Keeps On Ticking After Key Is Off
Question: I have a 1982 Oldsmobile Cutlass with an eight-cylinder engine. When I turn off the motor, it keeps on running. How can I correct this problem?--S.N.
Answer: The problem you describe is known as run-on or dieseling, so-called because the engine continues to run like a diesel even though the spark plug ignition circuits have been shut down.
How can an engine run without a spark? The engine continues to draw fuel and air through the carburetor, which typically has a reserve of fuel in the something called a float chamber. Fuel injected engines will not diesel.
The gasoline is ignited inside the engine by residual heat, either on the spark plug itself or from a hot spot on the cylinder walls or cylinder head.
Dieseling is often caused by the idle speed of the engine being set too high. But dieseling exacerbated during hot weather.
Gasoline has a higher tendency to vaporize and a higher tendency to knock in hot weather. It means you are more likely to have uncontrolled combustion inside the engine and greater fuel problems like flooding in hot weather.
To compensate, gasoline refiners reduce volatility during the spring and reduce it further during the summer. But this adjustment is rather crude. If a sudden heat wave occurs, it is easy for gasoline to become too volatile.
In addition, your engine runs hotter in hot weather, so hot spots inside the engine are hotter and the tip of the spark plug is hotter, as well.
In older cars such as your Oldsmobile, carbon buildup inside the cylinder over the years can raise the compression ratio, which promotes dieseling. Carbon deposits also create hot spots by insulating small spots in the cylinder.
The solution to your dieseling problem is relatively simple. You should make sure that the idle speed is correctly set. Try different brands of gasoline that may have different levels of volatility. And you might want to use a gasoline additive that promises to remove carbon deposits. Techron, an additive used in Chevron products, seems like an effective product in removing carbon.
If after all of this, the car still diesels on occasion and mechanics can not fix it, you might want to use a simple procedure to stop it. When you shut off the car, keep the car in drive. The additional load from the transmission will almost certainly kill the engine. Then put the car in park.
Q: I have had numerous friends and relatives tell me how to break in a new car. I’m planning on buying a new Honda Civic. What is the best way to break it in?--B.H.
A: The most important step is to carefully read the owner’s manual and follow the manufacturer’s recommendations. Forget all the advice of friends and relatives, who may be thinking of what was correct in the 1950s.
Break-in occurs as new moving parts inside the engine, drive train and suspension undergo their first usage. Inconsistencies in metal parts, such as burrs or surface roughness wear down. Rotating machinery under great stress, such as the piston rings and crankshaft bearings, must seat themselves in their permanent positions.
The break-in periods of cars today are much less than years ago. Engines and suspension parts are more precisely machined and require less time to properly seat themselves.
The normal break in periods are now around 1,000 miles and the restrictions during that period include no wide open throttle acceleration and no high-speed driving. Some manufacturers also put special additives in the oil for break-in, so follow recommendations and don’t change the oil too soon.
