In an internal combustion engine, the head gasket acts as a seal between the engine block and the cylinder head(s). Its primary role is to contain the combustion gases within the cylinders while preventing coolant or engine oil from leaking into them.
A damaged head gasket can lead to engine overheating or poor performance. Well, in this reading, we’ll explore what a head gasket is, how it functions, its location, the diagram, and how it works. We’ll also explore the symptoms of a blown head gasket, how to test and replacement costs.
Let’s begin!
What is Head Gasket?
The head gasket is made of a very thin metal sheet with perforations of various sizes. They serve to form a seal between your Subaru’s cylinder heads and engine block. The pressure from the combustion chamber is contained by a strong seal while it is doing its job.
In order to prevent a mix-up, the gaskets help keep the coolant where it belongs and the oil flowing through the oil passageways. Head gaskets should only need to be replaced with significant repairs because they are designed to last as long as your engine.
The head gasket, positioned between the cylinder head and the engine block, plays a crucial role in sealing the internal combustion process. It allows coolant and oil to circulate throughout the engine for cooling and lubrication.
However, if the gasket “blows,” it can lead to significant engine issues. Symptoms of a blown head gasket are typically easy to spot and should be addressed promptly to avoid severe engine damage.
Functions
The head gasket in an internal combustion engine serves multiple critical functions. It seals the combustion chamber, allowing oil and coolant to circulate without mixing while ensuring the engine generates enough power to propel the vehicle.
By directing harmful gases through the exhaust system, it also prevents their escape from the combustion chamber.
Modern head gaskets are made of several layers of steel combined with elastomer, offering enhanced durability and longevity. In contrast, older vehicles used gaskets made from materials like graphite or asbestos, which were more prone to leakage and posed health risks.
As a vital engine component, the head gasket maintains the pressure created by the spark plug’s ignition of fuel vapors within the combustion chamber, which houses the pistons. This high-pressure environment is essential for proper piston function.
Additionally, the head gasket prevents the mixing of oil and coolant, ensuring these fluids perform their respective tasks effectively without cross-contamination.
Related: What is an Intake Manifold Gasket? – its Functions and How it Works
Diagram
Symptoms of a Blown Head Gasket
The common signs of a blown head gasket are listed below:
- Engine Overheating
- Milky Build-Up Under Oil Cap
- Visible Tailpipe Smoke
- Rough Idle
Engine Overheating
When the engine overheats, you’ll be left wondering which issue came around first. Did the engine overheat as a result of the head gasket leaking into it, or did the hot engine cause the parts to bulge, which then allowed the head gasket to leak?
Regardless of what causes the issue, running a car with an overheated engine is a surefire way to end up with an engine failure.
Milky Build-Up Under Oil Cap
It is simple to determine whether the head gasket on your engine has blown. Simply look under the oil filler cap. The interior of the oil cap should be basically dry if the gasket is good.
You probably have a gasket leak if you find a milky, brownish-yellow fluid that resembles the consistency of a milkshake. The milky substance is engine oil contaminated by coolant and oil that has leaked past the head gasket.
After becoming polluted, your engine oil is no longer able to adequately protect it. Get a head gasket replacement as soon as you can if you think this may have happened.
Visible Tailpipe Smoke
The head gasket controls how coolant moves through the engine’s coolant channels. Coolant may seep into the combustion changers, which are close to the coolant channels, if the head gasket fails.
The liquid will burn alongside gasoline. This causes the tailpipe to continuously emit white or gray smoke. This is a blatant indication that your head gasket is faulty.
Rough Idle
Between two combustion changers, the head gasket can also degrade. A high pressure level must remain inside the cylinders of the engine at all times.
The engine will run badly and have a choppy idle when the head gasket fails since it won’t be able to maintain the proper level of pressure. A rough idle should not be ignored even though it is not a certain sign of a faulty gasket head.
What Happens If a Head Gasket Blots?
When the seal breaks, combustion pressures, and exhaust gasses are let into the cooling system. To prevent boiling, the cooling system is designed to maintain pressure. The cooling system is unable to function when there is a head gasket leak, and the uncontrolled heat can do serious damage to your car.
Other Ways to Tell If you have a Defective Head Gasket?
- White exhaust smoke, which is caused by antifreeze leakage into the cylinders that turn into steam.
Power loss because the engine can’t handle high combustion pressures. - A burning odor.
- Overheating: hot gases could enter the cooling system or coolant could start to leak.
- Bubbling exhaust.
- Coolant leaks into the oil, giving it a milky appearance; if you drive with this, serious damage could result.
External leaks: The engine may have coolant or oil leaks.
Related: Engine Overheating: Causes, Symptoms, and Solution
How to Test a Blown Head Gasket
When diagnosing a blown head gasket, follow these steps:
Examine Your Engine Oil
Examining your engine oil is a straightforward and dependable method to identify a blown head gasket. You can check it by lifting the dipstick, but draining the oil from the pan and looking is much more effective if you’re on the point of needing an oil change.
