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Mysterious odour could be stale gas


QUESTION: I'm the original owner of a '92 5.0-litre Mustang with about 100,000 kilometres on it. The car is driven maybe 300 kilometres a year. Immediately after start-up and all the while it's driven, there is an odour of varnish or wood alcohol all around the car and not necessarily from the tailpipes. It's not the rotten-egg smell from a catalytic converter. Should I be driving the vehicle more and putting in fresh gas more often? Are there any fuel additives I should be using? I've heard the term "sour gas" but I'm not sure what that is.


A: The most common automotive source of a varnish-like odour is stale gasoline.

As gas ages, some of the hydrocarbon molecules oxidize, creating a lacquer or varnish-like residue. Remove the fuel-filler cap and take a careful, small whiff. If you smell that bitter, sour odour, it's the gas.

If you can't drain and flush the tank, change the fuel filter, add Sea Foam Motor Treatment to the gas and run the tank as near empty as possible, then fill up with fresh gas - non-oxygenated if it's available - and more Sea Foam.

Also, make sure the evaporative emissions system and charcoal canister are working properly and not leaking any fuel vapours.

Q: I recently purchased a 2010 Mercedes ML 350 with a V-6 engine. The manual says it requires premium gas - 91 octane or higher. What are the consequences of using regular gas occasionally, given the price difference?


A: All I can tell you is that I've never had an issue operating my BMWs and VWs that "require" premium on 89-90 mid-octane gas.

Q: I have a 1972 Sea Ray boat with a four-cylinder GM engine, basically the one GM used in the Chevy II. While winterizing the boat, I started spraying fogging oil into the cylinders and when I looked up, the red plastic straw was gone. I assume it blew into the cylinder and have tried lots of things to fish it out. I've tried a bent wire with many different bends, and angled tweezers, rotating the cylinder to top dead centre in the hope it would bow out and I could grab it. I even used a vacuum cleaner nozzle in the hope that the suction would rotate the straw around so I could at least see it.

I've had several people tell me to just fire it up because that small a piece of plastic would get hot and vapourize. I'm reluctant to do this, fearing that the plastic will melt and either gum up the cylinder wall or rings or stay melted on the edge of a valve and hang it up.

I suppose the safe thing to do would be to take off the cylinder head, but I want to avoid all that work if possible. Of course, if I fire it up and hang up a valve, I would end up taking it off anyway. What is your opinion of firing it up and hoping the plastic would vapourize without creating any damage?


A: First off, you have no absolute proof the nozzle went through the spark plug hole and into the cylinder. The fact that you were not able to see, feel or remove anything with the piston at top dead centre lends credence to this possibility. Wouldn't you be, ah, angry if you were to pull off the cylinder head and find nothing?

In my journalistic efforts at due diligence and accuracy, I went out to the garage, picked up a red nozzle from an aerosol can and put it to the test. With a simple wooden match, it caught fire and, with the flame removed, continued to burn. The only residue was a light flaky ash.

If it were mine, I'd just fire it up. The plastic will liquefy, burn and vaporize in the 1,600-degree combustion heat.

Paul Brand, author of "How to Repair Your Car," is an automotive troubleshooter, driving instructor and former race-car driver. Readers may write to him at: Star Tribune, 425 Portland Ave. S., Minneapolis, Minn. 55488 or via email at [email protected]. Please explain the problem in detail and include a daytime phone number. Because of the volume of mail, he cannot provide personal replies.