Customer 
When a vehicle owner hears “you have a blown head gasket,” it creates fear. It is a bad diagnosis that makes one think of big-dollar repairs and cars blowing smoke. But what exactly is a blown or cracked head gasket? Why does it happen? And most importantly, can it be repaired?
In this all-inclusive guide, we will cover everything you need to know about this serious engine failure, allowing you to be able to identify the signs of a blown head gasket, control the cost of your repairs, and possibly avoid the need to repair it altogether.
To know what a “blown” head gasket (more properly, a “cracked” head gasket) is, you need to understand what it does.
Your engine consists of two major sections:
The head gasket is located between the two heavy pieces of metal and serves to provide an adequate seal, preventing combustion gases, oil, and coolant from mixing or leaking between them. It is arguably the most highly loaded of all your engine seals.
The cylinder head gasket is subjected to high pressure (up to 1000 psi) during combustion, and the temperatures vary widely throughout operation. The cylinder head gasket separates the water jackets (cooling system) with oil galleries and keeps all combustion gases inside the cylinders.
The terms blown head gasket and cracked head gasket often get confused. Gaskets do not really crack; they typically “blow” or fail.
Both of these scenarios could result in the same symptoms for the owner of the vehicle, and they both will require intensive repairs that are similarly complicated.
Due to the positions of their location, when a head gasket fails, the resulting symptoms can be very severe and impossible to ignore. Here are three common examples of head gasket failure:
Persistent Engine Overheating: If your engine constantly keeps overheating even though the coolant level has been checked. This is most likely due to combustion gases leaking into your engine’s cooling system and causing a severe and almost impossible-to-repair overheating condition.
Thick White Smoke From The Exhaust: If you see a large volume of thick, sweet-smelling white smoke (unburned fuel) being produced by your vehicle’s exhaust system, this would indicate that engine coolant is leaking into the combustion chamber and burning fuel.
Milky, “Milkshake” Oil: If you look at the dipstick in your engine or look under the cap of your oil filler, you will see an oily substance that has a light brown color (milk coloured). The presence of this substance indicates that the engine coolant is leaking into the engine oil, which in itself is a potentially serious problem.
Bubbles in the Radiator or Overflow Tank: A leaking combustion gas into coolant passages creates air-pumping action that creates bubbles that make a bubbling noise (or what is often referred to as “champagne-like” bubbles) from your Radiator.
Unexplained Coolant Loss: If you continually have to add coolant but there are no visible leaks (pools of water/oil) below your car, the coolant is being used up during combustion within the engine.
Rough Idle and Misfires: Coolant leak problems from a blown head gasket, which can also lead to loss of cylinder compression, can cause the engine to experience an excessive amount of fuel (from both the leakage from the cylinder head gasket), and thereby result in rough idle and misfire.
External Leaks: At times, due to an externally damaged head gasket, coolant can flow from above (i.e., outside) to below (i.e., inside). This can happen when coolant overflows from the overheating radiator, or when coolant leaks from the head (if the head is installed improperly).
While head gaskets should be able to last the entirety of an engine’s life, they will often last a much shorter duration than intended. Most head gasket failures are the result of excessive engine temperatures.
The excessive temperatures that cause head gasket failures are a result of 4 different issues:
Overheating – Your car’s head gasket can be damaged if your vehicle loses coolant due to broken hoses, water pumps, or frozen thermostats, due to the heat-up process caused when the engine overheats. Because the aluminum head expands faster than the cast iron block, we experience a shearing force (crushing action) that damages the head gasket.
Pre-Ignition / Knock (engine knock) – the engine will have high combustion pressure from a faulty ignition timing or low-octane fuel. The high combustion pressure destroys the “fire rings” (metal rings around the cylinder holes).
Improper Installation – on previous head replacements or unsuccessful substitutions, if the bolts were not properly secured and in proper sequence, an improper installation results in leaking.
Age/Wear – on high mileage vehicles, the continuing stress of thousands of heat cycles (heating and cooling of the engine), causes the material of the head gasket to fail.
No. If you think your head gasket is blown, you should stop driving right away. If you continue to drive with a blown gasket, it will turn a repairable head gasket into an engine with a cracked block or a seized engine (destroyed).
The following will likely occur if you drive with a blown gasket:
The job of replacing a head gasket consists mainly of labor. A head gasket can cost from around $100-$300. Most of the cost of this procedure will come from the labor required to take the engine apart.
In cases of severe overheating, the cylinder head may need to be milled flat or replaced if it has cracks, creating additional costs.
As a skilled mechanic, you may have the ability to perform a head gasket replacement by completing a detailed and multi-day, step-by-step process; however, for many others, having a professional complete this work is their only option.
What about Sealant Products?
Minor leaks require the temporary sealing of a radiator or the use of chemical-based radiator sealants to repair them.
With good maintenance, it’s possible to prevent a head gasket from failing.
A cracked head gasket can be one of the most stressful repairs for a vehicle owner and has two of the highest stakes of any repair: cost and how important the repair is to the continued usability of your car, but it doesn’t have to equal the end of your car’s life.
Whether you have noticed the sweet smell of coolant or that your temperature gauge is climbing, waiting to see what happens to your car can quickly become your engine’s worst nightmare!
So treat your cooling system with respect, watch your gauges, and fix those small leaks before they become the “big one”. Both your car and your wallet will thank you later.
The best way to keep costs down is by catching any symptoms as early as possible; so if you see white smoke, a “milkshake” on your dipstick, or your engine is getting very hot, don’t ignore it.
If you act quickly enough, there is a good chance you will save your engine and avoid replacing your vehicle.