Unexplained engine oil loss

My 2001 Toyota Corolla has been losing oil sporatically for 2-3 years and i don’t know why. The engine has been meticulously maintained (oil/filter changed every 3000 miles). In the winter it loses 1 qt oil per 1000 miles driven. In the summer it loses approximately 0.25 qt oil per 1000 miles. The only sign of a problem can be observed during cold and winter months, when after starting the car, the engine makes a noticable knocking noise until it has been warmed up, at whcih point it goes away (typically after ~3 minutes). Note that the noise is only observed when applying the gas pedal, there is no knocking when at idle.

Any ideas?

A .25 quart consumption on a 9 year old car in the summeer is no big deal. The winter part of 1 qt/1000 miles puzzles me.

If you have seals or gaskets that are marginal and shrink in the winter, you could be using oil very gradually while driving and yet not notice any on the driveway or garage floor.

In any case check the PCV valve and any PCV filters located in the air clener, and make sure the distick is seated tightly.

You could try a high mileage oil which has sealants in it and see if it makes a difference. If it does you have weak seals.

There’s no mystery here. If there are no signs of the oil leaking out, then it is being burned. It’s either leaking past the rings or the valve stem seals and getting burned. The catalytic converters get rid of the smoke that you would see, for the most part.

For the knocking sound, you could try using 0W20 synthetic oil. Be warned that your oil consumption rate with probably be higher with that.


Where do you live-general area?
Do you warm up your engine during the cold season before driving off?
If you do, please describe in detail how you do it?

How many miles? Where do you live? How cold are those winter start-ups?

The noise could be piston slap, which quickly disappears as the engine warms up…

I live in Syracuse, NY. Annual snow fall = 110 inches.
I do not warm up the car for more than 10 seconds.

I want to assume that the rings are good, since I have maintained the vehicle very well (in my opinion). If the problem were the valve seals, is that an expensive fix?

Not really, but I’d wait till it got worse.

A 0W30 synthetic would make more sense than a 0W20 on a car of that age, as well as a block heater in the winter. It takes far more than 10 seconds for the oil to reach the valve gear on a cold day. Even with 0W30 oil, I would recommend at least 30 seconds before you take off. Drive gently for the first mile sif you can.

If you lift your foot off the gas pedal while going 30 mph or more, you may see blue smoke in the rear view mirror. That’s oil being sucked past the valve guide seal by the engine vacuum. A sure sign of new seals needed.

Please keep us posted on what you find out.

How many miles on the car? Well-maintained or not, higher miles means wear and you cannot assume the rings are good as you state. That’s what a compression and leakdown tests are for.

Even driving habits can play a part in this. If you do a lot short trips (2-5 miles, etc.) then it’s quite possible for oil control rings to sludge up even if the oil is changed ever 3k miles.

Sometime it’s too frustrating to stop oil leak if you don’t find the correct source of problem… Mine is concerned with the valve cover gaskets… Replaced from a car parts online shop… Work well by then…