Is your head gasket leaking oil? Sorry to be the bearer of bad news but a blown head gasket is going to be very expensive to repair. But the good news is, if you’re seeing oil leaking externally, that might not be a head gasket problem.
Instead, it might be a valve cover gasket problem. While equally important, it’s a lot less expensive than replacing a head gasket. In this post about head gasket leaking oil, we’ll explain everything you need to know:
- What’s A Head Gasket?
- Blown Head Gasket Symptoms
- Bad Valve Cover Gasket Symptoms
- Repair & Replacement Costs
- DIY Fixes & Repairs
- Final Conclusion
In the simplest terms, the head gasket is a seal that connects your engine block to the cylinder head. Its main purpose is to prevent oil and coolant from leaking into the cylinders. Additionally, it prevents combustion gases from escaping, thus ensuring optimum compression inside the engine. It also acts as a sort of cushion for the block and the cylinder head.
Like many other car parts, the gasket will wear down over time and won’t seal properly. For your information, a failed head gasket is often referred to as a “blown head gasket.” This can lead to several problems, including oil leaking out of its designated passageways.
However, when the head gasket blows, it usually leaks oil into the engine cylinders or mixes it with the coolant. Head gasket leaks rarely leak oil to the outside of the engine, although this can happen.
Instead, an external oil leak typically means you have a bad valve cover gasket. What’s a valve cover gasket, you ask? Good question, the answer is right below:
Valve Cover Gasket
The valve cover is, well, a cover for the engine valves. In older engines, that’s part of the engine you will see when you open the hood. In most modern cars, you’ll have to take off the plastic cover before you can see the valve cover.
A bit more explanation: your car has a series of valves, which is the device that controls the passageway for fuel to enter cylinders and for exhaust gases to escape. As with any moving part, the valve is lubricated. The cover is there to keep the oil inside and prevent contamination.
The gasket sits between the valve cover and the cylinder head. And much like the head gasket, it’s there to prevent oil from seeping out. The valve cover gasket is usually made from cork, plastic, or sometimes metal. Over time, the gasket can fail.
When it comes to a head gasket failure, oil can either leak out or into the engine. Meanwhile, a valve cover gasket failure can only leak oil outside of the engine.
So, if you see oil leaking externally, it can either be a head gasket or a valve cover gasket failure. But how can you tell them apart?
Blown Head Gasket Symptoms
Let’s take a look at the symptoms of a bad head gasket first. The symptoms are usually more obvious and easier to spot:
Head Gasket Leaking Oil, Symptoms #1. Oil Leaking Down The Engine
As mentioned, a blown head gasket rarely leaks oil to the outside of the engine. However, this can still happen, and if you see oil on the middle to lower parts of your engine, this is likely a head gasket problem.
That’s not to say that a valve cover leak can’t cause this as oil can drip down the engine. However, you’ll likely see that the top part of the engine is covered in oil as well, as that’s where the valve cover is located.
Meanwhile, if the leak is only coming from the bottom of your engine, that’s an entirely different problem. That means there’s a leak coming from the oil pan. Either the pan is damaged, or its gasket has worn out. Read our article about oil pan replacement to learn more.
To verify whether or not you have a head gasket leak, see if you’re experiencing these other symptoms as well:
Head Gasket Leaking Oil, Symptoms #2. Blue Or White Smoke From The Exhaust Pipe
One of the most common symptoms of a bad head gasket is when your exhaust pipes produce smoke that’s either blue or white in color.
As mentioned, it’s more common for a blown head gasket to leak oil into the engine rather than outside of it. When oil leaks into the cylinders, the engine will burn it along with the fuel and air mixture. This results in a blue smoke coming out of your exhaust (as well as blue smoke from exhaust on startup).
Meanwhile, a thick white smoke means there’s excess moisture inside the cylinders. Water and moisture can enter the engine during cold weather. That’s why you might see white smoke coming out of your tailpipes on a cold start during those really cold mornings, which is quite normal.
