new gasket. Keep in mind that time is of the essence here to avoid additional engine damage. Unfortunately, in this case, you will have to part with a decent sum of money for installation services if you lack the relevant mechanical skills needed.

When replacing your head gasket, get rid of the engine oil and antifreeze by carrying out a radiator flush. This process will help get rid of rust and sediment in the cooling system and allow you to add clean antifreeze once you complete the replacement. Removing the top part will enable you to see the extent of the damage and clean, and prepare the surface for the new gasket. Remember to keep all the small parts you remove in a clean and safe place

How to Prevent Blown Head Gasket?

By now, it’s clear that several factors can lead to a blown head gasket.  If you have experienced this problem, you are aware that it is no ordinary walk in the park. Although the replacement cost of a gasket may not have any significant impact on your finances, the repair work can be quite demanding. The best trick to avoid dealing with a blown head gasket is identifying the common causes of a blown gasket and knowing how to prevent them from occurring.

Don’t wait for your car to start showing signs of trouble, as it could already be too late. Instead, always check for leaks whenever you are working under the hood, for instance, when checking your car’s oil levels. You can take advantage of a good underhood work light for improved visibility. Furthermore, make sure that the coolant level is at the right level and that your thermostat opens correctly before driving off.

As established above, overheating is a leading cause of a blown gasket. It mainly results from various issues, including a faulty radiator hose, a loosely held serpentine belt, a clogged radiator, a faulty EGR system, a spoilt radiator fan, and a damaged radiator cap just to point out a few. To prevent your engine from overheating, ensure that your car’s cooling system is in tip-top condition through proper maintenance. What’s more, you might want to keep a keen eye on your car’s temperature gauge whenever you are driving. Do not ignore any sign of a hot engine.

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Hotspots can also cause damage to your head gasket, especially if your car is old. These spaces can be found between central cylinders and the cylinder head. Modern car manufacturers deal with this problem by reinforcing their engines to keep the head gasket from failing.  Fortunately, if you have an older head gasket, you can replace it with the modern multi-layered replacement gaskets available out there.

Poor installation of your head gasket could lead to all kinds of trouble for your car. If you are a do-it-yourself enthusiast, you better know how to do the job right or rather have some experience.  When installing a head gasket, steer clear of old or damaged bolts as their stability and clamping force may be compromised during the first installation.

If you notice detonation or pre-ignition issues, make sure you consult your mechanic. Additionally, stick to the vehicle manufacturer-recommended oil and coolant.

Final Thoughts

Looking at all the problems posed by a faulty head gasket to your engine and car, it’s safe to say that you need to be quite proactive. Once you spot any of the highlighted symptoms of the blown head gasket, act immediately or risk spending a lot of money on repairs. Always ensure that your coolant levels are okay before going for a long-distance drive to avoid overheating. Additionally, when going for car maintenance, ensure that your mechanic inspects the engine and car thoroughly for any signs of leaks.


Hi there, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanic (Both Heavy Commercial and Private Cars). I worked as a Mechanic and Mechanic Supervisor for over fifteen years at Global Rebound Automotive companies - Toyota, TATA, BMW, Nissan, TVs, and Others. Now, I enjoy my new role of leading a team of automotive experts (in their respective fields) and publish new content on a regular basis on my website and social media.

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