Located between the cylinder head and the engine block, you’ll find the head gasket. This small yet vital component is used to seal the internal combustion process, allowing coolant and oil to travel throughout the engine to cool and lubricate.
Which means, when it “blows,” it could spell big trouble for the engine. Blown head gasket symptoms are pretty easy to identify and need to be rectified pretty quickly to prevent damage to your engine.
This article will help you understand the head gasket, what it does, and how to know when it fails.
What is a Head Gasket?
In addition to sealing the combustion portion of the engine to allow oil and coolant to circulate, the head gasket also seals the combustion chamber in the engine.
This allows the vehicle to produce enough power to move forward, as well as keep harmful gases from exiting the combustion chamber by directing them through the exhaust system.
The head gasket in modern vehicles is comprised of several layers of steel material entwined with elastomer, making them more durable and longer lasting. Vehicles produced in the past were equipped with gaskets created by graphite or asbestos.
In comparison, today’s gaskets are better as they are less prone to leakage and have little to no health risks as opposed to the produced gaskets.
The head gasket is a vital component within the combustible engine. The head gasket ensures the pressure created from the spark plug’s ignition of fuel vapors remains within the combustion chamber.
The combustion chamber contains the pistons and needs a high amount of pressure to ensure the pistons continue to fire appropriately. Additionally, oil and coolant have equally important jobs but, to perform their tasks efficiently, they cannot mix. The head gasket keeps the chambers separated to ensure there is no cross-contamination of fluids.
What Does it Mean to “Blow” a Head Gasket?
The term “blown head gasket”, is used to describe a head gasket that has been structurally compromised. This compromised segment of a head gasket prevents a proper sealment between an engine’s block deck/cylinder heads. This creates a leak, which can manifest in several different ways.
Depending upon the exact point of failure within a head gasket, several different issues can present themselves. Coolant or oil can be displaced into one or more of an engine’s cylinders, or be purged externally. Additionally, oil and coolant can be displaced into one another, leading to the mixing of fluids.
A leaking head gasket can also allow combustion gases to escape into an engine’s cooling system or into the crankcase itself. Alternatively, a blown head gasket can allow combustion gases of a particular cylinder to escape externally, or into an adjacent cylinder.
Head gasket leaks of any type can lead to a number of drivability-related issues, which can compound as the severity of such a leak progresses. Some of the most serious secondary issues related to a blown head gasket include overheating and compression loss.
Signs of a Blown Head Gasket
A blown head gasket can present many symptoms, which can aid in diagnosis. The prevalence of these symptoms typically varies on a case-by-case basis and is largely dependent upon the exact portion of the head gasket that has been affected.
The following are several of the most common symptoms of head gasket failure.
#1. White-Colored Exhaust Smoke.
Engine coolant is mostly water, and when coolant is burned in the engine, water vapor will come out of the tailpipe as visible white smoke. This is a sign that coolant is being consumed by the engine due to a leaking head gasket.
If coolant isn’t being consumed in the engine, but the coolant level is still chronically low, you may want to look for a leak elsewhere in the cooling system or leaking around the engine on the outside, where the engine block meets the cylinder head.
#2. Continual Coolant Loss.
If the head gasket fails between a coolant channel and one of your engine’s combustion chambers, the engine may start to consume coolant.
This can lead to the engine overheating, too, due to an insufficient coolant level. An engine that’s burning coolant has other symptoms, too…
#3. Bubbling In Cooling System.
A slow, steady bubbling of coolant within a vehicle’s radiator or surge tank is often a sign of ill-directed combustion gases. A specialized combustion gas detector can be used to confirm such a condition with relative ease.
#4. Oil contamination.
One of the clearest signs of head gasket failure is the milky sludge on the underside of the oil filler cap or the dipstick, sometimes jokingly called a “milkshake” or “mayonnaise”. This is caused by coolant getting into the oil, and vice versa.
Although not conclusive proof of head gasket failure this is generally a good indicator and is a sure sign your engine needs to come apart to find the source of contamination.
This also means antifreeze will have contaminated the oil, so any driving will quickly ruin the engine’s bearings.
Repair requires an engine oil flush at the very least, plus a replacement oil filter, and often complete disassembly of the bottom end of the engine to ensure the bearings aren’t damaged and clear out all contaminated oil.
#5. External leaks.
If a cylinder head gasket has blown between the water or oil passage and the outside of the engine, the result can be a simple coolant or oil leak. This is the least dire version of a blown head gasket, but is serious nonetheless.
