Oil leaks cause all kinds of issues, from burning smells inside the car to major engine damage. An oil leak is a common problem that many car owners face at some point in vehicle ownership.
In this article, I’ll expose common engine oil leaks and give you some tips to help diagnose exactly where your car is leaking. Then let’s shift gears to give you more insight on what it will take to fix it.
Here’s what will cover
Some Key points in this article
- Keeping up with routine vehicle maintenance goes a long way in preventing oil leaks.
- A leak that hits the floor indicates a large leak and should be looked at ASAP.
- A leak isn’t always a seal or gasket, high crankcase pressure can greatly amplify or cause an oil leak.
My Car Has An Engine Oil Leak, should I be concerned?
Not all oil leaks are huge, many in fact can go on for a long time before becoming a real issue.
So YES, an oil leak is a big deal, however the severity varies. If you are seeing drips of oil under the car it’s a good idea to have it checked out.
Even if it’s not terrible yet, it will only get bigger.
The Bottom line: If you notice an oil leak on the ground chances are it’s substantial and you should have it checked ASAP.
More than just engine damage
Did you know an oil leak will damage rubber components on your car, such as hoses and suspension bushings?
Yup!
If oil consistently leaks onto rubber components, it will cause the rubber to soften and swell. This causes all kinds of issues, including swelled hoses, suspension bushing failure, and even electrical issues in rare cases.
In my 25+ years of experence fixing cars, I have replaced quite a few swollen control arm bushings and coolant hoses because of oil leaks ruining the rubber.
Money that would never have been spent if the customer had the oil leaks fixed when they were first noted.
Why is engine oil so important?
Engine oil is essential for lubricating the internal moving parts of your engine.
Engine oil is a sacrificial fluid that fills tiny gaps between internal engine components. It takes a beating to keep the wear off of the metal parts inside the engine.
This is a big reason why engine oil breaks down and becomes black over time, it has sacrificed itself to protect the engine and it loses its ability to protect over time.
Without oil, an engine will suffer major damage in a relatively short timeframe. As you can probably imagine, if this stuff is leaking out of your car, eventually there will be little left to protect your engine.
There are several common causes of engine oil leaks, and they can sprout from different parts of your engine.
- Engine oil pan
- Rear engine seal
- Valve cover gaskets
- Oil filter housing
- Oil cooler lines
- PCV breather components
Common Causes of an Oil Leak
Now that you know common issues that cause an oil leak, let’s break them down so you can pinpoint which one is spilling black gold all over your driveway.
1. Oil Leak around the Oil Pan
One common cause is a leak around the oil pan. The oil pan, or “oil sump” is located at the bottom of the engine and holds all of the engine’s oil.
The oil pan is bolted to the main engine block and has either a gasket or specialized sealer to seal the two mating surfaces.
As you can imagine, this gasket or sealant bead is a prime place for engine oil to leak. Over time gaskets break down and the sealer loses its ability to seal properly. This is caused by multiple temperature variations over the life of the car.
Constant expansion and contraction as your engine runs hot and then cools completely overnight takes its toll.
Eventually, it can’t hold back the oil in the pan and a leak ensues.
Like many oil leaks, an oil pan leak usually starts as a small “seepage” that slowly turns to dripping on the ground.
Unless you have a cracked or punctured oil pan, then it’s just a big ass oil spill.
How to Tell If Your Oil Pan Gasket Is Leaking
The easiest way to check for a leaking oil pan is to visually inspect the underneath of your engine. If you see the oil dripping off the bottom of your engine it may be an oil pan that’s leaking.
Use a flashlight to look higher up from where the pan and engine meet. If there is no oil running down from a higher source chances are your oil pan is leaking.
2. Leaking Rear Main Seal
Another place oil leaks like to show up is in the area between the engine and transmission.
This is usually caused by a leaking rear main engine seal.
The rear main seal stops oil from leaking out at the rear of the crankshaft.
The rear of the crankshaft is where a flexplate or flywheel mounts, this allows the transmission to receive the engine’s power and propel you down the road.
Because the transmission bolts to the rear of the engine you can’t see the rear main seal unless the transmission and flexplate are removed. You won’t notice this leak until oil is leaking from between the transmission and engine mating surface, like in the picture above.
Fixing a leaking rear main seal is one of the more involved repairs due to the fact the transmission needs to be removed. It can also be hard to pinpoint where the leak is coming from exactly and sometimes you just need to pull the transmission to inspect it.
How to Spot a Rear Main Seal Leak
The biggest indicator of a rear main seal leak is oil dripping from the transmission bell housing area, right where it meets the engine block.
To check you will need to crawl under the car again with a light.
Take a look at the area where the transmission bolts to the engine. If the rear main is leaking you won’t see any external dripping or running down the block from a higher source.
The oil makes it’s way past the mating surface because oil is pooling up, and slowly running out from between the transmission and the engine block.
