Car Leaking Oil? Possible Causes and What to Do About It

Stephen Fogel
January 29, 2018

If your car is leaking oil, you’re not alone. Oil leaks are a common problem — we’ve all seen the dark stains in parking lots and driveways. But what creates them? And, more importantly, how can you stop them?

Oil is an essential fluid for the health of your engine, and it’s much better for your car, truck, or SUV it all stays inside, where it belongs. Unfortunately, it can work its way out and leak onto the engine or other parts, and then to the ground underneath. These leaks can simply be minor annoyances, or they can be serious threats to the life of your engine. It’s essential to know the difference so that you can avoid expensive repairs or getting stranded.

What your engine oil does

The several quarts of oil that circulate inside your vehicle’s engine perform many essential functions. Your oil does all this:

  • Protects against wear
  • Prevents corrosion
  • Keeps the moving parts from touching
  • Reduces friction
  • Transfers heat away
  • Carries away contaminants and debris 

The types of oil used today are a chemical mixture of base oil stock for essential lubrication functions and additives. These additives help your engine oil perform all the other requirements demanded by contemporary emission-controlled, hotter-running, fuel-efficient engines, such as: 

  • Reducing friction for improved fuel economy
  • Letting it flow smoothly at low temperatures
  • Preventing oil oxidation at high temperatures
  • Keeping oil from foaming in the crankcase
  • Protecting metal parts from corrosion caused by moisture and acids
  • Keeping it thick enough at high temperatures
  • Inhibiting the formation of deposits, rust and corrosion
  • Preventing the creation of oil sludge
  • Preventing wear if the oil does not lubricate properly

When oil leaks out, that means that you have less lubricant inside the engine, which can lead to serious problems down the road.

» MORE: How often should I change my oil?


What you can do about oil leaks

It’s essential to deal with an engine oil leak as soon as possible. Here’s why:

  • A small leak can turn into a large leak, which can lead to engine failure
  • Oil leaking onto the ground pollutes the environment
  • Oil on the ground is a slipping hazard, especially in a garage

As a precaution, you need to know how much oil has leaked out. Check your oil when the vehicle is on a level surface and cold, or let it sit for five to 10 minutes after driving it.

Pull the oil dipstick out, wipe it off, then reinsert it for a moment and pull it out again to check your current oil level. If it’s between the halfway mark and the “F” or full mark, you have enough oil. If it’s below the halfway mark, top it up — but don’t overfill it. After this, check your oil frequently to see how much you may be losing. If you can see the level dropping during these checks, keep it topped up and call your mechanic. 

Major leaks with large oil loss

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.

Minor leaks

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.

Warning signs that you have an oil leak

The most obvious warning sign that your engine is leaking oil is a dark brown puddle under the front of your car. You might notice it when you back out of your garage or driveway. 

However, most cars today have shielding under the vehicle. This shield will often catch the oil before it hits the ground, which can hide a potentially damaging leak. Checking your oil level every other time you gas up can help you identify an oil leak. 

Another way you might spot an oil leak is when you open the hood to check your vehicle’s fluids. You may see oil leaking or seeping from the engine in all sorts of places, and it could be getting everywhere. If your engine is covered in oil, it can be a serious fire hazard and needs immediate attention from your mechanic.

If the oil is burning from contact with hot engine surfaces, you might be able to smell it. You may notice it while driving, or when you get out of the car after you park it. This is another sign that your leak is a serious one. Call your mechanic. 

Common causes of engine oil leaks

The qualities that help your oil to flow through and lubricate your engine also let it escape through the tiniest of crevices. There are many potential sources and causes of oil leaks from your engine.

Your oil filter

Your engine’s oil flows continuously through your oil filter, which removes impurities from the oil. Most cars have a screw-on oil filter. If the oil filter has not been attached properly, or works its way loose, you can have an oil leak here.  

Your oil drain plug

Your oil drain plug screws into the bottom of your engine’s oil pan. It’s removed during an oil change to allow your old oil to drain out before the new oil is poured in. If the threads on the drain plug are misaligned or worn, or if the plug is loose or overtightened, oil can leak from here. Also, be sure the drain plug has the proper sealing ring and replace it during each oil change to ensure a tight seal. 

Your oil pan (and gasket)

Located at the bottom of your engine, your oil pan can be damaged by road debris. This can create a hole in the oil pan, which will cause a leak. The pan’s gasket can also wear or get damaged, causing oil to seep out.

Your oil filler cap

This is the large, round, removable cap on top of your engine. It usually has a symbol of an oilcan on it. This is where fresh oil is added during oil changes, or when you need to top up your oil level. If the filler cap is loose, or missing, or its seal is worn, the pressure created when the engine is running can cause an oil leak there.

Your oil cooler lines

Many vehicles have external oil coolers. These are small radiator-like devices placed in the airstream at the front of the vehicle. The part’s purpose is to cool down the hot oil, which circulates through the cooler before returning to the engine. Damage to or corrosion of the lines running to and from the cooler can be a source of oil leaks. 

Your valve cover gaskets

Valve covers are, as the name implies, protective covers that attach around the valve assemblies. Your valve covers keep the oil that lubricates the entire valve assembly inside the engine, where it can circulate.

Between the valve covers and the cylinder head where they attach, there are gaskets that provide a seal between these two components. Over time, these gaskets can corrode and deteriorate, allowing a leak to develop. This process is sped up if you don’t change your oil regularly.

Other gaskets and seals

More gaskets and seals are found between the metal surfaces of your engine. In addition to the ones on the oil pan and valve covers, there’s a timing chain or belt cover gasket and head gaskets. There are camshaft seals and the rear main seal around the crankshaft. These can also be sources of leaks.

Failure to change your oil at recommended intervals

Your oil deteriorates as it ages, producing sludge and other corrosive substances. In addition, dirt, abrasive particles, metal fragments and byproducts of combustion accumulate in your oil over time. If your oil isn’t changed, these items can remain in the engine long enough to wear on gaskets and seals, causing them to fail. 

Even if you’re comfortable changing your own oil, it’s a good idea to get it done by a certified mechanic every so often. The professionals may be able to spot oil leaks or other issues before they become bigger and more problematic.

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.