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We all know that our car’s engine burns fuel to produce the power we need to drive it to where we go. But when somebody tells us that we’re burning oil, what exactly do they mean? For newbies, burning oil can be a sign of an impending costly repair. For seasoned car owners who know their vehicles by heart, burning oil requires a more thorough evaluation before taking any concrete steps toward its resolution.

oil cap

Burning Oil?

When they say your car is burning oil, they usually mean that you have a leak somewhere in this closed system. If oil escapes into an area where it should not go, then you are burning oil? Why? Well, the passageways for oil are somewhat hot. If you put oil into a hot surface, it will increase its internal temperature and burn.

There are two fundamental types of burning oil: one that occurs outside the engine and another occurring right inside the engine’s combustion chambers.

Why is There Oil Burning Inside My Engine?

We mentioned above that burning oil can happen anywhere there is contact between motor oil and a very hot surface typically caused by a leak in the system. If your car is burning oil internally, meaning it occurs inside the car’s engine, this is usually caused by a number of things.

  • Problems with the PCV

One of the potential causes of internal oil burning is a malfunction in the positive crankcase ventilation system or PCV. If the PCV valve is blocked, it will not be able to push a small amount of air-fuel mixture known as blowby back into the engine. This blowby remains in the crankcase and can lead to dilution of the motor oil. At the same time, pressure inside the crankcase is increased, forcing motor oil into the cylinders of the engine where it is burned. The increase in crankcase pressure can also lead to blown gaskets and seals. This can further increase the risk of burning oil within the engine itself.

The PCV valve also separates oil so that the latter will not go inside the combustion chambers. If the PCV valve is damaged, the oil will not be separated from the blowby gases. As the PCV returns, these blowby gases back to the engine for reuse, oil goes with these gases and gets burned by the engine.

  • Worn-out Valve Seals and Guides

Both the intake and exhaust valves of your engine come with guides and seals, keeping engine oil out of the combustion chambers. Unfortunately, these do not really last a lifetime. They are subject to wear. When this happens, they may no longer prevent oil from gaining entry to the combustion chambers, leading to oil burning within the engine itself.

One of the classic signs of possible valve seal failure is bluish smoke that comes out of your tailpipe especially right after starting. This is almost always an indication of internal burning oil. The bad guides or broken or damaged seals allow oil to seep through into the engine’s combustion chambers. As you start your engine, this oil is burned leading to that characteristic blue smoke.

  • Damaged Piston Rings

Piston rings have the same function as valve seals, except that they form just the right amount of seal between the engine’s pistons and the bores of the cylinders. It should not be too tight to still allow a thin film of oil to seep through so that the surface between the pistons and the cylinders are well-lubricated. It shouldn’t be too loose so that oil will not get past the cylinders and get burned together with the mixture of air and fuel in the combustion chamber.

If the piston rings are damaged, there is a much wider space between the bore surface and the piston. This allows more oil to pass through the piston and get burned in the process. If the blue smoke in your tailpipe is most evident during acceleration, you may have a problem with your piston rings.

To recap, oil burning internally can be caused by a problem in your PCV valve, worn-out valve seals and guides, or even a substantially worn-out or damaged piston ring.

check car oil

Why is There Oil Burning Outside the Engine?

Aside from the characteristic smell of burning oil, another thing that can characterize oil burning internally is the presence of blue smoke upon starting your vehicle (as a sign of valve seal or guide problem) or during acceleration or deceleration (piston ring or PCV valve issue). If you don’t have this blue smoke and yet you smell burning oil, there’s a chance that the issue is an externally burning oil. The fundamental reason why this occurs is that oil escapes from somewhere and lands onto a hot surface on the underside of your car. Let’s look at the potential sources of these leaks.

  • Improperly-attached Oil Filter

During an oil change, the oil filter has to be replaced as well. Unfortunately, if the new oil filter has not been attached or screwed on tightly and securely, there’s a chance that oil will leak out through it. This can land on some parts of the engine bay where, while it may not be as hot as the inside of an engine, oil can burn because of the hot surface.

  • Loose or Ill-fitting Oil Drain Plug

When changing the motor oil, there must be a mechanism to remove the old oil from the engine. This is the function of an engine oil drain plug. Opening this will help drain old motor oil back. When you’re ready to replace it with new oil, the plug has to be returned and screwed on tight. Sadly, there are instances when the oil drain plug is not secured properly. This can be a cause of an oil leak.

  • Damaged Oil Pan

The engine oil pan is typically located at the bottom of the engine. There are instances when the oil pan gets damaged because of being hit by road debris like rocks and other hard objects. It is also possible that the gasket surrounding the oil pan can wear out over time. Again, this can cause oil to leak out. If there are no hot surfaces directly underneath it, then you will not have any issues with burning oil.

  • Loose, Missing, or Worn-out Oil Filler Cap

The oil filler cap is located right on top of the engine. It covers the large hole where you pour your engine oil in whether to replace it or to top it up. It should form a tight seal around the opening to maintain pressure needed by the oil to circulate throughout the system. If the filler cap is already worn-out, loose, or worse, missing, then there’s no mechanism to stop the oil from getting pushed outwards. And since it is on top of the engine, oil can creep on the surface and can get burned by the hot engine surface.

  • Damage to Oil Cooler Lines

If your vehicle came with an external oil cooler which is like a very small radiator placed in front of your car to cool down the motor oil before it gets recirculated to the engine, there’s also a possibility that the leak can come from here. These oil cooler lines can get damaged or even corroded.

  • Damage to Valve Cover Gaskets

Valve cover gaskets form a protective seal between the cylinder head and the valve covers; hence, the name. These can degrade over time which can cause oil to leak outside the engine and produce that characteristic smell of burned oil.

External oil burning occurs because of a leak in any one of the components outside the engine that have a role in motor oil circulation. Having these checked is crucial if you want to identify the exact cause of oil burning.

fill car oil

How Can I Fix It?

Understanding the exact cause of burning oil, whether internally or externally, is crucial to determining the best course of action.

For internally burning oil, the PCV system’s mounting elements and hoses can be replaced if this is the cause of the problem. If the PCV valve itself is already at fault, usually because of sludge buildup, then this can be easily fixed by a thorough cleaning by a professional mechanic. If the issue is in the valve seals and guides, then these must be replaced, too.

The main problem is if the piston rings are already damaged. Generally, this requires a complete engine rebuild. It’s a tedious process and very expensive at that. Alternatively, you can look for a suitable replacement engine. Damaged piston rings usually signify the end of service life of the car’s engine. So you might want to think about having the engine rebuilt, replaced, or simply get another car.

For externally burning oil, the fixes are pretty straightforward such as tightening and securing the oil filter, oil filler cap, and oil drain plug. These can be replaced as well if they are already damaged. You can also replace damaged valve cover gaskets, seals, and the oil pan.

A car burning oil is not usually a very serious problem if the cause happens to be from outside the engine. But if the culprit is already within the engine itself, you’re looking at a mighty costly proposition.

Sources:

  1. What Does It Mean When My Car Is “Burning” Oil? – YourMechanic
  2. Oil Changing Frequency – howstuffworks

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