Why do Cars Burn Oil?

Ever wonder where your car's engine oil disappears to? If its not leaking oil, its burning it! In this video, the two main reasons why internal combustion engines burn oil are presented and discussed.

The piston crank bearing, connecting rod wrist pin, cylinder walls and valve train are all coated with oil through the engine's lubrication system. Learn more on that in my engine lubrication system video here:

The first reason cars burn oil is because of worn piston rings, a stuck oil control ring, or clogged piston head. This can likely be attributed to carbon and sludge buildup blocking the oil return holes drilled into the piston head. Sludge and carbon builds up when the petroleum in the engine oil breaks down at high temperature - an engine design defect. The oil has no where to drain, and gets drawn onto the combustion side of the piston where its burned and exits the exhaust.

The second reason cars burn oil is through the valve stem seals. The valves are situated between the well-lubricated cylinder head and combustion chamber down below. When the valve stem seals age, they get dry and crack and may leak oil. Typically overnight, oil pools up around the valve and drips down on to the piston. The next morning upon startup, a huge plume of blue smoke is sighted out of the tail pipe, which is the oil burning away.

Some engines are more susceptible to oil burning than others. The only way to cure oil burning past the rings are to drill holes in the piston heads and change the rings, which requires a full engine tear down. Changing the valve stem seals are still labor intensive, as it requires removal of the engine head and valves.

Here's how an engine works, with disassembly:

The engine components demonstrated in this video came out of a 2001 Toyota Corolla. It had 204,000 km and burned some oil through the piston rings. The piston ring problem is common on the Corolla, Camry, Rav4, Scion tC, Matrix and Highlander with the 1ZZ-FE and 2AZ-FE engines.

Here's an excellent video on rebuilding the 1ZZ-FE engine:

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[roycai]

nice video, please remember to return the toothbrush and sock to your brother.

[danielginther]

From my experience, oil always produces a white smoke whereas excess fuel produces bluish/black smoke. I enjoy all of your videos and think you do a great job!

[seankim]

I wondered why my 2002 Camry kept burning oil. I was told about the possible piston ring situation. Now I see it. Thanks for the enlightenment.

[michaeldeguzman]

you must really love your brother. great video.

[lazalm]

Correct me if I'm wrong, but the oil flows the other way around. The oil travels from the crankshaft through the hole in the Connecting Rod Bearing. Then there are passages in the Connecting Rod that go up to the Piston Pin and also to the Oil Jets on both sides of the Connecting Rod. The Oil Jet squirt oil upwards to the underside of Piston which then drips to the holes of the Oil Control Ring. The middle Oil Control Ring stores the oil lubricating the Cylinder Walls and then the top & bottom Oil Control Ring will scrape the oil off the Cylinder Walls.

[wholeNwon]

I knew about all that but never actually saw the oil control ring taken apart. Thanks. Your videos are always worth watching.

[simple-]

My G35 has this issue. Can't afford a new engine right now and currently burning 5 qts of oil every two weeks... getting worse. Good informative video👍

[quinnydanny]

Thanks for the easy comprehensive explanation of why I keep dumping gallons a week in my car. And I just thought it might have been a pcv valve ( hoping for an easy fix ) now I gotta start looking for another car

[chocolate_squiggle]

All the videos I ever watched trying to learn how engines worked, no-one ever showed the rings in as much detail as you did in these couple mins just now. They just say they're to stop oil and then slot them in during their rebuilds. I can see much better now how they compress a bit, why they don't damage the cylinder walls, how the oil actually drains (I thought it all just got scraped down the cylinder wall), etc. It's just a nice level of detail for us guys who've read some basics but never had the chance to see these things up close. Like I said in another comment, you're making this stuff so much more accessible. I never pulled cars apart because it all seemed too confusing & beyond my abilities - grainy black and white pictures in Haynes manuals often confused me more than they helped. I'm sure with your videos you're showing kids they needn't fear fixing their own cars mate. Your a fantastic human sharing all this.

[RockabillyRambler]

Doing the lords work. educating people.







Morgan freeman is looking down on you aprovingly.

