Last Updated on July 5, 2021
With time, aging internal combustion engines become prone to a number of possible failures. While some of these failures are quite minor in scope, others can lead to severe drivability issues, which often necessitate costly repair. This, of course, is never a desirable situation.
Of these more severe issues, few are as despised as a blown head gasket. A blown head gasket is high on the list of troubling issues encountered by motorists, whose engines have begun to show their age. Unfortunately, head gasket repair is seldom simple, or cheap. This fact alone is a common source of concern for those facing such issues.
While blown head gaskets are not extremely common, failures of this type do occur often enough to place increased importance upon recognizing the symptoms of such a condition. By quickly identifying these symptoms, a repair can be promptly initiated, thereby getting your vehicle back on the road in record time.
Read on to learn more about the role of an engine’s head gasket, as well as the various symptoms that accompany a blown head gasket.
What is a Head Gasket?
A head gasket is the specialty seal that lies between an internal engine’s block and cylinder head(s). This seal prevents combustion gasses from escaping an engine’s cylinders, while also preventing the transfer of coolant and oil into an engine’s combustion chambers.
Each engine has 1-2 head gaskets, depending upon the exact arrangement of a particular engine’s cylinders. Inline engines feature only one cylinder head and therefore possess only one head gasket. On the contrary, “V” configuration engines feature two individual cylinder heads and therefore feature a total of two head gaskets.
See Also: V6 vs V8 engine
In the past, copper head gaskets were quite common among production engines, as were various composite gaskets, which typically consisted of graphite or asbestos. Today, most production head gaskets are of a Multi-Layer Steel (MLS) design. These gaskets feature 2-5 layers of thin steel, which are commonly coated in a rubberized coating.
An engine’s head gasket(s) are sandwiched in place between an engine’s block and heads, with the use of precisely torqued head bolts. In many cases, these bolts are of the torque-to-yield variety and stretch when tightened to provide the best possible clamping seal.
An engine’s head bolts are also torqued in a specific manner, which often involves working outward from each head’s centermost bolts.
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
If a blown head gasket allows coolant to enter one or more of an engine’s cylinders, white exhaust smoke is likely to be noticed.
This comes as a byproduct of coolant that is burnt during combustion and downstream travel through a vehicle’s exhaust system.
#2 – Continual Coolant Loss
If your car appears to be losing coolant at a consistent rate, without any visible leaks, there is a good chance that your engine’s head gasket is to blame.
Due to the internal nature of a head gasket leak, coolant is often burnt, without ever being visually expelled.
#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 – Milky Coolant
A head gasket leak often manifests as the swapping of oil and coolant. This often leads to a drastic change in coolant conditions. When this occurs, coolant often takes on a grey or brown coloring and appears milky in state.
Related: Different Types of Coolant
#5 – External Oil/Coolant Leaks
In certain instances, a blown head gasket can cause a visually evident coolant or oil leak. This leak will be present at the mating point between an engine’s block and the cylinder head above.
In rare cases, small bubbles can be observed in leaking fluids of this nature, as small amounts of compression are also purged.
Read Also: Valve Cover Gasket Leak Symptoms
#6 – Engine Overheating
A blown head gasket commonly leads to engine overheating. This occurs for several different reasons, the most common of which relate to coolant loss.
Additionally, the escape of combustion gases into an engine’s cooling system can also play a part in overheating.
#7 – Poor Engine Performance
In instances where compression is lost through a compromised head gasket, an engine’s performance will almost certainly suffer.
This tends to be especially true when a head gasket is blown between two individual cylinders, as compression is allowed to escape through open valves of an adjacent combustion chamber.
What Causes a Head Gasket to Fail?
A head gasket can fail for several different reasons. However, none are as pronounced as overheating. Engine overheating, such as that caused by a significant coolant leak, can lead to the sudden onset of head gasket related issues.
Overheating destroys a head gasket due primarily to the sudden expansion of metal along an engine’s critical surfaces. The more severe an episode of overheating is, the higher the chance of head gasket failure becomes.
Significant expansion of an engine’s cylinder heads or block deck creates a separation between both surfaces, which can ultimately compromise a head gasket’s seal. Even if a single episode of overheating does not cause immediate head gasket failure, the integrity of this seal will forever be weakened.
Detonation, or the sudden ignition of fuel/air outside of the flame front, can also lead to eventual head gasket failure. This stems from the fact that detonation causes damage to a head gasket’s firing rings, which ultimately allows compression seepage.
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.