An external leak may not manifest itself as an immediate problem (other than causing a mess), but if the coolant level is allowed to drop too far, it can lead to serious engine issues. The other issue is that leaking oil could get on the hot exhaust leading to acrid smoke, and possibly fire.
#6. Engine Overheating.
An engine overheating one too many times (as a result of a clogged radiator, coolant leak, faulty fan, etc.) can cause head gasket failure but, conversely, a blown head gasket can also cause the engine to overheat.
Hot exhaust gases can leak into the cooling system, or coolant can leak into the cylinders and be burned off as steam, either way, the end result is an overheating engine.
If the car is driven while overheating, it can also result in the alloy cylinder head warping, or steam damaging the catalytic converter, adding significantly to the cost of repair.
#7. Poor Engine Performance.
If a failed head gasket allows compressed air/fuel to escape, the compression of that cylinder is reduced.
This loss of compression results in a rough running engine and a notable reduction in engine power. This sort of failure typically is accompanied by a sound like an exhaust leak.
What Causes Head Gasket Failure?
Everything undergoes failure after enough time and use, but factors like these can cause head gaskets to fail sooner rather than later:
- Installation Errors: If you’ve recently had your engine rebuilt or replaced, it’s possible that your head gasket was installed incorrectly. Don’t be too hard on the installer, though — head gasket installation can be tricky. Simply over tightening cylinder head bolts can lead to head gasket failure!
- Poor Maintenance: A lack of cooling system maintenance can lead to overheating — the most common cause of head gasket failure.
- Overheating: When your engine overheats, the cylinder head or engine block can warp or expand. When this happens, your head gasket may no longer seal properly.
- Pre-Ignition: Sometimes known as detonation, pre-ignition occurs when air and fuel ignite in the combustion chamber before it is supposed to. When this happens, combustion temperatures and pressures rise. Higher combustion temperatures and pressures can compound overheating and further test the head gasket(s).
Can You Drive with a Blown Head Gasket?
In most cases, a vehicle can be driven with a blown head gasket, though doing so is not recommended.
The seal between an engine’s block and cylinder head(s) is critical to engine performance. Therefore, the degradation of this seal will ultimately lead to a number of drivability-related issues.
In most cases, a leaking head gasket will eventually lead to further overheating issues. Many head gasket leaks lead to coolant loss, whether through external leakage or by way of escape into a specific cylinder.
With time, this loss in coolant will drastically reduce your cooling system’s ability to regulate engine temperatures.
In certain cases, a head gasket leak will allow coolant to mix with an engine’s lube oil. When this occurs, oil dilution is inevitable. This loss in oil viscosity can quickly wreak havoc on an engine’s critical bearings.
As a result, a leaking head gasket can eventually necessitate a complete engine overhaul.
Blown Head Gasket Repair Cost
Head gasket replacement is never cheap. However, the exact cost associated with such repairs can vary substantially from one model of vehicle to the next.
This variance in cost can be attributed to the price difference between particular gaskets, as well as the amount of labor required to replace the head gasket(s) found on a particular engine.
On average, one can expect to pay between $1,200 and $2,000 for complete head gasket replacement. The lower end of this price range is reflective of replacement in an inline-style engine, while the higher end of the price spectrum correlates to most high-end “V” configuration engines.
Preventing Head Gasket Failure
The single biggest way to prevent head gasket leaks involves keeping a close eye on your vehicle’s cooling system.
This involves checking the condition of all coolant and heater core hoses, as well as periodically inspecting your engine’s water pump and thermostat housing seals for fluid loss.
If any issues relating to cooling system integrity are noted, repair should be conducted as soon as possible. Delaying such repairs can lead to an overheating issue at a moment’s notice, which in turn can put your engine at risk for head gasket failure.
Blown Head Gasket vs Cracked Head
Though somewhat rare, an engine’s cylinder head can crack, posing similar symptoms to those associated with head gasket failure. However, a cracked head requires much more than head gasket replacement to remedy.
Since cylinder heads are vital structural components of any engine, such failures require head repair or total replacement. During these repairs, an engine’s head gaskets will also be replaced.
Identifying the difference between a cracked head and a blown head gasket can be quite difficult. Each issue makes it possible for both combustion gases and fluid to end up where they would not otherwise be found.
However, many issues related to a cracked cylinder head will appear to clear up as an engine reaches operating temperature, and the crack itself swells shut.
If any doubt exists as to a cylinder head’s integrity, the head in question should be taken to a machine shop, where further testing can be conducted. As standard procedure, most machine shops “hot tank” suspect heads, in order to visually identify cracks in cylinder heads that would otherwise go unnoticed.