Octane-Boosting Remedy Can Hurt Engine

Question: I was told that by adding up to eight ounces of denatured alcohol to my gasoline, I could raise the octane rating enough to quiet the ping on my 1969 V-8 engine. What trouble might I experience if I use this additive?--R.M.B.

Answer: Major automobile manufacturers strongly advise against such a practice, although it will indeed raise the octane of your gasoline. On older engines, including yours, the addition of alcohol can reduce the protection provided to the engine by lead in the gasoline. Because the amount of lead in gasoline has already been sharply reduced in light of federal environmental regulations, you would run an even greater risk of engine damage.

On newer cars, alcohol can cause serious problems with fuel-injection systems. Your 1969 V-8 engine almost certainly has a carburetor, but many newer cars are equipped with fuel-injection systems that can become fouled and plugged because of alcohol.

Because too much spark advance can cause ping, your problem can be dealt with more effectively and possibly more economically if you make sure the engine is properly timed.

The most likely cause of ping, as you correctly assumed, is need for higher-octane fuel. If you are unable to purchase high-octane leaded gasoline, you can mix high-octane unleaded with regular leaded. Or you can purchase high-octane unleaded and put in an additive, available at most auto parts stores, that will simulate the function of lead.

Finally, many older engines develop carbon deposits inside their cylinders, especially if the car is not ever driven at freeway speeds. The deposits tend to reduce the volume of the cylinders and raise the compression ratios of the engine. That can cause ping that is very difficult to eliminate. An occasional drive on the freeway will help keep the engine clean.

Q: What causes the smell of raw gas inside my 1978 Lincoln Town Car on hot days? I have had the engine analyzed several times, and a specialist has examined the carburetor. There are no leaks and other problems have been corrected, but still the sickening fumes of raw gas are in the car.--J.J.V.

A: Sometimes specialists look for complicated answers to simple problems. The fuel filler neck is in a recessed area, which has a vent tube that allows spilled gas to drain down to the ground.

If this tube is plugged, gasoline will remain lodged inside the small compartment, work its way into the trunk and then permeate the car. Pour a small amount of water into the tube and check under the car to see that it is properly draining.

Another possibility is that the carbon canister inside the engine needs to be replaced. The service interval on the canister is 60,000 miles, but it can become soaked with gasoline before then and cause odors.

The simplest cause of your problem would be that you are relentlessly topping off the gas tank at the service station. Car manufacturers design a small air pocket in gasoline tanks to allow room for fuel expansion on hot days. By topping off the tank, you can fill this air pocket and defeat its purpose.

Q: I had the waxy window film you discussed in one of your columns. I used vinegar, window cleaner, ammonia and paint thinner, to no avail. What finally worked was commercial windshield washer fluid. I hope this will be of help to others.--C.W.

A: The washer fluid--available at discount and auto parts-stores--contains alcohol, which is another good window-cleaning agent. Use care with a lot of these fluids because they can damage your paint.