One of the last things you want to hear from a mechanic is that the head gasket in your engine is leaking. This can be an extremely expensive job to get fixed and, for most drivers, it's hard to figure out why. The fact of the matter is that most casual automobile owners really don't know much about how their engine functions and what all the parts do. Head gaskets are one of those components that, while you may be familiar with the name, it's entirely possible you don't know what they do or why they might have a problem in the first place. So, let's take a look at why your head gasket might be leaking oil externally, if it really is the head gasket at all, and what you can do about it.
What is a Head Gasket?
Many drivers are surprised when they see a head gasket for the first time since it looks like such a small and insignificant part of the engine. The head gasket is located between the cylinder head and the engine block. It’s very thin and full of holes to accommodate the cylinders which makes it look like it may not be very important.
Typically, a head gasket is made from layers of steel and elastomer. In older cars this may have been made from graphite or asbestos. When it seals in place it ensures the combustion chamber is sealed and prevents oil and coolant from leaking. Without a head gasket in place the combustion reaction will either not be able to take place or will be contaminated with too much air or not enough pressure preventing your engine from producing enough power to work properly.
A functional head gasket also ensures a cleaner running car. Harmful gases are forced into your exhaust rather than leaking from the engine into the air. Although modern head gaskets are far more durable than old school graphite and asbestos ones, they can still fall victim to wear and tear or mechanical failure and end up failing.
What Would Cause a Head Gasket to Leak Oil?
When your head gasket starts leaking it’s often referred to as being blown. A blown head gasket can no longer maintain a seal and that means it’s unable to maintain pressure and keep fluids contained.
Overheating: There are a handful of causes for a blown head gasket but by far the most common cause is an overheating engine. Although a head gasket is designed to handle high temperatures, if the heat in your engine gets beyond what it was designed to handle, it will cause the head gasket to wear down much sooner. Because a head gasket is made of metal, the heat will cause it to expand and it will contract again when the engine cools down. When this happens over and over again, it will eventually fail completely.
Pressure: If you're suffering from some pre-ignition problems and the timing of your combustion reaction is off, it can cause too much pressure to build up in the cylinder head. Just like excess heat, this excess of pressure can cause your gasket to fail as well. When this is the case, you'll notice that your engine seems to be running very rough especially at start-up or when it's idle.
Coolant pH: You need to maintain the integrity of your coolant in your engine in order to keep it running at optimal temperatures. Since heat can cause a blown head gasket, it stands to reason there may be a problem with your coolant as well. If your coolant becomes too contaminated overtime in from not being changed regularly, the pH balance will be off and the acidic nature of it can cause your gasket to wear down sooner than it should. Likewise, this can lead to problems with electrolysis wearing down your gasket as well.
Regardless of what caused your head gasket to blow, if it's no longer able to maintain a proper seal then you could start having oil leaking. The thing to remember here is that a blown head gasket typically causes oil and coolant to leak and mix together internally, not externally.
One thing that is worth knowing in this case that while there is a difference between when your head gasket is leaking oil internally and leaking oil externally, a head gasket leaking oil externally is actually very rare.
Is Your Head Gasket Really Leaking Oil Externally?
Typically, when you think your head gasket is leaking oil externally the problem is actually related to a valve cover gasket, an intake gasket, the external oil supply tube itself, or a galley plug. These can often be misdiagnosed as the source of an external oil leak from a head gasket. All that being said, it's not impossible that your head gasket is leaking oil externally, it's just very unlikely. So, if you are suffering from an external oil leak make sure you check out those other issues first. Like we said, this can be very commonly misdiagnosed and even a qualified mechanic may overlook these problems.
Valve Cover Gasket Leaks: If you have a valve cover gasket leak then you're going to have an oil covered valve cover and potentially the smell of burning oil as a result when you're driving your car. The oil from the valve cover will hit your exhaust manifold and cause it to burn. This is the most common cause of oil leaking down the sides of your engine that you might mistake for a problem with your head gasket. Just like your head gasket, the valve cover gasket is prone to wearing down and breaking after exposure to heat, dirt and debris overtime.
Intake Gasket Leaks: Your intake manifold has gas gets around it that help seal oil and coolant as well. Not every engine is built the same way so not every intake manifold gasket will leak oil, sometimes it will leak coolant, sometimes neither, but it is possible that if your intake manifold gasket has been damaged oil will be leaking out and can potentially trick you into thinking it's coming from the head gasket.
