Questions and Answers

Oil Burning Lexus

Q. I recently purchased a 1994 Lexus SC 300. It had 68,000 when I purchased it (May 1, 2000) I have since put 10,000 miles on it, and have changed the oil 3 times. I have discovered that it is burning oil ( I can't detect any leaks or smells of oil burning as a result of leaking on the under carriage ). It burns about 2 qts every 1000 miles. It had a single owner, who leased it, purchased it at the end of the lease, kept it for a year, then sold it. I ran the engine number through one of those services to make sure it was ok and it came up with the correct mileage, no damage, etc. It is a manual shift, and appears to have all of the standard equipment. I'm afraid to bring it to a dealer without checking in with someone such as yourself. What are the possible reasons why the car is burning oil? I drive about 125 miles a day. I also, do not have records of the maintenance of the car. I did take it to a mechanic to check it out prior to purchasing it. Also, Can you give me an idea, of what I can expect to pay for the repairs? Thanks for your help.

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Thanks, Roberta

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Burning two quarts of oil in 1,000 miles would not be really noticeable by smell, it would only be detected by the dipstick. Since there is only one place the oil can be burnt, in the cylinder, the question is: How is it getting in there? Since it is not a turbcharged engine that leaves two possibilities. Up past the rings or down through the valves or a combination of both.

If it is coming through the valves, the valve seals will need to be replaced. This can be a fairly simple repair, but it does require some expertise to do. Most shops can do this quite easily although it is a labor intensive job. While the seals themselves are cheap enough, the labor could run about $250.00 to $300.00.

If it is coming up past the rings, then we have a problem. Replace the piston rings require a lot more work involving major engine disassembly. The oil pan, cylinder heads and the piston/connecting rods have to come out. Also the connecting rod bearings should be replaced at the same time. This job could run about $1500.00.

A wet and dry compression test can point you in the right direction. First the compression is tested and the results noted. This is the "dry" portion of the test. Then a couple of squirts of motor oil are put into the cylinders and the compression test taken again. This is the "wet" portion of the test. The oil will temporarily seal the rings to the cylinder wall. By comparing the dry and wet readings, it can be determined if the rings are bad or the valves. If the wet readings are about 20% higher than the dry readings, you have weak rings. If the readings are basically the same, then it's the valve seals.

On a relatively low milage engine like this, I would say there is a very good chance the seals are leaking and not the rings.