Question: My 1984 Volkswagen Quantum has a waxy film on the glass that's impossible to remove. I have tried kitchen cleanser, razor blades and soap. What's the solution?--V.M.
Answer: It's probably not vinyl gas, which is bled off from new vinyl and easily washed off with soap and water. Something else must have gotten onto the glass.
Do not use anything abrasive because you will scratch the glass and ruin the windshield. I suggest you try vinegar or ammonia, the two best glass cleaners.
If those don't work, an auto-glass shop may be able to remove the film with a glass rouge abrasive.
Q: I have a 1980 Firebird that starts fine when it is cold. But when it's warm and I shut off the engine, even for 10 minutes, it hardly turns over when I try to restart it. I have to wait awhile and then it will turn over and start. Can you give me any advice?--J.R.
A: Your problem is a common one, and it gets worse in the summer months, as you have discovered. A hot engine is more difficult to start for several reasons.
After you turn off your engine, the temperature under the hood continues to rise, because the heat coming off the engine block and has nowhere to go.
As the temperature goes up, electrical resistance in the large amperage cables, which carry electrical current to the starter motor, goes up. That robs the starter of power, especially if the cable connections are dirty.
In addition, the tolerances between moving parts inside the engine close up when they get hot, so there is more engine friction when you try to start.
You should have your mechanic check the battery to make sure it is delivering the voltage and current the starter needs. You should also make sure the large electrical cables are in good condition and their connections are clean.
If all this doesn't solve the problem, you possibly have a faulty starter motor. It may have partially worn out brushes that aren't delivering the required power in a high-load situation.
Q: My 1977 Volkswagen Rabbit with 41,700 miles on it has high oil consumption. I replaced the valve-stem seals, but that made the problem more acute. Oil consumption is one quart every 600 miles. Only minor oil leakage is occurring. An engine compression and leak-down test showed three of the cylinders at 90/90 and one at 90/80. Please explain what the problem is.--N.S.
A: So far, your detective work has been right. Oil consumption of more than one quart per thousand miles is considered excessive for your car. But you need to re-interpret the leak-down tests.
A leak-down test is often done to supplement the diagnostic information from a compression test, which measures pressure generated inside a cylinder by the pumping action of the piston.
A leak-down test is a little more sophisticated, because it can show whether poor compression is due to valve-stem wear or piston-ring wear. A mechanic screws an instrumented pressure hose into the spark plug hole. He pressurizes the cylinder and then takes a reading of the amount of pressure the cylinder will retain.
Then, he squirts oil into the cylinder and conducts the test again. If the pressure leakage is significantly less with the oil, the piston rings are suspect. If not, then the valve stem may be leaking.
Your readings indicate that you have at least a 10% leakage situation, which is excessive. The 90/80 reading is especially out of specification. The spark plugs should be checked for oil fouling.