Blown Head Gasket: Most Common Causes And Symptoms

Are you having some weird issues with the engine in your car that may seem like a blown head gasket related problem? If it’s the case, it’s very likely that you’ll first Google it or talk to other car enthusiasts. If so, you’ll probably learn that there are several telltale signs of a blown or cracked head gasket. Some will claim that an overheating engine, mysterious coolant loss, and white exhaust smoke are positive indicators of this dreaded failure. Others link it with a white, greasy substance on the oil filler cap, dipstick, and inside the coolant expansion tank. While none of these claims are wrong, in most cases they will only reveal part of the problem. In this article, you will learn everything you need to know about the most common symptoms, potential causes, and estimated repair costs of a blown head gasket.

What are the symptoms of a blown head gasket?

As you may have seen in our previous article, the head gasket is a complex component performing several important tasks. One of them is to seal engine cylinders and stop combustion gases from escaping. If it breaks or starts leaking, pressurized gases inside the cylinders will be able to enter your car’s cooling system. This will cause air bubbles in the system which will, in turn, create overheating problems and even cause the coolant to escape out through the radiator cap. A blown head gasket can also allow coolant to drip into the cylinder which will create large amounts of white smoke coming out of the exhaust. However, many of these symptoms can also be related to cooling system issues, like a broken pump or clogged radiator.

Overheating car because of a head gasket

A white-colored greasy substance can also result from head gasket cracks and subsequent leaks between the oil and coolant passages. When oil comes in contact with coolant or water, it forms an emulsion that looks like mayonnaise or peanut butter. If you notice this inside the expansion tank, the radiator and the engine, your head gasket is probably blown. Still, having this inside the engine may also result from a condensation that happens during frequent short drives. To rule it out, take your car for a longer drive, as this will evaporate any traces of water vapor. Once the car has cooled down, removed the radiator cap and look into the radiator for brown bubbles floating in the coolant.

Besides these usual failure points, there is also one component that can have similar symptoms and throw you off-course. Most modern engines have an engine and transmission oil cooler, whose job is to keep the oil temperature within a certain range. In it, oil goes through a series of water-cooled channels. If any of them cracks, the oil will mix with the coolant and form a white emulsion that will appear within the coolant tank. However, the biggest difference between this and a blown head gasket is that there will be no emulsion inside the engine or the transmission.

Can you drive with a faulty head gasket?

Having determined that the head gasket is blown, you could wonder if it’s possible to drive your car before fixing it. Sometimes, the engine may seem to run fine, tempting you to use it for shorter trips. However, even the smallest leak can have severe consequences on your engine.

The overheating on its own can cause additional damage to your engine, even if you drive it on short distances. Driving a car while it’s overheating might crack the cylinder head(s). In the worst-case scenario, it could cause the pistons to seize, bend the connecting rods and damaged cylinders beyond repair. Besides this, leaking head gaskets lead to higher-than-normal pressure inside the cooling system, resulting in cracked radiators or blown radiator hoses. To make things worse, coolant that gets burned inside the cylinders can cause irreversible damage to catalytic converters and oxygen sensors.

If the blown head gasket allows oil and coolant to mix, the resulting emulsion will also cause several problems. When it happens, the oil in your engine will lose its lubricating properties. This can cause expensive damage to moving and rotating parts inside the engine, such as bearings or valve train components. As the oil gets inside the cooling system, it can lower its efficiency and lead to overheating under heavy load. In the end, greasy emulsion that creates deposits in all cooling system components can be hard to flush out. Because of it, you could have issues with your car even after repairing the head gasket. Such faults could include clogged radiators, obstructed heater cores, and cracked hoses.

What are the causes of a blown head gasket?

Although not the only one, overheating is the most common situation causing a head gasket to blow. When the engine reaches temperatures outside of the normal operating range, sealing materials within the head gasket become brittle. Combined with high mechanical forces that happen because of thermal expansion, this often causes head gaskets to start leaking.

Auto mechanic replacing a blown head gasket

Besides overheating, blown head gaskets can also happen because of hot-spots, where local temperatures are higher than normal. One of the causes of hot-spots is carbon deposits in the engine head causing pre-ignition. This means that the air-fuel mixture ignites before the spark plug triggers it.

How much does a head gasket replacement cost?

Although most people associate it with hefty repair bills, you may find that the head gasket doesn’t cost that much. However, the amount of work that goes into replacing a head gasket can multiply that price several times. As the head gasket is one of the engine’s core components, you need to disassemble most of your engine to replace it. This calls for either replacement or refurbishment of most components you have removed during this process, which also impacts the price.

Auto mechanic machining an engine head

Furthermore, before reinstalling a new head gasket, you need to take your cylinder head to a specialist shop qualified in engine machining. These shops can examine your head for any damages and prepare it for installation. This is an essential step, without which the new head gasket would not seal properly. Besides machining the cylinder head, you’ll need to replace head bolts, various gaskets, and timing belt assembly.


If your engine suffers from overheating or pre-ignition, it may blow its head gasket with time. Some symptoms that may indicate head gasket problems include overheating, coolant loss and brownish emulsion within the engine and cooling system. However, determining if the head gasket is blown can be tricky, as other failures can create similar symptoms. Make sure to rule out all other possibilities before venturing into head gasket replacement, as this is an expensive repair. As always, when in doubt, make sure to get help from a trustworthy auto mechanic. Doing so will ensure you don’t throw your hard-earned money out of the windows.

About Bojan P

My name is Bojan - I am a car enthusiast, specialised in the vehicle diagnosis, repair and maintenance with 10 years of practical, hands-on experience. In addition, I have a Masters degree in mechanical engineering.

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