However, if the smoke is very thick and persists even after the engine warms up, this means coolant is leaking into the cylinders and is being burnt with the fuel and air mixture. Courtesy of a blown head gasket, of course.
The smoke can either be blue or white. It depends on which part of the head gasket is leaking which determines which fluid is entering the engine’s cylinders. Either way, a gas engine is supposed to produce clear and almost odorless smoke.
As a final note, your car may produce black smoke as well. While quite normal in a diesel engine (especially older ones), if this happens with a gas engine this means your engine is using too much fuel.
There’s a myriad of potential causes, but it’s not head gasket-related. A clogged air filter, bad fuel injectors, or a faulty Mass Air Flow (MAF) sensor may cause this. The worst-case scenario is that you have damaged piston rings.
Head Gasket Leaking Oil, Symptoms #3. Oil And Coolant Mixing
The head gasket can break and leak in different ways. It can leak in such a way that it will allow the two fluids to mix, without leaking them into the cylinders or the outside of the engine.
So, how to check if your oil and coolant are mixing? First, check the engine oil dipstick. It’s fairly straightforward:
- Locate the engine oil dipstick. It usually has a yellow handle that says ‘Engine’ or ‘Oil’ on it.
- Take the dipstick out, and inspect the fluid.
- Oil on the dipstick is supposed to be either clear or really dark and thick (in this case your oil is a bit old). However, if the oil is light brown and looks like gravy, this means coolant is mixed with the oil.
Checking for oil in the coolant is also straightforward:
- Allow for the engine to cool for at least 15 minutes if you’ve been driving it. You do not want to open the radiator cap while it’s still hot.
- Open the radiator cap, and inspect the coolant inside it.
- If there are brown and black specks in the coolant, then the two fluids are mixing. The two fluids don’t mix together, so it’ll be fairly easy to spot the specks.
Regardless of how the gasket leaks, you don’t want the two fluids to mix together. Coolant mixing with the oil can reduce its ability to lubricate the engine, which can lead to overheating and excess wear on the engine.
Meanwhile, oil mixing with the coolant will reduce the coolant’s ability to carry heat away from the engine. Needless to say, this can cause your engine to overheat and damage it in the long run.
Head Gasket Leaking Oil, Symptoms #4. Bubbles In The Radiator
Bubbles in the radiator mean that the head gasket leak is allowing combustion gases to escape and enter the cooling system. The leak may be causing this rather than mixing the oil and coolant. Here’s how to check:
- Wait for the engine to cool down if you’ve been driving. Again, you don’t want to open a hot radiator cap.
- Once cool, open the radiator cap.
- Turn on your engine and inspect the coolant inside the radiator. Make sure not to touch anything and keep a safe distance.
- A bit of bubble is normal, it usually means there’s a bit of trapped air in the system. But if it persists after 5 – 10 minutes of idling, then there’s a leak in the cooling system.
- Turn off the engine and reinstall the radiator cap.
The most common cause is a blown head gasket that’s allowing combustion gases to enter the system. However, a faulty radiator pressure cap or damage to the cooling system.
In any case, bubbles in the coolant are bad since they can reduce the system’s efficiency in keeping your engine cool. Cross-check with other symptoms to see if it’s a head gasket problem. If no other symptoms exist, then it may be a cooling system problem.
Head Gasket Leaking Oil, Symptoms #5. Low Oil Or Coolant Level
Since a head gasket can cause oil and/or coolant to leak, their levels will decrease as well. A low oil level is a bit harder to notice, and you’ll have to check it via the engine oil dipstick. Here’s how to check:
- Turn off the engine, and locate the engine oil dipstick.
- Take it out, wipe the stick clean, and then fully reinsert it back into the slot.
- Take out the dipstick, and inspect it. There are markers to indicate the minimum and maximum oil levels.
Meanwhile, a low coolant level is often more noticeable since it will result in an overheating engine. If your temperature gauge is higher than usual, check your coolant reservoir and see if it’s at the minimum marker.
