Dear Tom and Ray:

I have a 5-gallon gas can that has an old-style spout, which used to have a bright-yellow cap. The cap got lost, so I got a rubber stopper to put in the end, to prevent vapors from escaping when not in use. Well, last night I put some gas in the car from this can, and not thinking, I forgot to take off the rubber stopper.

You guessed it, the gas did not pour, but with a little shake, it started to flow, and a lightning bolt hit me: "Oh *#!! -- the stopper fell in the gas tank!" My question is, What to do now? Will the stopper dissolve and mess up the fuel injection? How long would that take? Could the stopper roll around and block off fuel to the pump?

-- Bob

TOM: You can go back to sleeping at night, Bob. I doubt the stopper's going to hurt anything.

RAY: One of two things will happen. Either that stopper will just sit at the bottom of the gas tank forever, never bothering anybody, or it will slowly disintegrate.

TOM: Some types of rubber, like neoprene, can stand up to petroleum products. Some can't. I have no idea what the chemical makeup of your stopper is. If it was a stopper designed for a gas can, I'm sure it'll just be an innocuous, permanent resident of your tank. Whereas if you pulled it out of a bottle of Baboon Thigh Pinot Grigio, it might break down over time. But I still doubt it's going to cause any problems further upstream.

RAY: Even if the stopper disintegrates slowly and gradually dissolves in the gasoline, the small number of dissolved rubber molecules in any given tankful of gas probably will just combust in the engine, along with the gasoline, and never be noticed.

TOM: And if the stopper dissolves into small rubber bits (which probably is more likely), and those pieces sink to the bottom of the tank, they'll be prevented from entering the fuel line by the "sock" filter on the bottom of the fuel pump.

RAY: And if, by chance, some very, very tiny bits get through that sock filter somehow, most cars have a second, multi-micron-level filter further upstream to catch those even-smaller impurities and protect the fuel injectors.

TOM: So the car companies obviously have dealt with people like you before, Bob. And they were ready for you this time. I think you can sleep easy.