Oil Galley Plug Leak: You won't find this in every engine either, but oil galley plugs are used to fill holes that have been drilled in the front of the engine block to allow oil to be sprayed on to the timing chain during operation. The plug can be used to drain out that area, and to allow for cleaning. However, the dowel pin that fits in the plug can wear down and cause leaks over time.
Oil Line Leak: Oil travels through your engine through a series of tubes and any one of those could be subject to a leak where it connects one component of your engine to the other. Even the line itself could get damaged with a small crack or hole and start leaking. Depending on the location, this could also leak on the engine in a way that tricks you into thinking it's a head gasket leak when it's not.
How Do I Know if My Head Gasket is Leaking Oil?
If you truly do have a problem with your head gasket there are a handful of signs and symptoms you can be on the lookout for it to let you know there's a problem. Like we said when you notice an external oil leak it’s not typically a symptom of this particular problem, but it definitely can happen. For more common symptoms, these are the things you should be on the lookout for.
Overheating: Just as this is a cause of a blown head gasket, it's also going to be a symptom as well. If your engine is constantly running into the red, you may have a blown head gasket. Because your engine can't receive the proper amount of oil or coolant any longer, it's going to be running hot far more often.
Bad Oil: If there truly is a problem with the oil as a result of your head gasket springing a leak what's going to happen is your oil is going to be contaminated with coolant. The result of that is when you pull out the dipstick to check your oil it's actually going to be milky white rather than the colour you're expecting. The colour and texture resemble a milkshake and it's pretty unmistakable. The same thing will happen to your coolant reservoir because you're going to get oil mixed into the coolant.
If you noticed your oil contaminated in this way you need to get to a mechanic as soon as you can. Driving your car with coolant contaminated oil will cause serious damage to the bearings fairly quickly, not to mention leading to problems with overheating.
White Smoke: When your head gasket has failed you run the risk of burning coolant through the exhaust of your vehicle. That's going to produce a noticeable white smoke out of the back of your car, typically with a distinctive sweet smell to it as well. When the coolant slips past the faulty gasket into the cylinder it will boil off into steam very quickly and then be expelled as white smoke from the back of your car. If you have oil leaking into the combustion chamber and burning, then the smoke produced by your exhaust is going to have more of a bluish grey colour to it.
If your external oil leak is accompanied by any of these symptoms, then you have a much stronger case for a blown head gasket being the cause of the oil leak in the first place. If none of these other things are happening, then you want to potentially look at the initial causes of an external oil leak that we mentioned.
Blown Head Gasket Repair Cost
if you truly do have a leak coming from your head gasket because the gasket is damaged then you're going to need to get a replacement. Taking it into a mechanic is going to set you back between $1,000 and $2,000 to get repaired.
If you head to AutoZone, you can find a new head gasket for between about $15 and $50. The bulk of that repair cost is labour charges because replacing a head gasket means taking your engine block apart which can be upwards of a 6-hour job depending on the make and model of the car you're driving. For that reason, if you can do any maintenance ahead of time to prevent your head gasket from experiencing that much wear-and-tear it's definitely in your best interests to do so.
How Do You Stop a Head Gasket from Leaking Oil?
As we've seen head gasket failure is most often the result of an overheating engine. So, if you stick to a routine maintenance schedule of changing your oil and coolant when it's required you can do a lot of work towards ensuring that your engine doesn't have to hit those high temperatures that are going to be damaging to your head gasket.
Your owner's manual will let you know for sure exactly how long your engine can go before you need to have your oil replaced. A lot of people use the standard rule of thumb of changing it every 3000 miles but that's not necessarily the right thing for every model of car. Some cars can go as much as 15,000 miles or more without needing an oil change if they're running on synthetic. Your owner's manual is always the best source for determining what's going to keep your car running optimally.
Likewise, you need to make sure you're changing the coolant when the owner's manual suggests as well. The longer you let it go, the more likely your engine is to overheat and the more your head gasket is going to be exposed to coolant that has an unbalanced pH which will cause even more damage.
The Bottom Line
Although it's possible that your head gasket could be leaking oil externally it's one of the rarer symptoms of a problem with a blown head gasket. There are a number of other signs to indicate you have an issue with your head gasket that you should be on the lookout for first. If your only symptom is an external oil leak and none of the others, then you may want to check into a different source of the problem that has been misdiagnosed as a problem with your head gasket. Given how expensive the repair job is, it's always a good idea to get a second opinion if you're not 100% sure so you can save yourself some time and money in the long run.