Motormouth: Turn off engine to save money at drive-thru

Q: I was wondering if there's a rule of thumb for shutting off a car while waiting in a drive-thru lane at the bank, pharmacy, coffee shop, etc. to conserve gas. If I think I'm going to be idling more than a minute, I shut off the car. Does this make sense, or should I just let the car idle? Does it take more gas to restart the car?

A: I do the same thing, even on my motorcycle. It does not take more gas to restart the engine. There is, however, a comfort issue. Turning off the car also will, of course, turn off (depending on the season) the air conditioning or heater.

Q: In Minnesota, we are required to have our headlights on when it is raining. I notice that many cars have headlights (running lights?) on, but their taillights are not on. Sometimes, at night, cars have headlights on, but not their taillights. This seems to be a road hazard. It is difficult to see a vehicle from behind at night or in a rainstorm if their lights are not on. Are running lights a feature on most cars?

A: Although daytime running lights (DRLs) are compulsory in some states, there is no federal law. As you have noticed, DRLs do not also turn on the taillights. Most carmakers have linked the headlights with the windshield wipers. Although most cars now sport independent DRLs, early vehicles simply illuminated the high beam filament at a lower voltage to glow dimmer.

Q: On vehicles that have a manual transmission and tachometer, is it better for gas mileage to target an optimum rpm for shifting rather than a speed for maximum gas mileage?

A: Peak torque on the rpm curve seldom yields peak fuel economy. The highest possible gear plus slower engine speed is the sweet spot.

Q: My father gave up driving and gave me his low-mileage 2015 Hyundai Genesis. It has trouble starting after sitting for a few days. I had two mechanics look at the car, and both said that the charging system is fine, including the battery and alternator. They both said you have to start the car and let it run every couple days. I think that's ridiculous. I've had cars that sat for weeks and started right up. I think there has to be a draw somewhere.

A: There might be a parasitic electrical draw, as you suspected. Although some current is always flowing to keep the car's control systems alive, anything over 500 milliamps (one-half amp) is too much. This is easily tested using an ammeter. Talk it over with your mechanic. By the way, letting the car idle does not charge the battery very well.

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 motormouth.tribune@gmail.com.