Q: The difference between a coupe and a sedan was explained to me many years ago by an old body and fender guy. When you open the door, there is no window frame. All sedans have window frames, and are generally more solid cars because of this support and the door post. You can have two-door sedans, but not four-door coupes. Also, the rear windows on the coupe, when rolled down with the front windows down, create a complete front-to-back opening. No center post. Hope this helps.

J.S., Chicago

A: It has been a long time since collision repair specialists were called body and fender men. It has also been a long time since coupe and sedan were so clearly delineated. Carmakers play it fast and loose with body style terms nowadays. According to the CarMax website: "The coupe car term started to blur as manufacturers greatly diminished or completely removed the rear seat to create a sportier 2+2 body style. This term refers to cars that have a sleek, sloping roofline, two doors, and two functional seats up front, plus two tiny seats in back. More recently, auto manufacturers started to apply the coupe definition to the sporty variants of their sedan lineup. As a result, the coupe term has become more popular with manufacturers, who apply it more loosely. Automakers may also offer both a coupe and sedan using the same model line, like the Honda Civic. The ability to clearly define coupe vehicles has become challenging in recent years as a result." We recall when the B-pillar (the center post between the front and rear doors) disappeared on four-door cars that were called hardtop sedans. Ugh.

Q: Just thought I would chime in on this auto-stop feature showing up on so many cars. I don't get the need for this at all. The people I know that have this hate it. If they can disable it, then they do. Friend just got a new Buick two months ago and is already thinking of getting rid of it. I'm interested in a new LaCrosse, but it's on that, too. I'll keep what I have for now. What is the real need for this?

K.U., Schaumburg, Ill.

A: The need? Improved fuel economy. Car manufactures are using every trick they can think of to extend their CAFE (corporate average fuel economy) numbers. Five years ago, the government set a target fleet average of 54.5 miles per gallon for model year 2015 (the adjusted mpg we see on stickers and trip meters is about 40 mpg). Other tricks include cylinder deactivation when only four of the eight cylinders are required, hybrid technology and more.

Q: When I fill up my motorcycle, I usually get premium gas. If the person before me filled their tank with regular, and I buy only 3 gallons, how much premium gas am I getting if it all comes out of the same hose?

M.K., Chicago

A: There is roughly one quart of gasoline left in the dispenser's line, so look for gas stations that have separate nozzles for each fuel grade. Or, wait for a pump where someone has just filled with premium. But it is not as bad as you may think. Petroleum industry chemist Tom Wicks told us that one quart of regular grade at 87 octane mixed with premium at 93 octane would only take it down 0.75 to 1 octane number, so you might end up with roughly 92 octane in the tank.

Bob Weber is a writer and mechanic who became an ASE-certified Master Automobile Technician in 1976. He maintains this status by seeking certification every five years. Weber's work appears in professional trade magazines and other consumer publications. His writing also appears in automotive trade publications, Consumer Guide and Consumers Digest. Send automotive questions along with name and town to motormouth.tribune@gmail.com.