If there’s oil leaking from your exhaust, think twice about driving your vehicle until you’ve fixed the issue. The cause may be something serious, so get it checked out. Here are some possibilities.
To begin with, the engine oil that comes out of a vehicle’s exhaust will show up as blue smoke: not black, not white – blue. If oil is literally dripping from the exhaust pipe, the engine will probably be running so bad you can barely drive the vehicle, anyway.
If there is oil coming out of your exhaust pipe, you might be dealing with bad valve stem seals, a damaged PCV system, or piston oil control ring problems.
Oil might also leak out of the exhaust when the turbocharger malfunctions. If the piston oil rings are clogged or no longer doing their job, you’ll have oil consumption and oil-related exhaust smoke as well.
Engine oil starts out in the crankcase oil pan, is picked up by the oil pump to pressurize the galleries and timing chain tensioners and VVT actuators, and splashes around as the crankcase spins and the timing components whirl and do their work. Some engines have small oil jets that spray oil on the underside of the piston to cool the piston head. The oil lubricates the cylinder walls but is squeegeed off by the oil control rings to keep most of it out of the combustion chamber.
Oil can leave the engine by leaking out onto the ground or by leaking past internal seals, o-rings, and yes, the oil control rings on pistons, all of which allow it to enter the combustion chamber. Oil can also be drawn out of the crankcase by a failing PCV system or past turbocharger turbine/impeller shaft seals, which also delivers oil to the combustion chambers.
Let’s take a closer look at some of the possible causes of oil coming out of exhaust:
Valve seals prevent the engine oil from entering the combustion chamber, particularly from the intake valve stem seals due to the low pressure in the intake stream. There is at least one intake valve and seal per cylinder, sometimes two. Exhaust valves have seals too, but since the exhaust has pressure at the bottom of the valve stem and not vacuum, exhaust valve stem seals aren’t as leak-prone.
If your vehicle smokes after it idles for a while or if it makes a large blue cloud right after you start the vehicle in the morning or after spending an hour shopping, the valve stem seals are typically the reason. But valve stem seal leaks aren’t as noticeable while driving and don’t typically allow enough oil to pass so that it drips out of the tailpipe.
When these valve seals fail, oil can leak into the combustion chamber and burn. The fluid could also leak out of a vehicle’s exhaust pipe.
This is a diesel piston but the same rules apply on gas burners. The oil control ring is built to be a “scraper” or squeegee that cleans most of the oil off the cylinder walls (it can’t get all the oil, but it’s not supposed to), so that there’s enough to lubricate the compression rings but not so much that the oil mixes in great amount with the combustion mix.
If the oil scraper rings become compromised by carbon or if the cylinder walls become damaged somehow, oil will be left on the cylinder wall and will be consumed in the combustion chambers and then make its way out the back. Piston damage can also cause crankcase oil to enter the combustion chamber.
The head gasket seals around each combustion chamber and the coolant passages (see photo) that pass from the block into the cylinder head, but has very little to do with the engine oil except on overhead cam engines, where a pressurized oil feed is fed to the camshaft journals and lash adjusters.
That being said, the oil passage, when it leaks, practically never sends oil to the combustion chamber, so that cylinder head gasket is barely worth mentioning when it comes to oil dripping from the tailpipe. Look somewhere else for the problem.
Yes, you can, but it’s best no to. If you drive while there’s oil in the exhaust, you can cause significant damage to your vehicle’s engine. While most damage is reversible, the engine can sustain severe damage if you end up running it completely out of oil and welding everything together or start it knocking.
On the other hand, some drivers motor for tens of thousands of miles on smoking engines without a care in the world. Of course it pollutes and causes issues for other drivers, and you don’t want to do that.
The best next step after spotting the oil leak is to get your vehicle diagnosed by a mechanic as soon as possible to single out potential causes. Correct these problems as soon as you can.
Driving with oil in your exhaust can also lead to other complications, such as disruptive engine noise, knocking, and engine seizing.
Some ways to prevent oil from coming out of the exhaust are to clean your PCV valve, repair or replace faulty engine components, and perform maintenance on your vehicle at least once every six months.
As mentioned earlier, a bad PCV system causes pressure to build up in the crankcase. Cleaning the PCV valve regularly can prevent the accumulation of gunk and dirt that prevents gases from being redirected. When gases can flow freely, pressure in the crankcase reduces.
If your vehicle’s turbocharger becomes inoperative, it’s important to get it repaired or replaced as soon as possible. A bad turbocharger compromises a vehicle’s ability to run. Not only does its fuel efficiency reduce, but its oil pressure also increases exponentially.
Having a professional inspect your vehicle at least twice a year is a great way to prevent issues. A mechanic can diagnose your engine and either repair or replace faulty parts, potentially preventing oil from coming out of the exhaust.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.