They once said that you’ll wear out the motor twice as fast if you start the car while the light switch is in the ON position, beccause it takes much more power to start both the car and the lights.
My car has an AUTO lights function, whereby I leave the switch on Auto and the light sensor determines whether or not I need my headlights on, according to ambient light levels. I haven’t touched the headlights switch since I bought the car a year ago.
But am I wearing out the motor by leaving it in AUTO? Is that the same as leaving it in ON?
If I operate the lights manually, they are either on or off; I don’t run with parking lights. But the Auto function always has the lights on, even just the parking ones. So how much damage is that causing when I turn off the ignition?
My mothers’ car had this Auto function, but the headlights did not come on while the ignition key was in the start position; only after the car was started and the key released to the on position did the headlights come on.
I am skeptical that it wears out twice as fast, although they are generally trustworthy.
I have the semi-annoying type of lights which always come on when it is dark, and I have no switch setting to suppress that. However, the lights don’t actually come on until I put it in D or R (or forward gears less than D) and move a little bit. In other words, the lights will never turn on when I start it unless I manually flip the switch. Does the AUTO setting work the same way?
By “motor” I assume you mean the internal combustion engine (hereafter referred to as the engine) that moves the car forward. When you start the car, the engine isn’t running; you are using a small but powerful electric motor (hereafter referred to as the starter) to spin (crank) the engine until it starts firing on its own; then you release the key, the starter disengages, and the engine is running.
That means that the engine itself doesn’t really care what else you’re doing to the car while it’s starting.
However, the battery does. The starter draws a LOT of current from the battery during a start, and most cars include a load-shedding relay that automatically shuts off most or all of the electrical accessories while you’re cranking the engine so that the battery can give its all to the starter. Next time you start your car with the headlight switch in the “on” position, watch to see what happens when you turn the key to start; I’ll bet the headlights shut off, and then turn on again when you release the key. If that’s the case, then what you do with the headlight switch makes absolutely zero difference to the engine, starter, or battery.
Even in the odd case that they don’t shut off during a start, things will be fine. As described, the battery will see extra electrical burden from the headlights, but not much in the scheme of things. Your headlights are about 55 watts each (less if you have HID’s), so 110 watts total; for a 12-volt system, that means they are drawing about 9 amps of electrical current. During a start, the starter draws hundreds of amps from the battery. That figure can vary widely depending on whether the engine is warmed up from having recently run, or cold as hell from sitting overnight in Anchorage. 9 amps of current flowing all night because you left your headlights on will of course kill the battery, but 9 amps of extra current for a couple of seconds during a start won’t make any significant difference to the engine, starter, or battery.
How does starting the engine with the lights on cause the engine to “wear out” twice as fast?
I could understand it causing stress on the battery as it would need to deliver more power (CCA or cold cranking amps) to run the lights and the starter motor at the same time, but am skeptical that it would cause harm to the engine.
In more recent cars, I don’t think such a scenario is even possible. Like t-bonham’s mother, my car only lets the headlights come on after the car is started, at which time, they come on automatically.
Plus I think they are ‘semi-retired’ and reuse a lot of old material on their show now. They haven’t had a new puzzler in many months.(at least I recognize a lot of them from past shows)
Ohh… Click and Clack said this? In that case, I’ll wager what they really meant is that it causes Ray’s underwear to wear out faster. Their advice is usually OK, but every now and then I think they’ve been sniffing too much carburetor cleaner.
Click and Clack are entertainers. I put zero credibility in their auto advice. Now starting the car with the headlights on is hard on the battery and starter motor due to higher current draw and lower voltage. This would result in a slower cranking speed and maybe a slower start. I find it highly unlikely that would cause much difference in engine wear. I would want to see a cite of an SAE paper before I believed it.
I am sure the headlights are wired to not come on as long as the engine is in start mode.
Keep in mind that in their show they’re providing entertainment with some information thrown in. They’re not trying to give a seminar on automobile function and repair that will withstand scrutiny for accuracy. One can certainly learn some things from them, but their modus operandi includes humor, exaggeration, and omission of a number of details that would bore many of their listeners.
Starting with the headlights turned on won’t affect the engine. Having the lights on for those extra few seconds (irrespective of operating – or not operating – the starter) the means a bit more work for the alternator, but not to any appreciable degree.
There are two concerns. One is it reduces the power available to the starter. Starters typically draw in the neighborhood of 150 amps, maybe 200 or so for a large engine, and headlights typically draw about 10 amps. In a marginal situation, say very cold weather and/or a partially discharged battery, siphoning off some of the battery’s juice to the lights might make the difference between the starter being able to get the engine started or not. It’s not terribly likely to prevent starting, but nevertheless it’s wise to have the lights off on a January morning in Chicago.
The other concern is that while the starter is cranking the voltage to the headlights is reduced. Halogen lamps (the vast majority of headlights in service nowadays) are sensitive to this, and the life of the bulbs can be shortened by running on the reduced voltage. This isn’t a huge deal, but it’s the most likely negative consequence of starting with the lights on.
Look, I’m not a car person, and because nothing about what goes on under the hood makes any sense to me at all, they probably did say BATTERY or STARTER and not engine.
Be that as it may, though, my question remains the same, and I thank the people who gave logical explanations.
In my car, a 2011 model, once you set the lights to AUTO you never have to touch them again. They stay on for 30 seconds after I cut the ignition and then turn themselves off. I haven’t noticed if they are on after I get in but before I push the ignition switch, because I’m in the car and can’t tell. I had a 1997 that worked the same way; after turning it to Auto, I never once touched the light switch in the seven years I had the car.
I’m pretty sure it’s the starter motor they are talking about and they seem to have a point. During cranking you draw down the battery voltage pretty significantly, any added load would further surpress that voltage. Less voltage typically not good for a motor.
As for the engine itself I don’t think it cares either way.
A fairly simple trick for a single person to test their car lights and blinkers is to park just a few feet away from a big flat wall or your garage door at night. You can use the reflection to test you headlights, brights and blinkers without having to get out of the car. You could also test whether you car lights turn off when you start the engine.
If this is one of those fancy keyless entry models where they key fob stays in your pocket and you push a button on the dashboard to start the engine, then almost certainly the headlights aren’t coming on until the engine is running. If that’s the case, then it doesn’t matter whether you have the headlight switch in “AUTO” or “OFF” when you start the car.
I would need a cite for that statement before I even consider analyzing the rest of your post. Because I used to think that was true and Tom and Ray was who explained to me that it isn’t.
Their advice is usually OK, but every now and then I think they’ve been sniffing too much carburetor cleaner.