Turning on ..Turning off

Ever since I had my first automobile, I was told *its better for the battery and/or the engine to start the engine and THEN turn on the air conditioning and the headlights (if needed). I have been doing that ever since. In addition, I turn the air and headlights off before I turn off the engine. Is it still a good idea to start the engine first? or am I following an Urban Legend? Its obvious that other than turning on the ignition, I know very little about cars.

I’ve been told similarly. The explanation I got was that if your lights are one when you attempt starting the car, it puts more strain on the battery and reduces it’s overall electrical life. I have not heard it applied to the car air conditioner, though.

If you think about it, it makes sense. Say your battery is just barely to spec on its electrical charge. That means it has just enough juice to turn over your engine and start the car. If your lights are on first, there’s not enough juice available to turn over the engine AND keep the lights on, so it doesn’t start.

“If God had meant for man to eat waffles,
he would have given him lips like snowshoes”
-Rev. Billy C. Wirtz

I’ve was taught to do the opposite in this certain circumstance: when it’s bitterly cold and your car won’t start - especially if it won’t crank at all - turn your headlights on for about 5-10 seconds, then try to start. Most of the time, it works. (Sometimes I had to wait 30 seconds.)

The explaination I got was that with the battery so cold, it didn’t have near the power available to run the solenoid. But the headlights will operate no matter what the power (except for no power). The small amount of current will start to warm the battery “juices” to the point that the battery can then start the engine.

I don’t know if the science is right; I just know it worked.

Wrong thinking is punished, right thinking is just as swiftly rewarded. You’ll find it an effective combination.

The more things that you have turned on the greater the starting load on the battery. The biggest load comes from your starter motor. The load increases with big load items like, air conditioners, headlights, and power amps, etc. Starting loads that are too large can cause incremental damage to the battery so that ultimately your battery life can decrease… This bit of conventional wisdom is slowly becomming moot, because many modern cars are starting to put in smart circuits that prevent heavy load items from engaging while your starting your car.

This is true… at least, the part about battery efficiency in extreme cold. It’s not the solenoid, though, it’s the starter motor which requires a lot of current. When you use this trick, you should turn your lights back off before you hit the starter to insure maximum battery output goes to the starter.

I asked a very similar question a while back.

Here is that thread: