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Oil burning problem

80000 miles…car burns oil as much as 3 quarts two months or less…no smoke no leakage when oil is low…car runs great…mechanics are stumped too

The problem is most likely leaking/weak valve seals. To compound the problem the oil drain holes in the engine head may be stopped up. When this happens oil pools around the valve seals and even more oil is burned. You don’t see the smoke but drivers behind you can. The mechanic who changes out the valve seals can clear the oil drain hole obstructions. Your Prizm is made by Chevrolet.

valve covers were changed recently but I will ask my mechanic if he cleaned out the drain holes…thank u…hopefully this will be the answer…we have been fighting this problem for over a year and a half

The Prizm was a rebadged Toyota Corolla. It was made by Toyota and sold by General Motors under the Chevrolet name. I would agree that the likely cause is sludging of the oil passages in the cylinder head, allowing oil to accumulate and leak past the valve seals and be burned. Any good shop should be able to perform this repair, just as long as it hasn’t been run out of oil enough times to cause more extensive damage to the engine.

Did these mechanics even bother to run a compression and/or leakdown test?
That test should be Step One even though that test is not 100% definitive.

Oil typically gets burned in a few different ways.

As Missileman suggested, oil that lubes the valvetrain can pass by worn out valve stem seals and be drawn into the engine whenever cylinder vacuum is high, which is when you decelerate. If these seals are worn it can also pool on the backs of the valves (in cylinders where the valves are stopped in the open position) and burn off when you next start the engine. Generally in these cases you’ll see a puff of grey in the morning, but you won’t see it as you drive unless it’s really bad because it’s dissipating behind you. Those following you will see it.

The second way it can burn is if the cylinders are worn out and/or the rings tired (lost their spring tension). That’ll smoke on acceleration rather than deceleration. As with the other, you won’t see it but the cars following you will.

Oil rings, the rings that wipe the cylinder walls down, can also get gummed up, especially if you’re not religious about yuor scheduled oil changes. That can allow excess oil to get burned.

I’d start with a compression test to find out how worn the cylinders are.

Note that although your mileage is low, 10,000 miles a year indicates a lot of in-town driving. That can wear an engine out in far fewer miles than highway driving.

You beat me. I need to learn to be more succinct.

How many MILES does it take to burn one quart of oil??

Good question. If the OP is the original owner, he’s driving an average of 10,000 miles per year and using 18 quarts. I make that to be a quart every 555 miles.

But I’ve had to make some assumptions to get there. My assumptions may be incorrect.

Without any smoke showing, I’d say that you’ve got coked rings. You report no loss of power or other driving anomalies (fouled plugs, etc). I’d have the PCV valve (however it’s configured on your engine) changed (cheap), and I’d also highly recommend Auto-Rx (www.auto-rx.com).

Good luck!