Oil Burner May Have Worn-Out Valves
Question: I have a 1972 Toyota Landcruiser with 45,000 miles on it. It burns oil and five of the six spark plugs are oil fouled. In a compression test, all the cylinders were OK. Is it possible for oil to pass by the rings and still have good compression?--D.I.
Answer: It is entirely possible for an engine to burn oil even when the compression in the cylinders is up to manufacturer specifications.
Pistons are sealed against cylinder walls by metallic rings. Most engines have three compression rings and one oil-control ring. The compression rings keep explosive forces inside the engine’s combustion chamber.
The oil-control ring prevents excess oil from coating the cylinder walls and burning up during the piston’s down stroke. So, the oil-control ring acts like a squeegee. If it becomes clogged with sludge, it will not operate properly, but the three compression rings will continue to do their job.
You must be careful in your diagnosis, however, because it is more likely that the oil is entering the combustion chamber through worn-out valve seals or valve guides. It’s unusual to have five bad oil-control rings. You can easily check the valves by pulling off the valve cover. Of course, inspecting the rings requires tearing apart the entire engine.
Q: I own a 1983 Honda Accord. At 45,000 miles, I had a front brake job that included turning the rotors. By 60,000 miles, my steering wheel began to vibrate during hard braking. The brake pads haven’t worn out. What’s the problem?--A.R.
A: The front disc brakes on Honda Accords are susceptible to such problems. The rotors must rotate perfectly true. If there is any wobble, they tend to cause uneven wear on the pads, which then further causes uneven wear on the rotors.
The uneven wear then results in a vibration when the brake pads hit the rotor. In most cases, the vibration is an annoyance that should not affect brake performance. But if the vibration is severe, or if there is any side pull, you should attend to the problem.
Some Honda dealers have a special tool that enables mechanics to turn the rotors while they are still on the car. That’s supposed to result in zero run-out.
It’s possible that the repair garage or dealer that performed your brake job did not have this special tool. Or it’s possible that the special tool, if used, has not really solved the problem.
Q: My problem is with my 6-month-old 1985 Volkswagen GTI. It diesels. The dealer put on a new fuel pump, but the problem continued. Will I have to go from dealer to dealer to find the cause or can you help my wheels?--B.P.
A: Dieseling, also known as run-on, occurs when a car continues running after the ignition is turned off. It’s not caused by a faulty fuel pump, however.
When an engine diesels, the spark plug is usually so hot that it ignites the fuel without an electrical spark. Modern engines run lean and hot, which contributes to the problem. Also, gasoline is growing more volatile, requiring a lower temperature to ignite.
There are usually three causes of dieseling: too high an idle speed, incorrect spark plug temperature range or carbon buildup in the cylinders. Check the plugs and idle speed. You may also have better luck with a different brand of gasoline. It’s unlikely that you have carbon buildup on a 6-month-old car.
