What are the Symptoms of a Blown Head Gasket?

To say that the modern combustion engine is nothing less than a remarkable piece of human ingenuity is an understatement. … Continued

To say that the modern combustion engine is nothing less than a remarkable piece of human ingenuity is an understatement. Being able to produce power that can move several tons of both stationary and moving parts up to a hundred miles an hour is simply a remarkable feat. One very important yet often overlooked component of the engine is the head gasket. This rather thin piece of a component is so critical that its failure can lead to the failure of the engine altogether. So how do you know that you already have a blown head gasket?

The cylinder block of the four-cylinder engine

First Things First

Before we even dig deeper into the issue, it is best to lay down the foundation for our understanding of why a head gasket is so important in a vehicle’s operation. This will set us on the right track especially when we begin identifying and describing some of the more common manifestations of a head gasket that has blown or is starting to fail. So, what is a head gasket?

We all know what a ‘gasket’ is. It’s found in almost every fixture that we have that has a connection whereby we don’t want any of the materials inside to ever escape outside or substances outside ever gaining entry inside. While we don’t necessarily call these materials as gaskets, they do serve the same purpose – to create an airtight, watertight seal so that nothing can escape from the inside or contaminate from the outside. In short, a gasket is a very effective physical barrier to keep the integrity of the inside chamber.

When we apply this to the modern vehicle, we’re looking at the engine which is made up of two principal blocks of metal – the cylinder head and the engine block. The engine block contains cylinders with pistons that move up and down to compress the fuel and air mixture and create combustion. These pistons are mated to rods that are, in turn, connected to the crankshaft. With each up and down motion of the pistons, the crankshaft is spun. The cylinder head is positioned right on top of the block. This contains cylinder valves to allow air and fuel into the combustion chamber and expel exhaust gas from the system.

Connecting these two components are a series of bolts and other secure mechanisms. However, these are often not enough to form a really tight seal. This is why a head gasket has to be compressed in between these two components. This allows the engine to execute its combustion process more efficiently.

Additionally, since a head gasket forms a tight seal between the block and the cylinder head, this component also makes sure that exhaust gases don’t necessarily leak out and that these are channeled through the exhaust. The head gasket also prevents the possible leakage of motor oil and engine coolant into the combustion chamber.

Why It Fails Anyway

Recognizing the symptoms of a cracked head gasket starts with a clear idea of why it fails or why such a piece of technology ‘blows’ in the first place. The answer to this question, you don’t have to look any further than the engine itself.

You’ve got a massive block of metal that operates at very high temperatures. Head gaskets aren’t exactly made of Wakanda’s vibranium or even Logan’s adamantium. Older car models typically come with composite head gaskets such as those made of graphite or asbestos. Newer car models already come with multi-layer steel gaskets that feature elastomeric interleaving. There are also those that use solid copper as material for head gaskets.

Engine overheating is the most common cause of a head gasket leak. Metal expands with the application of heat. If metal is chronically exposed to excessively high temperatures and for unusually prolonged periods, the metal on the head gasket can expand beyond its tolerable limits. This can cause it to break.

Another reason why you may have a failing head gasket is engine detonation or pre-ignition. In a normally-operating engine, combustion occurs only with the application of heat from the spark plug. This also occurs at a very specific point in the stroke of the piston. In pre-ignition, the fuel-air mixture ignites even before the spark plug gets to do its job. The timing is out-of-sync. This puts strain on the head gasket as well as the pistons and valves. Ironically, one of the reasons why there is pre-ignition or engine detonation is because of engine overheating.

Sealing gasket in hand

Knowing You’ve Got a Blown Head Gasket

Since the head gasket is compressed between the block and the cylinder head, it is quite impossible to visually inspect its ‘integrity’ without removing the cylinder head which usually means disassembling the engine. A head gasket may be inexpensive, but it’s the process of removing and disassembling the engine that is often costly. As such, you should learn the different symptoms of a blown head gasket so you will have a better understanding of what you’re up against.

  • Leaking Engine Coolant

There are many symptoms of a leaking engine coolant. However, if you notice the engine coolant to be coming from underneath either the intake manifold or the exhaust manifold and especially only when your car’s engine has already completely warmed up, then a head gasket leak is almost always suspect. This is especially true if you cannot identify other potential sources of the engine coolant leak that is creating a puddle under your vehicle.

If you are not sure whether what you are seeing is a leak from the head gasket or perhaps from other hoses that are part of your engine’s cooling system, then you may want to add UV dye in the engine coolant. You can then use a UV light on the head gaskets to identify potential leaks.

