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Is Your Car Burning Oil? Here’s Why, Plus Ways to Fix It

Stephen Fogel
February 9, 2018

When you hear about or experience a vehicle burning oil, it can mean a few different things. It might be pretty normal — or you might be in urgent need of a certified mechanic. Let’s find out how to tell the difference.

car burning oil

Your motor oil has several functions. It lubricates the moving parts inside the engine, preventing harmful metal-to-metal contact. It also removes dirt, metallic particles and other bad things from the inside of the engine as it travels through the oil filter. Additives in the oil prevent corrosion and improve the oil’s performance.

The tight tolerances between metal parts inside your engine, as well as certain gaskets and seals, are designed to keep your oil where it belongs. But these elements can wear or fail, allowing oil to go where it shouldn’t. This can progress to the point where where your vehicle is burning oil.

What does ‘burning oil’ mean?  

Normal oil consumption

First things first: Just because your car is consuming oil, that doesn’t mean it’s burning it in a harmful way. Modern vehicles use thinner motor oils that reduce friction and produce better fuel economy — and sneak through gaskets a little more easily. Some manufacturers advise owners that normal operation will result in a significant amount of oil consumption. These carmakers state that you may need to add several quarts of oil in between scheduled oil changes. It’s important to check your engine’s dipstick to make sure you’re not running low on oil.

Oil that leaks externally and burns

This burning oil situation is more serious. It usually results from an oil leak somewhere on the exterior of your engine. This oil then finds its way to hot engine surfaces, like the exhaust system, where the intense heat can cause the oil to smoke and possibly ignite. You can usually observe this if you raise the hood when the engine is at full operating temperature. You’ll want to get any oil leak fixed to prevent bigger problems.

Oil that leaks into your engine’s combustion chambers

This is the most serious type of “burning oil” problem. As engines age, they wear. Their internal seals and gaskets can fail and cause an oil leak that can be hard to notice. This oil can travel to the combustion chamber, along with the air-fuel mixture, and be burned. If you see bluish smoke coming from your exhaust, this is a telltale sign that your engine is burning oil internally. 

If your car has this type of problem, you’ll want to get it to a mechanic quickly. Depending on the exact cause, you may be able to get your vehicle fixed without major expense. But if you let it go, you could be in for a big repair bill.

There are many downsides to an engine that burns oil. Letting the oil level get too low can lead directly to engine failure. Too much oil in the exhaust can destroy your catalytic converter, an expensive item to replace if it’s not under warranty. You can lose power and fuel economy. Your vehicle may not pass its emissions test.

Causes of oil burning externally

Oil can leak out of your engine at a number of points. Various components can deteriorate, wear out or become misaligned. Seals and gaskets can also wear or fail. Any of these causes can allow oil to escape from the engine. When the leaking oil comes into contact with a hot exhaust manifold, it can burn, producing smoke or fire.

We cover common sources of external oil leaks in more detail here, but in general, they are your:

  • Oil filter
  • Oil drain plug
  • Oil pan (and its gasket)
  • Oil filler cap
  • Oil cooler lines
  • Valve cover gaskets or other gaskets and seals

If you’re losing a lot of oil quickly, you must get your car to a mechanic immediately. You may want to have your vehicle towed there if the leak is so bad that you can’t drive it safely.

Smaller leaks may be less urgent, but they still will require your attention. If the source of your oil leak is the oil filler cap, you can buy a replacement at your local auto parts store, or at a dealership parts department. 

If your leak is coming from the oil filter, and you know how to change your own oil, you can replace the filter with a new one. After you drain the old oil, remove the old filter and make sure its seal doesn’t stick to the engine. Then thread the new filter on carefully and tighten it securely. Be sure to correctly insert and tighten the drain plug, as well. Then add the new oil. 

For other sources, you may be best off having a mechanic take a look.

Get it diagnosed by a professional
 

Causes of oil burning internally

There are a few different frequent causes of oil burning inside your engine. We have organized them in from easiest and least expensive to fix, up to major engine repairs. Here we go:

PCV system: The positive crankcase ventilation (PCV) system handles the small amount of air-fuel mixture that gets by the cylinders and enters the crankcase during engine operation. It sends this mix, called blowby, back into the engine to be burned efficiently. 

The PCV system uses a one-way valve so that the blowby is unable to return to the crankcase to cause problems. The oil is also separated out so that it does not travel into the combustion chambers and get burned.

A malfunction in the PCV system can cause one or more of the following oil-burning problems:

  • A blocked PCV valve can keep the blowby gases from leaving the crankcase, resulting in gasoline diluting the oil, pressurization of the crankcase, and oil being forced into the cylinders, where it is burned.
  • Pressurization of the crankcase can also lead to blown seals and gaskets, worsening any tendency for the engine to burn oil.
  • Failure of the oil to properly separate from the blowby gases, which can allow oil to travel along with these gases, and then get burned in the combustion chambers.