In both cases, there might be other reasons why your engine is losing oil or coolant. You may have an oil pan leak that causes rapid oil loss. Meanwhile, your coolant level may be low because of a cooling system leak.
However, if you can’t seem to locate a leak, this often means you have a head gasket leak that’s causing these fluids to burn off with the engine. Unexplainable oil and coolant loss almost always means you have a faulty head gasket.
Head Gasket Leaking Oil, Symptoms #6. Compression Loss And Engine Misfires
As mentioned, the head gasket helps to prevent combustion gases from escaping thus ensuring optimum compression. When one or more of the cylinders loses compression, it will result in engine misfires.
An engine misfire is when one or more of the cylinders aren’t firing (burning fuel and air) properly or fires at incorrect timing. In the case of a bad head gasket, it will often feel like the engine is hesitating as you try to accelerate. Here’s how to test your engine’s compression:
Keep in mind that when it comes to engine misfires, there are a few other possible (and less serious) causes. For example, a faulty spark plug or ignition coil will often result in an engine misfire. This is one of the most common causes since a lot of people often forget to change their spark plugs.
How To Tell If Head Gasket Is Blown
If you see more than one of the symptoms above, then it’s very likely you have a blown head gasket. Unfortunately, there’s no one true way to find out. Realistically, you can’t physically check the gasket because it’s installed inside your engine, and disassembling it will cost a lot of time and money.
So, the best you can do is check if you’re experiencing more than one of the symptoms above. If you have only one of the symptoms, then you may have a different issue that doesn’t relate to the head gasket. Here are some links you might find helpful:
Wait, how about the valve cover gasket then? What are the signs? Well, that segues us nicely to our next section:
Valve Cover Gasket Leak Symptoms
The most obvious symptom will be a dirty valve cover and engine. A valve cover gasket leak will likely leak the engine to the outside of the engine, and you’ll notice areas near the valve cover to be dirty and covered in oil. Since oil attracts debris, this should be quite obvious.
As mentioned, the valve cover is the uppermost part of your engine. If it seems the leak is coming from the top of your engine, you likely have a bad valve cover gasket.
Another symptom is a misfiring engine, and this is when you should start to worry. An engine misfire from a bad valve cover occurs when oil starts to seep into the spark plug tube.
Not only does this disrupt the spark plug’s performance which causes the engine to misfire, but it’s also a fire hazard. So, if you think you have a valve cover gasket leak, you’re going to want to repair that as soon as possible.
Blown Head Gasket Repair Cost
As we’ve established, an external oil leak can either be a head gasket leak or a valve cover gasket leak. Either way, this is a bad situation that you shouldn’t ignore and should fix right away.
If it turns out you have a bad head gasket, you’re going to have to spend between $1,000 – $2,000 to replace it. The head gasket itself typically costs between $200 – $500, but the labor is at least another $800.
This is because replacing the head gasket takes time and skill. It entails removing the top part of your engine such as the camshaft and cylinder head. Then your mechanic will need to clean the surface, fit in the new head gasket, and then reassemble the top part of your engine.
This process takes around eight hours to finish, and often more in some cars. So, you can see why the labor and total cost are expensive. If you have more questions, we recommend reading our article about head gasket replacement costs.
Meanwhile, if it turns out you have a valve cover gasket leak, this is usually much cheaper to fix. The total cost usually comes to about $350 for most cars, with the gasket itself costing around $50.
Blown Head Gasket Repair
With such an expensive repair cost, the question you’re probably asking now is can you do it yourself to save money? In the case of the head gasket, if you have to ask, then you probably can’t.
Replacing the head gasket is essentially dismantling and then rebuilding half of your engine. It’s a very difficult process and practically impossible if you’re not skilled and don’t have the right tools.
We generally recommend leaving this job to a professional. Even if you can do it, it’s easy to get something wrong during the process which can do more harm than good for your engine.
How about a valve cover gasket replacement then? Is that possible? Surprisingly, yes. While not quite as simple as, say, replacing a spark plug, replacing a valve cover gasket is realistically doable.
