Question: I have a Ford equipped with a 400-cubic-inch engine that has a problem with the oil-pressure warning light coming on when the car is idling. Another person who has the same problem with his Ford said the problem is in the oil pump. He advised me to drain the engine oil and run diesel fuel in the crankcase for a few minutes. I think I'll try it at my next oil change.----E.L.L.
Answer: If you do, there's a good chance you'll be out shopping for a new car the same day. Washing an old engine with diesel fuel is an old idea that should have been forgotten years ago.
An old engine develops deposits of gunk and tar inside its crankcase. By disrupting and dislodging those deposits, you run the risk of clogging the lubrication system and ruining the engine. Good-quality oil already has detergent in it to keep the engine clean.
The problem with the oil warning light has several other possible remedies you should consider before doing something that you'll later regret.
You should check whether you have a faulty engine sensor. A mechanic can use a gauge to measure the actual oil pressure. If it is low, your engine may be idling too low. Switching to a heavier-weight oil may help as well. And if you do have a faulty oil pump, it will be a lot cheaper to fix it than to replace the engine.
Q: We have a 1983 Sentra with a manual transmission. Ever since we got it, it bucks or bumps or jerks when you lift your foot off the accelerator. We were told it is normal with a front-wheel drive. It is so pronounced that it would seem harmful to the car, but after 30,000 miles, the car seems fine. Is there a problem?----T.L.
A: The bucking problem you describe is typical on many newer cars, especially those with stick shifts. The bucking occurs when you abruptly depress and lift the accelerator pedal.
The Sentra is equipped with an electronically controlled fuel cutoff valve, which kicks on when you lift your foot off the accelerator. It's designed to improve fuel efficiency by cutting all power as soon as you lift your foot. In the old days, an engine would spool down more gradually.
The problem is compounded when you lift your foot off the accelerator and then quickly depress it again. The fuel cutoff valve first cuts off fuel and leaves a small vacuum in the intake manifold. It then takes a second for the engine to get gas when you quickly change from deceleration to acceleration, creating what is called a "lean stumble."
The only remedy is to accelerate and decelerate more gently at slow speeds.
Q: My 1980 Toyota Celica had two blown head gaskets within 35,000 miles. The manufacturer says this is "normal wear and tear." Can this be?----J.A.
A: If it is normal, Toyota must be doing a huge business in supplying replacement head gaskets. If the second gasket had been properly installed, it should have far outlasted 35,000 miles.
It's possible that two different problems in the engine block or head caused the two gaskets to blow out. Since you don't describe any of the circumstances, it's difficult to say what happened. Possibly, a gasket with the wrong thickness was put in or it was not properly installed.
Ralph Vartabedian cannot answer mail personally but will respond in this column to automotive questions of general interest. Do not telephone. Write to Your Wheels, You section, The Times, Times Mirror Square, Los Angeles 90053.