Strong gasoline fumes may warrant a trip to the dealership

Prices are displayed above the different grades of gasoline available to motorists as they take to the road to start the Memorial Day weekend, Thursday, May 27, 2021, near Cheyenne, Wyo. (AP Photo/David Zalubowski)
Prices are displayed above the different grades of gasoline available to motorists as they take to the road to start the Memorial Day weekend, Thursday, May 27, 2021, near Cheyenne, Wyo. (AP Photo/David Zalubowski)

Credit: David Zalubowski

Credit: David Zalubowski

Dear Car Talk:

Every time my wife fills up her 2008 Mercedes CLK 350, the garage reeks of gasoline fumes. We have had our local mechanic (not the Mercedes dealership) check it out and they found nothing.

We stop filling the tank before the nozzle clicks off, to make sure we’re not overfilling it, but that doesn’t help. The only thing that works is for her to fill up just prior to taking a longish trip, and then there are no fumes in the garage when we return home.

The fumes are very strong, and I am concerned about the possibility of fire. Thank you. -- John

Ray Magliozzi
Ray Magliozzi

RAY: A fire is exactly what you need, John!

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Actually, you’re right to be concerned. There are four things to check. One is the gas cap, in case it’s no longer sealing completely. The second is the filler neck, which can corrode on older cars and cause leaks. The third is the evaporative emissions equipment. And the fourth is the gas tank itself.

If there’s a leak in any of those places, though, it should turn on your Check Engine light. The fuel system monitors itself for leaks, and if it can’t hold pressure due to a leak anywhere in the system, it’ll turn that light on.

In any case, it’s not always easy to find a leak like this, so you’ll need a competent mechanic who is dedicated to tracking it down for you. You should obviously fill the tank just before dropping off the car. The mechanic will then put it on the lift and use his eyes (to look for a wet spot), his nose (to smell the fumes), and his hands (to feel for liquid gasoline) to try to figure out where gas is seeping out.

If he strikes out under the car, he should also try removing the rear seat and checking the top of the gas tank. That’s often overlooked. And these cars can develop a crack on the top side of the gas tank, where it’s bolted onto the frame. That’s something the Mercedes dealer might know to look for, but your regular mechanic might not.

In the meantime, stop sneaking out to the garage at night to smoke your Cohibas, John. Use the tool shed instead until this is fixed.

How soon is too soon to add highway miles to new cars?

Dear Car Talk:

Is this an old wives’ tale or is it true? I’ve been under the impression for over 50 years that it is a good idea to get a new car out on the highway as soon as possible. I understood that it helped to get the car to a good operating temperature for an extended period of time on the highway, and that this would provide a good seal for all gaskets.

I did this with my 1973 Pinto (I know, one of your favorites), and it ran very well until I sold it in 1982 for $350 with a hole in the floorboard (good view of the road). I bought a 1985 Chevy Astro Van (I think this is one of your favorites, too, right?) and within a few days, drove it to Colorado and back. I recently purchased a brand-new Honda CR-V and have already put about 100 highway miles on it.

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My experience has been that I have had relatively few major problems with all of the cars that I have purchased after doing this. Have I just been lucky? Or am I right about this? -- Tom (’73 Pintos were the best)

RAY: Well, now that I have a complete automotive history on you, Tom, I’ll be able to refer you to the appropriate support groups.

I don’t think your early highway driving has anything to do with your automotive good fortune, Tom. If you can call owning a Pinto and an Astro Van in the same lifetime good fortune. If your cars did do better than other Pintos and Astro Vans, it was probably because you drive gently and take good care of your cars.

In fact, new car manufacturers instructed owners to do the exact opposite of what you did.

When you bought those two beauties, in the ’70s and ’80s, carmakers recommended that you NOT drive their new cars on the highway for extended periods. They wanted you to vary the engine speed constantly during the first 1,000 miles and not drive at sustained highway speeds. And many of them wanted you to stay below 60 mph or so.

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That was known as the “break in” period. Or as Pinto owners used to call it, the “break down” period. It was thought that varying the speed of the pistons would help the new cylinder rings “seat” or conform to the exact shape of the cylinder walls and thereby prevent oil burning later on.

That’s because manufacturing just wasn’t very good back then. The spaces between fitted parts (called tolerances) were huge by today’s standards. For the last 25 years or so, tolerances have been tiny in comparison. So there’s no longer any need to “seat” the rings. They come seated. How’s that for progress? They’re actually making parts that fit together perfectly, right from the factory.

When you combine that with the huge improvements in oils over the last few decades, you can take your new CR-V right off the lot and drive it in the Baja 500. It’s all set.

And it’s such a well-made car that if you drive it gently and perform the recommended maintenance, you should still be driving this car 200,000 miles from now, hopefully without a hole in the floorboards.

Got a question about cars? Write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.

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