3. Leaking Valve Cover Gaskets
Valve cover gaskets are probably the most common cause of oil leaks.
The valve covers are usually the highest point of the engine that has oil. When valve covers leak there is usually oil everywhere, this is because the oil runs down from the cover, (or covers) and gets blown around by airflow while driving.
If you smell burning oil when you turn on your heat or A/C, this usually indicates an engine oil leak at the valve covers.
The smell of burning oil is from the valve cover dripping oil onto the hot exhaust manifolds, literally burning the oil.
This can also be a dangerous situation, oil and hot manifolds aren’t the best of friends, also keep in mind when you smell the burning you are breathing in fumes from burning motor oil.
Replacing valve cover gaskets varies greatly from car to car, some cars are easy on and off. While others are extensive jobs that require the removal of high-pressure fuel lines and other components.
How To Spot a Valve Cover Leak
The biggest sign your valve covers are leaking is a burning motor oil smell when running the car with the heat or A/C on.
You can find the leak by opening the hood and looking for oil residue around the valve covers and staining on the exhaust manifolds.
A quick tip: Motor oil is filled through one of the valve covers, if you smell burning after a recent oil change a little oil may have been spilled while filling, or the oil cap might not be installed properly.
If your car has multiple signs of an oil leak, otherwise known as oil drips everywhere … (I’m talking to you BMW and Audi Guys,) start with replacing the valve covers if they show any signs of leakage.
The best way to fix ANY oil leak is to start at the highest point, ie the valve covers, and work down.
The best way to fix ANY oil leak is to start at the highest point, ie the valve covers, and work down.
4. Oil Filter Housing or filter
Using a poor-quality oil filter can cause oil leakage as well. They usually come with cheap o-rings and seals.
Engine oil is filtered by getting pushed through the oil filter by oil pump pressure.
This removes any contaminants.
When you use garbage oil filters the filtration level is much lower.
Not only that, the filter material will even begin to break up and send pieces through your engine.
Trust me, steer clear of cheap oil filters.
Why an Oil Filter housing leak can turn large fast
Because of this pressure when an oil filter gasket leaks, it’s usually a big leak.
This is why you see the quick lube memes that show oil puking out of a customer’s car in the parking lot. It’s because the rookie oil changer usually leaves the old oil filter seals on, causing a massive leak.
The good news is it’s usually caught by the guy when he pulls the car out of the bay and sees the massive oil slick underneath your car.
Many cars have a cartridge filter and an oil filter housing that requires the replacement of o-rings and gaskets as they harden over time.
How To Spot a Leaking Oil Filter or Housing
Check the oil filter area and see if you notice oil around the area or on the filter itself. One tip is to never reuse oil filter o-rings, they will harden over time and create a big leak. Reusing these o-rings can even cause low oil pressure.
5. Oil Cooler Lines
Your vehicle may have oil cooler lines and a separate oil cooler. These lines usually have metal connections that have rubber lines in between held by hydraulic crimps.
These tend to drip oil over time, especially on many GM vehicles. This leak is usually found as slight drips on the ground that get progressively worse over time.
These lines do have pressurized oil flowing through them, if they are starting to leak it’s a good idea to replace them before they blow out completely and paint your garage floor black.
Checking Oil Cooler Lines
Locate the oil filter housing and the lines are sure to be close, use a light and follow the lines to the external cooler. Look for drips at the connections and or seals.
Some vehicles have oil coolers that bolt to the engine instead of using lines, an example is the BMW N55 engine. In this case, you will see oil running down from the housing. On BMW this can cause engine belt damage as well.
6. Faulty Gaskets and Seals
Different gaskets and seals are responsible for sealing different parts of the engine.
Over time, these gaskets and seals can deteriorate, become damaged, and more commonly harden up, leading to oil leaks.
Rubber o-rings and gasket material will lose their flexibility due to constant stress and oil vapor. This is why changing your engine oil at the right intervals is so important as old worn-out oil creates nasty vapor inside of the crankcase that damages seals.
Fixing an oil leak caused by faulty gaskets or seals is pretty straightforward, the bad seal or gasket will need to be replaced. This can be as easy as a 10-minute job, or as intricate as a 20-hour project depending on the cars and what is leaking.
It is critically important to use high-quality replacement parts to ensure a proper seal and prevent future leaks.
Especially if it’s a huge job to get at the leak.
How to spot bad gaskets or seals
In many cases, while you are trying to find the source of the leak the suspected area is already covered in oil and dirt.
Use a multipurpose solvent or de-greaser to clean the area down and then run the car while watching the mating surfaces of the suspected leak for seepage.
You may need to drive the car as well to gauge how active the leak really is.
7. A Damaged Oil Pan
A damaged oil pan will cause oil leaks.
The oil pan can become damaged due to road debris, improper installation, or corrosion and rot over time.