It’s a sign of a blown head gasket when engine oil and coolant mix. If your oil has a milky hue rather than the dark brown or black of old oil, it is mixed. The color will be milkier the more coolant is present.
Since your coolant is a sealed system, everything you put in it should stay there. And even though the levels may occasionally change somewhat due to variations in pressure and temperature, however, they should basically be constant.
There is an increased chance that your coolant is leaking within your engine if you find that you need to continually add coolant to the system despite the lack of a visible leak.
If there is too much smoke, it enters the combustion chamber, and if there is milky-colored oil, it enters the oil channels.
Additionally, if there is oil in the coolant reservoir, you’ll notice a foamy or milky appearance that indicates a problem, just like your oil can change color if it’s mixing with the coolant.
When the coolant cap is removed and smoke is seen coming from the coolant reservoir, compression may also be taking place within the coolant system. An exhaust tester can also be used to test this.
Check Your Spark Plugs
Coolant or oil on your spark plugs is a reliable indicator of a blown head gasket. Even while this isn’t as simple to find as checking your oil or exhaust, it’s a surefire approach to identifying the issue.
Simply remove your spark plugs and give each one a thorough inspection. You have an issue and it’s probably a blown head gasket if you see any oil or coolant residue on the spark plug’s tip.
Check Your Exhaust
If you see much more smoke coming from your exhaust than usual, you may have a blown head gasket. When diagnosing excess exhaust, there are a few factors you should be aware of.
First, expect more emissions than in warmer weather as the outside temperature decreases. This is completely typical and excludes blown head gaskets.
Second, if you have a blown head gasket, you should be on the lookout for excessive white smoke since coolant burns this color when it enters the combustion chamber.
Finally, for the issue to be a blown head gasket, there must always be an excessive amount of smoke. The issue is probably not a blown head gasket if the amount of exhaust smoke varies after warming up or on different days.
Check For Leaks
Fewer people are aware that blown head gaskets can cause external leaks, despite the fact that most people are aware that they can cause fluid to move to other areas of your engine.
It all depends on where the leak is. Fluid will drip down the outside of your engine rather than enter various channels if it is closer to the outside of the head gasket.
If it pools up and burns off before it reaches the ground, your engine may emit smoke as a result. Or, if it does fall to the ground, the fluid should start to pool up underneath your car.
The only method to determine if this fluid is coolant or oil is to follow the leak’s path back to its origin. You’ve identified the issue if you do discover that the head gasket is the source.
Inspect the Radiator
When inspecting your radiator, there are a few distinct things you can look for. A blown head gasket will first allow air into the cooling system, which will result in a frothy or foamy mixture in the radiator.
Additionally, the system might contain a mixture of fuel and oil. If that occurs, when you examine the radiator, the mixture will have a milky tint.
Run a Compression Test
This test is one of the trickiest to execute, but it’s also one of the best. To accomplish this, you’ll need a few specialized tools, and you’ll also need to remove the spark plugs.
Make sure to inspect the spark plugs for any coolant or oil residue before you remove them. If you have a blown head gasket, you’ll notice a decrease in compression in the afflicted combustion chamber.
This is due to the fact that the cylinder can never entirely seal, and the extra pressure will always escape. However, this strategy might make it exceedingly difficult to detect small breaches.
What Subaru Models Are Affected by Head Gasket Issues?
The composite-style head gaskets used in the Subaru EJ251, EJ252, and EJ253 engines make them the most prone to head gasket issues.
These 2.5-liter engines were available in a variety of setups and saw a few production-related updates. Any engine could experience a head gasket failure, but some Subaru models are particularly prone to it.
It turns out that the engines’ design contributed to the head gasket issues. The following Subaru models appear to be the most susceptible to head gasket issues: 1999–2010 Forester, 1999–2011 Impreza, 2000–2009 Outback, 2000–2009 Legacy, and 2003–2005 Baja.
Naturally, the design of the boxer engine may also be at fault.
The engine of a Subaru boxer motor is flat, as opposed to standing up like those in most other models. The pistons in these engines oscillate side to side.
The engines have fantastic weight and balance characteristics, but when the engine is shut off, fluids pool up adjacent to the head gasket rather than draining normally. The fluids’ acids begin to eat away at the seal even after the pieces are improved.
Replacement Cost of a Blown Head Gasket
The average cost of replacing a head gasket is between $1,000 and $2,500, often even more. The price of a head gasket replacement might vary significantly based on the make and model of the car, where you reside, which auto repair shop you choose, and other factors.
This price includes the labor involved in disassembling the engine, swapping out the gasket and other required components, and putting it back together. If necessary, it might also cover the price of resurfacing the engine head.
It’s crucial to remember that replacing a head gasket is a serious repair that calls for a high level of competence; as such, a novice shouldn’t attempt it. Bring your car to a reputable, skilled mechanic who can handle the repair correctly and securely.
The cost to replace a Subaru head gasket will often range from $2,000 to $4,000. Sadly, the cost of just the labor alone can range from $1,200 to $3,000.