Valve guides and seals: Your engine’s intake and exhaust valves help ensure that your engine runs smoothly and performs well. The intake valves let the air-fuel mixture into the cylinders, and the exhaust valves allow the burned mixture to exit the cylinders. 

This system is lubricated by motor oil, which is supposed to stay out of the combustion chambers. When the engine is new, and when it has been properly maintained, the valve guides and seals keep the oil away from the combustion area. But on older engines, or those that have not been well maintained, these valve-related parts can wear and fail. When that happens, they can allow oil to enter through the valve openings, where it is burned in the combustion chambers.

If you see that distinctive bluish smoke coming from your exhaust, primarily during start-up, the valves may be your source of burning oil. The oil drips down from the valves’ bad guides or seals into the combustion chambers while the vehicle is parked. The oil then gets burned when you start it up. This can also happen under strong deceleration, as the high level of vacuum in the intake sucks oil through the leaky valves. 

Piston rings: Your piston rings form a seal between the pistons and the cylinder bores. This seal is loose enough to let a thin film of oil come up from below and lubricate the cylinders as the pistons move back and forth. It is also tight enough to keep too much oil from entering the cylinders and getting burned along with the air-fuel mixture.

If the piston rings wear down, too much oil can enter the cylinders from the crankcase below and be burned. The worn piston rings can also send some combustion pressure down into the crankcase, where it can create problems that are similar to a PCV system malfunction. 

If you notice blue smoke while you are accelerating, the source of your burning oil is likely worn piston rings. 

What can I do if my car is burning oil? 

If your vehicle is burning oil — especially if you suspect it’s being burned internally — it’s crucial to get it to a mechanic right away. The more oil that gets burned in the combustion chambers, the more your engine will be damaged. 

As a starting point, it’s essential to know how much oil your engine is burning. The best way is to check your engine oil level at frequent intervals. You should check the oil when your vehicle is on a level surface and cold, or you can let it sit for five to 10 minutes after driving it — say, at every other gas fill-up.

Pop the hood, pull the oil dipstick out, wipe it off, reinsert it for a moment, and pull it out again to check the current oil level. Make a note or take a picture, then compare as you repeat this process over the following days or weeks. If it’s consistently dropping, it’s time for a visit to the mechanic. 

Fixing oil burning outside the engine

Your oil filler cap or oil filter may be the source. Replacing these items will usually solve the problem. Make sure that the oil filter is properly screwed on and tight enough.

Another common source is the valve cover area. The valve cover protects the valve mechanism, which is usually on top of the engine. It also retains all the oil that’s used to lubricate the valvetrain components. A failed gasket between the valve cover and the head can be the source of the leak. The bolts that retain the valve cover may also be loose. Most engines have either one or two valve covers, depending on the type of engine.

This is a starightforward fix, but a messy one. You'll need to get the valve cover gaskets replaced. It’s a good idea to check the other engine gaskets and seals for leaks that may result in burning oil. If one has gone bad, the others may be about to go. 

Fixing oil burning inside the engine

Depending on the exact cause of your engine’s internal oil burning situation, the fix can range from fairly simple and inexpensive, to extremely complex and very expensive. Let’s start with simple and work our way up.

PCV system: If the PCV system is the source of your oil burning problem, the remedy is fairly straightforward, not too expensive, and with minimal downtime.

If the PCV system’s hoses and mounting elements are at fault, they can be swapped out. Be sure to use hoses made specifically for the PCV system — they are designed to operate properly under vacuum, not under pressure like other types of automotive hoses.

The PCV valve can also be at issue. Sludge can build up and make the valve stick in the open position. This can allow too much oil to pass through and enter the engine, where it is burned. It’s an inexpensive part, but the job should probably be left to your mechanic, as the PCV system is complex, with many pieces.

Valve guides and seals: We have good news and bad news here. If the oil-burning problem in your valve system is limited to your valve seals, it’s not serious. There will be some labor involved, but the seals can be replaced without the need to tear down the motor.

If you need to replace your valve guides, on the other hand, it’ll be significantly more expensive. The heads will have to be disassembled so that the new valve guides can be installed. The amount of labor required is much greater, and the parts cost is higher as well. There will also be some downtime for this repair, so arrange alternate transportation.

Piston rings: If worn-out piston rings are the source of your vehicle’s oil-burning issues, you have a serious problem. Your engine has reached the end of its service life. The remedy is typically a complete engine rebuild. Yes, it’s very expensive. It also takes a lot of time. 

One alternative is a replacement engine. You may be able to find one in a junkyard, from an automotive recycler, or from a company that remanufactures engines and sells them with a limited warranty. It all depends on what your car is worth and how much more you’re comfortable investing in it. 

If your vehicle is old and has high mileage on it, it may not be worth fixing. Get an estimate and have a talk with your mechanic.

Stephen Fogel

About the Author

Stephen has been an automotive enthusiast since childhood, owning some of his vehicles for as long as 40 years, and has raced open-wheel formula cars. He follows and writes about the global automotive industry, with an eye on the latest vehicle technologies.

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