Symptoms of a leak caused by a damaged oil pan include active oil leaking or consistent dripping.
To fix an oil leak caused by a damaged oil pan, the damaged pan will need to be replaced.
This can be a more involved repair as it may require removing other components to access the oil pan and remove it from the car.
If you tackle this project yourself be sure to properly clean the mating surfaces, always use good quality parts, and torque fasteners to specification.
Inspecting The Oil Pan
You will have to get underneath your car and check the oil pan for hairline cracks and rust blistering.
Sometimes the pan rots in spots that you can poke with a screwdriver and go right through! I’ve seen this most commonly on Nissan, as a side note Mercedes Benz Transmission pans like to rot around the drain plug as well on some models.
If your oil pan looks very rusted be sure to put something to catch oil if case you poke a hole right through.
8. A Loose or Damaged Drain Plug
The drain plug is located at the bottom of the oil pan and is used to drain the engine oil during an oil change.
If the drain plug is loose or damaged, it can cause BIG oil leaks.
It’s important to tighten the drain plug properly to prevent leaks. Always replace the drain plug gasket during an oil change to ensure a proper seal.
If you don’t change your own oil, be sure to hire a mechanic who doesn’t think an impact wrench is for tightening drain plugs.
9. Overfilled Oil Level
Overfilled oil levels can cause leaks.
If the engine is overfilled with oil, it can lead to excessive crankcase pressure in the engine, which can cause seals and gaskets to fail, resulting in leaks.
The adage more is better does not apply to vehicle fluids, keep the oil and all other levels in your car within the proper range and never overfill, you will do more harm than good overfilling stuff.
How to check your engine oil level
Starting with the car on a level surface and the engine cool, remove the dipstick and take a reading, if the level is far above the MAX mark you will need to have some oil drained off.
If you find the oil level is way over MAX I recommend having the level set properly and cleaning the oil present on the engine.
Then run the engine and re-check.
IF you are lucky the high oil level was the cause of your leaks, this is a rare event but it’s entirely possible if the engine oil is way overfilled.
10. Failed PCV Breather Components
Your engine uses a PCV breather system to recirculate crankcase vapor and allow the engine’s internal pressure to remain correct for optimal running.
The hot oil gives off vapors that flow through these components (which these days are mostly plastic.)
As oil vapor cools down it begins to condense and create carbon and oily sludge within the breather system.
Many times PCV hoses and or other components, such as breather plates and valves will begin to seep motor oil out of mating connections.
Rubber hoses will also begin to harden up and leak over time.
How to check for PCV issues
The first thing to check when it comes to your engine’s breather system is the actual running pressure in the crankcase when the engine is running. This is done with a CEM meter or other tool that can measure negitive pressure in millibars.
There should always be a slight vacuum within the crankcase when an engine is running.
Pressure, even slight, can cause leakage issues.
A pressurized crankcase indicates the breather valve or another component has failed and pressure is pushing outward on seals and gaskets, sending them to failure in extreme cases.
I will cover PCV diagnoses in much more depth in a future article.
How to Spot Engine Oil Leaks
Spotting engine oil leaks early on is crucial in preventing further costs to repair and even damage to the engine.
Regularly checking your oil level and for visible oil leaks under the car is a great place to start.
This can be as simple aschecking your oil and putting a piece of cardboard underneath your car at night to see where and if there are drips in the morning.
Monitoring the oil level on the dipstick is critical to knowing where the oil level is and whether it’s dropping fast.
And finally, pay attention to any unusual smells or smoke coming from the engine compartment while driving.
If you notice any of these signs, get it looked at to prevent further damage. Ignoring an oil leak for too long can lead to more severe engine problems and more costly repairs.
Oil Leak Clean-Up and Prevention Measures
If you have a big oil leak, it is important to clean up the spilled oil on your garage floor ASAP to prevent environmental contamination, slipping hazards, and staining.
To clean up an oil leak, you can use absorbent materials such as speedy dry, kitty litter, or oil-absorbent pads to soak up the spilled oil (if the leak is that bad.)
Grind the speedy dry, or kitty litter, into the floor with your foot to create a dusty, chalk-like effect on the floor.
Then simply sweep it up and use a good degreaser (such as simple green) to spray and scrub down the area.
Rinse it down and you’re all set.
Preventing Oil Leaks
To prevent oil leaks, regular maintenance is key.
This includes regularly checking the oil level and condition, replacing gaskets and seals as needed, and ensuring that all components are properly tightened during routine maintenance or repairs.
Additionally, using high-quality engine oil and following recommended oil change intervals can help prevent leaks from occurring in the first place.
Remember, old oil vapor hardens and eventually destroys gaskets, hoses, and seals.
Engine oil leaks can be a common problem for many car owners, but they should not be ignored.
Addressing engine oil leaks ASAP is crucial in preventing further damage to components and internal engine components.
