I am not a native-speaker so bare with m English.

Two months ago, I bought a 1999 corolla (80K miles). After four highway trips, I found that the engine oil was all gone at 800-mile point and the engine light was flashing. I had to add 3 quarts of oil to fill it up. The car run very smooth, engine was quiet before the oil pressure dropped very very low. It has great gas mileage (34 mpg on highway with AC on all the time). I did see some black residue on the bumper over the exhaust.

So I took it to a garage, the guy steam cleaned the engine, replaced PCV valve, spark plugs and service the throttle body. He said the oil pan gasket and valve cover gasket were leaking ($440 repair cost), but the leak was not severe and could not be the only reason for the excessive oil consumption. Then I took it to anther garage, the mechanic checked engine and found that there was some oil leaking, but not so much. He checked the exhaust smoke and it was normal. He said if the engine is burning oil, it must be in pretty bad condition and car could not have such good gas mileage.

I took my car back and drove at local for 300 miles, the oil level remained full. I then drove 200 miles on the highway and you know what, 1 quart of oil was used. Again the car runs smooth and quiet, but when I went uphill at over 55 mph, I could hear some noise from the front. I took the car to the second mechanic again, he could not tell why.

So what’s wrong with my car? Do I need to rebuild the engine or just trade in the car? Is my engine burning oil? How can I tell for sure?

Any suggestions are greatly appreciated.

At 80k, it should not be burning oil. The fact that the oil burn off only happens at freeway speeds makes me think the engine is not warn out.
I would pull the plugs. Burning oil at that rate, would create a huge oil buildup on the plugs. If the plugs are clean, then you are leaking the oil out.

Thanks for your suggestions. Yeah, actually the guy checked the spark plugs after I drove the car for 500 miles. the plugs are very clean.

Hello,

You have narrow in the problem and eliminated that high consumption is not due to intrusion of oil into the bores and cylinders. It did not show oil is burned when you opened the plugs as no heavy soot deposits were found.

Then you have to pinpoint the possible passage of oil to leak. By doing so, before entering your garage to park overnight, place a cardboard or carton box matting underneath the engine. In the morning, check the spot where oil dripped so you can trace the origin of the leak. Once you have pinpointed, start looking around. By the way, the spot where the oil leaked may not tell you exactly where the oil came from due to many factors. If nothing is visible while looking at the engine, inspect closely the following: after the oil pan gaskets, check the crankshaft pulley, the oil seal could be damaged. Or at the mounting of the engine block and transmission bell housing, if oil is present, then there could be a leak on the crankshaft oil seal inside the transmission housing. Or at the neck and bases of the oil dip stick tube, at the camshaft pulley or distributor. These areas that I identified are likely the joints where oil could possibly leak. Of course changing oil seals may involve expensive work but you need not have to rebuild or replace the engine.

Good luck.