  • Bubbles in the Car’s Radiator

One of the most common signs of a blown head gasket is the presence of air bubbles in your car’s radiator, especially the overflow reservoir container. Since head gaskets prevent the movement of molecules between the inside and outside of the combustion chamber, if there is a leak it is possible that the exhaust gases generated by the combustion process can escape through the leaking head gasket and get mixed into the engine coolant. This pressurized gas is pushed through the engine cooling system and are moved into an area where there’s less resistance. What you will notice is that your radiator or even your engine coolant reservoir will have air bubbles as if you’re boiling water. The funny thing is that this can happen even though it’s cold.

You’d be glad to know that there are now testing kits in the market that can help you identify the presence of leaks in your internal combustion engine. These kits use chemicals to establish the presence of exhaust gases in the cooling system of your car. Professional mechanics say this test is one of the most effective ways to identify a blown head gasket. They are relatively inexpensive and are very easy to perform.

  • White Smoke in Exhaust

We said that the head gasket keeps oil and coolant out of the combustion chamber so that your engine will be performing optimally. Unfortunately, in the event that there is loss in the integrity of the gasket, then there is the possibility that it may no longer prevent the seepage of coolant into the chamber. And since we are talking about a very hot chamber here, the coolant can easily burn or evaporate. The vapors produced mix with the exhaust gases that can be conveyed through the vehicle’s exhaust system. As such, when you do crank your engine, you’d see that highly-noticeable white smoking coming from your car’s tailpipe.

Now, on a cold morning, you might think that this is nothing more than condensation. While it may be true, here’s one way you can be certain that it’s your head gasket that is the culprit. If the exhaust fumes have a rather sweet odor to it, owing to the fact that most engine coolants are made of ethylene glycol, then you definitely have a head gasket issue at hand. Add to this the fact that the white smoke doesn’t really disappear after running your engine for some time. If this is due to condensation, the heat from the exhaust gases should have dried the passages already. But since the white smoke is continuous, you’re looking at a coolant that is leaking into the combustion chamber through a damaged head gasket. This should make you start considering head gasket repair.

  • Engine Overheating

One of the most often overlooked issues in a damaged head gasket is an unusually fast consumption of engine coolant by the cooling system. This is a closed system that should not really get ‘used up’ very fast. The only way this can happen is if there are leaks in the system. And while leaks in the cooling system can be found in other components, you should never discount the possibility of a leaky head gasket.

Since coolant is getting into the combustion chamber and gets ‘burned’ in the process, this uses up most of the engine coolant. This deprives the engine the only way to maintain its optimal operating temperature. Additionally, since hot exhaust gases also get mixed into the coolant, it can no longer provide its engine-cooling effect. When combined with other factors, you can have an overheating engine especially after driving for several hours or tens of miles.

  • Milky or Whitish Motor Oil

One of the symptoms of a cracked head gasket is milky motor or engine oil. This occurs because of the seepage of coolant through the damaged gasket and seeping through the engine’s piston rings. From here, the coolant can reach the motor oil. This can produce a milky white mixture of coolant and oil. When you check your oil dipstick, you will notice this color and consistency in your oil.

The fluid in your car’s cooling system is equal parts coolant and water. The main issue here is the water component. We all know water and oil are hardly the best of friends. This can substantially reduce the lubricant properties of the motor oil which can also expose your camshaft bearings, crankshaft, and cylinder walls to unnecessary wear. If you don’t drive your car, the water in the motor oil can lead to internal engine corrosion. You’re looking at a really costly engine rebuild.

  • Compromised Cooling System

We mentioned above that a car’s cooling system is a closed, pressurized system. This is to help circulate the coolant through the network of hoses, tubes, and passages. Unfortunately, if there is damage to the head gasket in the form of a leak, then the pressure will not be maintained. This can cause low pressure, preventing the coolant to be efficiently circulated throughout the system.

However, it is important to recognize that a low-pressure cooling system is not exclusively caused by a blown head gasket. It can be due to other causes as well. This can also be brought about by a damaged or even a missing radiator cap or coolant reservoir or even leaks in the radiator hoses.

  • Deposits in the Spark Plug

They call this ‘fouling of the spark plug’ primarily since the spark plug gets exposed to engine coolant leaking through the failing head gasket. While the coolant doesn’t get in touch with the spark plug, it can produce particles that can stick onto the electrode and ground strap of the spark plug. This occurs because the coolant is ‘burned’ during combustion, leaving behind microscopic particles.

Close-up of the cylinder block

However, just like low pressure cooling system, having deposits in the spark plug doesn’t necessarily mean it is 100% a head gasket issue. It can be because of engine overheating, very lean air-fuel mixture, loose spark plug, incorrect heat range of the spark plug, or even incorrect ignition timing. What we’re saying is that you should always look at other potential causes of such a problem than quickly blaming it on your head gasket.


  1. 5 Signs of a Blown Head Gasket – Do It Yourself
  2. Head gasket – Wikipedia