Turn it off, or let it idle?
Q: I was wondering if there’s a rule of thumb for shutting off a car while waiting in line at the bank or pharmacy or coffee shop, etc., to conserve gas. If I think I’m going to be idling more than a minute, like at the bank, I shut the car off. Does this make sense, or should I just let the car idle? Does it take more gas to restart the car?
— N.M., Elk Grove Village, Illinois
A: I do the same thing, even on my motorcycle. Of course, there is an added reason on the bike. It gets hot down there.
My rule of thumb is: If it seems like a long time, shut it down. It does not take more gas to restart the engines.
Q: I have a 2018 Hyundai Sonata. I deliver meals on wheels two days a week. Is it better for gas mileage, when making short stops, to let the car run or turn it off and then restart? — M.M., Easton, Pennsylvania A:
See the answer above. (And thank you for volunteering.)
Q: I read a comment about running lights on cars. In Minnesota, we are required to have our headlights on when it is raining. I notice that many have headlights (running lights?) on, but their taillights are not on. Sometimes, at night, cars have headlights on, but not their taillights. Are the running lights only illuminating the headlamps and not the rear lights? 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? — J.L., Minneapolis, Minnesota 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, so both activate during inclement weather. 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 more effective to target an optimum rpm rather than mph for maximum mpg? — C.P., Downers Grove, Illinois A:
Not necessarily. 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 93-year-old father finally gave up driving and gave me his low mileage 2015 Hyundai Genesis. I had two trusted mechanics look at the car and both tell us that the whole 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 have cars that sit for weeks and start right up. I think there has to be a draw somewhere. — M.S., Addison, Illinois A:
There may 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 connected between the negative battery terminal and the cable once it is removed. There an interval step to keep the car’s system alive while the battery cable is disconnected using a jumper wire. This step can be avoided using an amp clamp. 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 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. Send questions along with name and town to motormouth. tribune@gmail.com.