CLICK & CLACK : Gas-Cap Gasbags

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Sunday, June 28, 2009

Dear Tom and Ray:

When my husband and I first got married (18 years ago), I noticed that when his car was low on gas, he would remove the gas cap, saying it would make the gas last longer until he could get to a station. I am a college-

educated woman, and this seemed preposterous to me ... but then I noticed other people doing it. My husband has since stopped doing this, due to my nagging. But is there any truth to this, or is it just some urban legend? -- Tina

RAY: When the power goes out at your house, does your husband also run outside and disconnect the electric line from the pole so he can suck more electricity through the house's wires and catch the end of the ballgame?

TOM: He's nuts, Tina. I imagine his thinking (or his father's or grandfather's thinking, more likely) is that getting fuel from the gas tank to the engine is like pouring soda out of a two-liter bottle. And while it glug-glug-glugs out, if you were to punch a hole in the bottom of the bottle with an ice pick, you'd allow more air in, and the soda would pour out more quickly.

RAY: But the gas tank is not a soda bottle. First of all, nothing "pours" out of the gas tank. The gasoline is "pushed" out by an electric pump that sits right at the bottom of the tank.

TOM: And second, the pressure inside the tank is carefully managed by the fuel-tank ventilation system. That's done so that gasoline vapors don't constantly waft out into the atmosphere and make every place on Earth look like Los Angeles.

RAY: In fact, if you drive with your gas cap off, or even loose, your "check engine" light will eventually come on. The computer will conclude that the fuel system can't hold pressure, and will warn you that you need to have the car serviced.

TOM: In the old days, gas caps had pinholes in them and gas was sucked out of the tank by mechanical fuel pumps driven by the engine. So that's probably where this theory originated. Even then, I'm dubious that removing the gas cap would have made any difference.

Dear Tom and Ray:

I'm tired of waiting for the American auto industry to come up with an affordable all-electric car, so I'm looking seriously into buying a Chinese-made Flybo. I know it has a top speed of 43 miles per hour, and lacks a lot of basic safety and comfort extras (no air bags, no heat) but the same is true of the 1987 Dodge Raider I'm driving now. My question is, how easy will it be to service this car? I don't know of any Flybo dealerships in the U.S. What could go wrong with this car, and how can it be fixed? -- Kate

RAY: Kate, you are about to join the wacko fringe. You know those guys who live in yurts, feeding themselves off their own homemade acorn granola and squirrel yogurt? Ask them about their Flybos.

TOM: We admire your environmental ambitions, Kate. And we agree with you that electric propulsion is probably where cars are eventually heading. But it's very difficult to be an early adopter, especially when you're adopting something that has no serious support network. So, unless you're married to a very handy electrical engineer, who happens to live in a yurt, you're almost certainly sentencing yourself to years of trouble in finding parts and people willing to work on this thing.

RAY: Here's what we'd recommend instead: Adopt the best-available, widely supported current solution. Hybrids like the Toyota Prius, Honda Insight and Honda Civic Hybrid are getting 40 to 50 miles per gallon. And they're doing it with all of the latest and greatest safety equipment.

Got a question about cars? Write to Click & Clack in care of The Post, or e-mail them by visiting the Car Talk Web site at http://www.cartalk.com.

Copyright 2007 by Tom and Ray Magliozzi and Doug Berman


© 2009 The Washington Post Company

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