Q: I enjoy reading your column in my Sunday Philadelphia Inquirer. My question: Does it weaken the car's battery if the headlight (not DRL) switch is in the "on" position when the car is being started? Someone I know leaves the headlights on when shutting off the engine, so that they don't forget to turn them on next time they start up. Seems to me this is a needless drain on the battery. But then I wonder if that is correct, as some late-model cars shut off at idle for traffic lights, etc., in order to save fuel and help with emissions.
Eric P, Audubon, N.J.
A: I'm a bit confused by what you're asking. It's best to not have any vehicle lights or accessories on/active when starting the engine, especially during cold weather. The objective is to allow the battery to do two things only, supply needed current to the engine's fuel and ignition management systems and starter motor. If one had a robust, fully charged battery, during warm weather, it wouldn't be a big deal. The ignition switch in most vehicles momentarily cancels accessories as the engine is cranked, for this reason. Cold weather is a tough situation, as battery performance is reduced and cranking a cold engine requires more juice.
I wonder if your friend is leaving the headlight switch in "auto," this wouldn't be a problem at all. You sure wouldn't want to leave the headlights truly on while parked because after two to three hours the engine would likely not start. Vehicles employing stop-start engine management closely watch electrical consumption while off and may either suspend the feature or cut it short if battery strength falls or climate control needs are high.
Speaking of stop-start, I did receive a fair number of comments regarding this feature. Many don't care for it and have found by only lightly depressing the brake pedal when stopping they can suspend operation. I wonder if this could result in fewer rear-end collisions? Sunny loves the feature in her 2017 Lincoln MKZ because it can be turned off continuously! George says his two vehicles (2015 Mercedes S550 and 2016 GLC) do stop-start so smoothly he can't imagine why anyone wouldn't like it. Finally, Dana likes how it works in his 2015 Ford F-150 because he can depress the brake deeply at long stop lights stopping the engine or lightly for short stops, and it keeps running. Dana says after you get used to the feature it feels odd to sit at a stoplight in other vehicles that keep the engine running!
Q: Reading your column in the Dec. 17 Dubuque, Telegraph Herald. You say that running the A/C compressor reduces gas mileage by perhaps 1-2 MPG. That is probably true with belt driven compressors. I used to be able to feel the change in older cars. But now we drive cars with electric motor driven compressors (Toyota Hybrids). Is the same effect at play there? I can't tell when the A/C kicks in or out.
Wayne C.
A: Great idea looking at this from a hybrid/electric angle! The electricity needed to run your a/c compressor will still require gasoline to make the electricity, or utilize power company electricity, and the horsepower needed to turn the compressor likely isn't significantly different than a belt driven unit. I've noticed perhaps a 15 percent decrease in driving range in my '17 Chevy Volt when using the defroster (A/C compressor running) along with some heat _ when it works....
