How much gas does starting the car use?

January 30, 2006 4:10 PM

Do I waste more gas by letting the car idle for 5 minutes or by turning off and restarting?

I always heard that starting the car uses alot of fuel.

posted by SwingingJohnson1968 to travel & transportation (25 comments total)

4. Minimise fuel wasted in idling

Minimise fuel wasted in idling by stopping the engine whenever your car is stopped or held up for an extended period of time. By having the engine switched off, even for a short period, you will save more fuel than is lost from the burst of fuel involved in restarting the engine. The net increased wear and tear from this practice is negligible.

(Source. But it's the Australian government. No figures to back it up, natch.)
posted by disillusioned at 4:13 PM on January 30, 2006

Idling for just 10 seconds uses more fuel than restarting an engine and actually causes more engine wear, according to this site. Googling "car idle 10 seconds" brings up many similar results.
posted by stray at 4:14 PM on January 30, 2006

I'm told this *used* to be the case - but now cars start more efficiently, making the first two comments correct.
posted by tiamat at 4:22 PM on January 30, 2006

You do if you have a prius or Honda hybrid.
posted by delmoi at 4:28 PM on January 30, 2006

There are a couple of schools of thought.

The first says that it's a pretty even tradeoff between cost of fuel and cost of engine wear. Figure if you turned your car on and off like that every day all winter, you'll probably knock a few thousand miles off the final odometer reading before a rebuild. So either idle and pay for it now, or pay for it later when you have to get a new (whatever). That's fine when gas is only fifty cents a gallon.

Nowadays I'm not so sure. Car engines are engineered really tight these days, and every spare scrap of fuel economy is being wrung out of increasingly expensive gas. I'd say a properly maintained modern engine (provided you changed the oil like a good car owner should) will last you three or four hundred thousand miles--that's a shitload of idling over time and gas isn't getting any cheaper, so you're better off turning the car off.
posted by Civil_Disobedient at 4:33 PM on January 30, 2006

Click and Clack on saving gas by idling as opposed to stopping and restarting: "It's complete B.S."

Modern starters can more than handle the wear-and-tear from shutting off and restarting frequently and it takes little to no gas.
posted by ontic at 4:34 PM on January 30, 2006

you will save more fuel than is lost from the burst of fuel involved in restarting the engine

Well, not to criticize the Australians, but I would think that you'd also have to use some gas to top the battery back up, since the starter puts a heavy load on it to turn the engine over.
posted by smackfu at 4:34 PM on January 30, 2006

Electronic fuel injection and electronic chokes means that it's a thing of the past. You would use more fuel for a couple of seconds at most. At the lights, turn your car off if you're confident you can restart it in time.

Note how hybrids often turn their petrol engines off when stopped these days?
posted by wilful at 4:35 PM on January 30, 2006

I drive a Honda Civic Hybrid and this is one of the ways it is designed to economize fuel. When I come to a stop the engine automatically shuts off, and stays off until I take my foot off the brake.
posted by Meredith at 4:41 PM on January 30, 2006

Also have a gander at this related recent thread.
posted by hangashore at 4:47 PM on January 30, 2006

Just to clarify, when discussing cars, does "modern" mean 'since 1995', 'since 2000', or what?
posted by kimota at 5:25 PM on January 30, 2006

when discussing cars, does "modern" mean 'since 1995', 'since 2000', or what?

In this particular discussion I would say it includes any car with fuel injection.
posted by kindall at 5:54 PM on January 30, 2006

I feel like I should point out that I have changed a lot of starters in my day. In my home town there is a prospering business whose entire purpose is rebuilding starters and alternators.

I do think that starter failure has as much to do with chronological age as it has to do with use, though.

The real way to solve this question is buy a car with a standard transmission and push start it all the time; that way no emissions (when it's turned off, anyway) AND no problems with broken starters.
posted by tcobretti at 7:27 PM on January 30, 2006

At the lights, turn your car off if you're confident you can restart it in time.

An exceedingly poor idea in terms of accident risk control.

With the engine running you have many more options available to you when faced with an oncoming accident situation.

You shall want to evaluate the reduced mobility and control options, before deciding that being parked dead-engine in the middle of traffic is a good idea. I should imagine the answer is highly situationally-dependent.
posted by five fresh fish at 7:29 PM on January 30, 2006

There are a couple of schools of thought.

And one of these schools is wrong. As tiamat said, it used to take more gas to start a car than to let it idle for a while, but not anymore. Mercedes actually did a demonstration at a car show about six years ago (maybe more) where they turned a car on and off repeatedly for a minute, measuring gas usage precisely, to demonstrate that it takes more gas to idle the engine than to start up your car again.
posted by Dasein at 9:28 PM on January 30, 2006

Along 5ff's line of thinking: if you kill the power, you kill your power brakes. That's no good.
posted by Civil_Disobedient at 11:45 PM on January 30, 2006

Also, on (non) preview:

to demonstrate that it takes more gas to idle the engine than to start up your car again

While that was what the OP asked, the first point I made was comparing your overall costs, not gas costs specifically.
posted by Civil_Disobedient at 11:48 PM on January 30, 2006

As has already been said, yes, you do waste more, and 5 minutes sounds like a lot to leave the car idle.

Definitely do *not* turn it off at the lights though - you're asking to be bumped, or at least piss off the drivers behind you being held as you restart the car.
posted by funambulist at 2:24 AM on January 31, 2006

Our local paper had an article on this recently and amongst the other facts it said that you should shut off the engine for any idling longer than 30 seconds.
posted by furtive at 7:31 AM on January 31, 2006

For what it's worth diesel-powered buses here in Tokyo cut their engines when they come to traffic signals.
posted by armage at 7:58 AM on January 31, 2006

tiamat writes "I'm told this *used* to be the case"

Pre electrically controlled carbs (and later electronic fuel injection) there wasn't much feedback to the carb whether the engine needed cold start enrichment or not. Considering that the consequence of no enrichment when needed (no start) is much worse than enrichment when warm (momentary rough idle and wasted gas) manufacturers of course went with wasting gas. The enichment pumps on a 800CFM four barrel will move an amazing amount of gas, wildly more so than the same carb at idle at full vacuum.

Civil_Disobedient writes "Along 5ff's line of thinking: if you kill the power, you kill your power brakes. That's no good."

All brake boosters have at least one hard stop of reserve capacity when the engine has been recently running.
posted by Mitheral at 8:36 AM on January 31, 2006

In Seattle, all the drawbridge approaches have signs warning motorists to turn off the car when waiting for the bridge.

Note, that turning your car off at every intersection might be illegal in many states. I know it's illegal to have the engine running, but be in neutral/park at the light, specifically because of the safety issues mentioned above by others....
posted by nomisxid at 10:18 AM on January 31, 2006

All brake boosters have at least one hard stop of reserve capacity when the engine has been recently running.

Unfortunately most drivers will be riding their brakes and releasing a lot of that built-up pressure before they realize what's going on. I personally would be annoyed to have to stand on my breaks. If I wanted to exercise I wouldn't be driving.
posted by Civil_Disobedient at 6:06 PM on January 31, 2006

Freudian typo:

my brakes, not breaks.
posted by Civil_Disobedient at 6:06 PM on January 31, 2006

The brakes are the least of the problem: without the engine running your power-assisted steering is going to be a bear to operate and -- just as importantly -- you can't accelerate.

The acceleration bit should not be underestimated: the ability to move even a few feet forward could make the difference between a costly rear-ending, and no rear-ending.
posted by five fresh fish at 9:30 AM on February 1, 2006