The difficulty may differ depending on your engine type, and your car’s make and model. For example, a bigger engine such as a V8 is usually more difficult than an inline-six engine. But we would say it’s still doable. Here’s an example to give you an idea of the process:
Valve Cover Gasket Replacement
Here are the steps to replacing a valve cover gasket:
- Remove the plastic engine cover, and then remove any hose and cable connections. This includes the vacuum line and the spark plugs and their connectors. If you have a distributor-type ignition coil, mark the cables in relation to the cylinders for when you reconnect them.
- Remove the valve cover bolts, and then the valve cover. If the valve cover seems to stick, gently tap it with a rubber mallet. Be careful not to drop anything into the engine after removing the cover.
- Remove the old gasket and its remains. You can use a plastic scraper to help remove it, but DO NOT use a metal scraper.
- Clean the surface with a clean rag. Use a wire brush gently if you have difficulties.
- Some cars may require you to apply silicone sealant or RTV, so check the service manual or gasket instructions to find out whether this is necessary or not.
- Install the gasket on the cylinder head. Take your time, and make sure it fits properly.
- Clean the cylinder head surface once again before reinstalling the valve cover on top of it. Make sure that it aligns properly, and you can hand-tighten a few bolts in the process.
- Once you’re sure everything is in place, properly tighten them. Make sure that you tighten them to the right torque spec – if applicable.
- Reconnect the hoses and cables. Let the car sit for at least 24 hours to allow the sealant to settle.
- Start your engine and let it idle for a few minutes and check for leaks.
Our guide is a bit of an oversimplification. We recommend watching the video above for the complete guide. Or you can also visit our valve cover gasket article to learn more.
Head Gasket Failures: Symptoms, Causes, and Prevention Facts
- The head gasket is the most over-stressed gasket in an engine, sealing between the cylinder head and engine block deck, and resists various forces like pressure, temperature, vibration, and shifting/flexing of the cylinder head.
- A blown head gasket can occur in several ways and can have varying degrees of severity depending on how and where the failure occurred.
- Testing engine oil and coolant regularly can help diagnose head gasket failures, and diagnosing a blown head gasket requires experience and a methodical approach.
- A leaking head gasket can cause oil to leak down the side of the engine or coolant to leak outside the engine, which can result in a low coolant level, overheating, and other problems.
- When the head gasket fails between the cylinder and oil gallery, hot compression gases will enter the oil system and pressurize the crankcase, causing a drop in engine oil levels and blue smoke from the exhaust.
- A blown head gasket between the oil gallery and coolant passage can cause milky, frothy sludge in the engine oil, leading to overheating and severe engine damage.
- A failure between cylinders can cause rough idling, misfires, and loss of power, while a failure between the cylinder and coolant passage can cause low coolant levels, sweet-smelling white smoke, and overheating.
- Routine oil and coolant testing can prevent coolant system issues, which are one of the leading reasons for engine overheating and can increase the potential for a blown head gasket.
- Coolant mixing with engine oil can reduce the oil’s lubricating properties, leading to engine failure, and if the oil leaks into the coolant, it can seriously degrade the coolant’s effectiveness.
- Early detection and quick reaction are critical to preventing more damage and catastrophic failure, and repairing a blown head gasket is expensive and not for the faint of heart.
Head Gasket Leaking Oil: In Conclusion…
So, to summarize, an external oil leak can mean that your head gasket is blown and is causing the leak. However, this is quite rare as most head gasket leaks are internal. It will either leak oil or coolant into the engine’s cylinders or mix the oil and coolant together.
Instead, an external leak more often means a valve cover gasket leak. If the leak seems to come from the middle part of the engine, then it’s likely a head gasket leak. However, if it comes from the top part of the engine, then it’s more likely to be a valve cover gasket problem.
In any case, oil is like blood; it’s supposed to stay inside of your engine. If you’re experiencing an oil leak, immediately find the cause and repair it as soon as possible. Low oil levels can cause excess wear to the engine internals. And an oil leak can even be a fire hazard in some cases.