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Q: I've had two flat tires from nails this summer. In both cases, only the head of the nail was showing on the tread. How does a nail lying horizontal on the pavement reposition itself so that the point drives itself into the tire and leaves only the head showing?

A: The reason nails usually sink all the way in to the head is that the road works like a hammer, pounding in the nail as you drive.

Turbos are tough

Q: I drive a 2017 Jetta with a 1.4-liter DOHC turbo direct injection engine. It is my first car with a turbo. What, if anything, do I need to do to maintain the turbo?

A: Turbochargers are robust and need no special care. But if you have been hammering the car hard, such as on the racetrack, I suggest allowing the engine to idle about a minute before shutting it off to allow the turbo to cool a bit.

Plugging away

Q: When my car was still under warranty, an Audi service adviser shamed me for having my oil changed by an independent Bosch-certified mechanic using the gravity method. He advised I would void my warranty unless the dealer changed the oil using vacuum extraction as recommended by Audi. What's the real advice on this matter as I prepare for my next oil and filter change?

A: You can't go wrong pulling the drain plug. Some shops push the extraction method because it is quicker. But there is a risk of oil dripping from the hose during removal and a potential for an engine compartment fire. Remote? Maybe. But I am old-fashioned.

A gas gaffe

Q: My wife put about eight gallons of E85 in our new Ford Escape without realizing that she was using the wrong pump. Is this detrimental to the engine? The car had a quarter tank, and she filled it to three-quarters full.

A: For the past few years, the Escape has been a flex fuel vehicle, meaning that it will run on regular gasoline or E85. Even cars that are not flex fuel compatible usually will not have any problems if occasionally misfueled. Of course, fuel economy will be reduced until you burn off the wrong gas.

Ask again

Q: I have a 2014 Subaru Outback with 97,000 miles on it. I had it in recently for oil change and tire rotation. The customer service representative said I needed to replace both front lower control arm bushings and links immediately. The cost would be $895. I was surprised by this because I take it in routinely for maintenance and hadn't heard anything about those parts showing wear before. It drives fine. Should I get a second independent opinion?

A: I am a big fan of second opinions. But don't repeat what you were told at the dealership. There is a temptation to agree with the first diagnosis. Simply ask for a front suspension inspection.

Bob Weber is a writer, mechanic and ASE-certified Master Automobile Technician. His writing has appeared in automotive trade publications, Consumer Guide and Consumers Digest. Send automotive questions along with name and town to