[JMRSplatt]

Quick story.. Last year in 2021, I bought a 2006 Honda Accord 2.4L/5-speed/Coupe/EX-L with 155k miles. I was not DIYing my oil or anything at the time. Having purchased the car from a mechanic, I didn't check the oil for a couple weeks, and when I did it was BONE dry, just a drop maybe. After putting in enough oil and checking, I realized it was burning a ton of oil. I think it was burning over 1 QUART PER 1k miles, maybe more! I went through a 5 quart bottle quite quickly. I also noticed black sticky residue on the tailpipe tip, but not really much smoking that I could see.

This put me into a bit of a panic and swapped my current research and hobbies over to car DIY; researching, reading, buying repair manuals, etc. I've come across this piston ring information several times on YouTube and Accord forums. At first, and being a newbie, I thought maybe this 'AT-205 reseal', MMO, or some sort of additive. But AT-205 is for rubbers, not metal rings, I kept reading and watching random videos. In the meantime, I changed and added oil as needed. I used SuperTech and Mobile 1, but mostly SuperTech once realizing they are basically the same oil. I changed it as soon as possible, then at 2500, 3000, 4000, and now 3k-5k miles. I've put on 20, 000 miles already.

Forward in time about 5 months and the oil consumption has slowed to a crawl! It used about 1.5 quarts over the last 5000 miles! I'm guessing the car had sat around before being sold(some other clues were there also), with old oil, and it GUNKED up the rings. However I think the frequent changes have cleaned them out! I was looking at some condensation coming from the tailpipe last week and also noticed that the nasty GUNK that was built up, it is nearly all GONE!?! huh?! I wanted to clean it off to see what the new build up would be, but it's gone! I've also added a quart of Marvel's Mystery sparsely, mostly in the oil, a bit in the gas. That also seems to have helped; today's oil change was less black and much less was burned off.

It's puzzling to me why someone would sell such a good car. Sure it has some other minor issues, a small water leak, and a bit of the headliner is just starting to separate, but man it's a great personal car, peppy, comfy... and I'm not looking forward to all electronic everything of the new cars.

Thanks for the videos; your teardowns and explanations have been well worth my time!

Edit - a couple things and added clarification without altering content

[EnemyAlreadtIntheGates]

I was able to replace an 02 Camry's valve stem seals with the head intact. It can be done by removing the cams, rotating the piston about to be serviced into TDC and blowing compressed air into the combustion chamber. Remove and reinstall the valve keeper and seals one at a time on the cylinder that is pressurized.

[markchimmy]

Great video and explanation!
People don't put cheap oil in your car and change your oil on time! And you should never have this problem!

[hamzaraissouli]

Gotta be careful using someone's sock. You don't know what they used it for. Great material btw. I had to replace my Toyota Yaris engine a month ago. The engine used to consume 3 Liters of oil each week in its last days. Now it all makes sense

[winstonleighton]

Marc Hauser, Actually older vehicles require thicker oil to fill those worn out specs due to aging. My 20 years old Honda was labelled as for 10/30 grade . I have switch to a higher grade

[snider]

That was honestly the best video on these Toyota engines that is burning excessive amount of oil I have ever seen very informative very good job

[punityaduvanshi]

I am from india and a lawyer.... but i have passion for cars and engine...i love ur videos...keep it up...

[jacknobles]

I would think the oil control ring would leave a very thin layer of oil on cylinder walls for lubrication of the compression rings? If there were no oil for the compression rings the rings would wear out very quickly. So, with that in mind, by nature of design, even a brand new engine will burn / consume a certain amount of oil. BTW, I have a 1996 Isuzu Rodeo with 3.2 V6 engine that has now begun consuming oil via the valve guide seals after 472, 000 miles. The engine still runs fairly well but I decided to completely rebuild the engine as the Rodeo itself is cosmetically in great condition. Thanks for posting this video!

[abdulazeez.]

4:41 "you wake up in the morning and brush your teeth" that's hilarious 😂😂

[MichaelCzajka]

Ethanol fuels are one of the major culprits in causing sticky rings. Ethanol oxidises to form aldehydes which then polymerise to form a sticky sludge that takes ages to remove.

The sticky rings allow fuel into the sump and which thins the oil and reduces lubrication.

This loss of lubrication results in piston and bore scoring even in low-mileage cars.

🙂