A typical parts bill should be expected to be between $800 and $1,500, especially once the tensioners, idlers, water pump, timing belt, and seals are taken into account. Additionally, you might have to pay up to $500 more overall if your Subaru has a manual transmission.
How Can a Head Gasket Be Replaced?
It takes a great deal of effort and knowledge to replace a head gasket. The good news is that you shouldn’t have any repeat failures if you have the work done by a Subaru expert.
The engine is entirely removed from the car before being disassembled and checked for internal component damage. Any problems are identified, diagnosed, and reported.
To ensure that the heads reseal properly, the motor is then cleaned and prepared. The engine is disassembled again, examined, and then put back into the car.
FAQs
What can be mistaken for a blown head gasket?
Many vehicles frequently experience coolant and oil leaks. You don’t necessarily have a blown head gasket just because you notice a leak. However, if you see that most of the oil or coolant is leaking from the engine block, it can be a sign that the head gasket is no longer keeping a seal.
What is the best test for head gaskets?
Checking for the presence of combustion gases in the engine coolant is the most efficient and accurate diagnostic technique to establish whether the cylinder head gasket is sealing combustion gases. When performing this, the radiator cap must be off and the engine must be heated.
How do I know if my head gasket is cracked or blocked?
When you can see that the engine’s antifreeze has become mixed with the oil, that is a big symptom of a broken engine block or burst head gasket. The circulating engine antifreeze may contaminate the flowing engine oil if there is a fractured block or blown head gasket.
How do you check for a blown head gasket with a pressure tester?
You can see if the pressure in the system remains constant or drops over the course of a few hours once the air source has been cut off. Pressure loss over time is a sign of a leak, so check for it immediately. The likelihood of having a head gasket leak increases if the leak cannot be located externally.
How does a blown head gasket sound?
Depending on how the head gasket bursts, you can even hear a knocking noise coming from the engine or the sound of a misfire. An overheated engine, a coolant leak, or decreased compression as a result of harsh idling are all possible causes of the sound of a misfire.
How do you fix a blown head gasket without replacing it?
- Flush the cooling system after removing the thermostat.
- Add water to the system.
- As the car idles, slowly add BlueDevil Head Gasket Sealer to the radiator.
- Place the radiator cap on and give the engine a minimum of 50 minutes to idle.
Can you seal a blown head gasket?
In a nutshell, yes. However, head gasket sealers are not a long-term cure for a blown head gasket. These products only work temporarily and have a limited shelf life; eventually, wear and tear will need to be repaired for your car to function properly once more.
Can a car run normally with a blown head gasket?
Yes, in short, but it is not advised. Ignoring a blown head gasket will probably result in more harm to your engine and your finances. The most crucial and essential components of any engine that serve to seal off compartments are gaskets.
Can a car still run with a blown head gasket?
Driving with a burst head gasket will surely result in other car problems. Before it’s too late, K-Seal can stop the issue in its tracks. Technically, driving with a blown head gasket is possible, but we never recommend it.
What does exhaust look like with a blown head gasket?
If you see white smoke coming from your exhaust, there is probably coolant leaking into the cylinders. The head gasket breach that causes the coolant to produce this white steam most frequently causes this to occur. Have it fixed so that the breach doesn’t continue to grow.
How long does a blown head gasket last?
The short answer is that they ought to last as long as your engine. However, the likelihood is that you will need to replace the head gasket in your car at some point throughout its lifetime if you don’t properly maintain it or the engine.
Does Subarus have head gasket problems?
Many Subarus have a high failure rate for the head gaskets. Under ideal circumstances, they should last 100,000 miles. The mileage of your car will vary based on a number of variables when the gaskets fail. What year and type of Subaru do you own?
How much does a Subaru head gasket cost?
For a Subaru, the starting price for a head gasket replacement is about $3,000.
Can I drive Subaru with a leaking head gasket?
The quick answer is yes, but it is not advised. Ignoring a blown head gasket will probably result in further harm to your engine and your finances. The most crucial and essential components of any engine that serve to seal off compartments are gaskets.
What can be mistaken for a blown head gasket?
The most typical misdiagnosed signs of a ruptured head gasket are coolant mysteriously evaporating or an engine overheating for no discernible reason. It becomes immediately clear that these two things combined actually make a lot of sense if you have a solid understanding of the cooling system in your car.
Can a car run normally with a blown head gasket?
why driving after having a blown head gasket is not advised. Because a head gasket serves as a seal, your engine will lose pressure right away if it blows. You will experience a considerable loss of power as a result of the combustion chamber’s pistons no longer firing forcefully due to the pressure reduction.
How does a blown head gasket sound?
The compression of that cylinder is decreased if the head gasket leaks, allowing the compressed air and fuel to escape. This decrease in compression causes the engine to function poorly and significantly reduces engine output. Typically, this kind of failure is followed by an exhaust leak-like sound.
What causes head gasket failure?
The most common cause of head gasket failures is engine overheating, therefore make sure the coolant level is maintained and that the cooling system is functioning properly with no leaks and an effective radiator. Future harm can be avoided with a head gasket that is placed correctly.
