idling the engine vs restarting

[autumnleaf]

OK, leaving the engine running idle uses fuel. Starting the engine also uses fuel. How long before it costs more to keep the car running than it costs to restart it? I.e. if i'm waiting for 30 seconds, should i turn the engine off? 5 minutes? Half an hour?

I've done some googling on this but the advice is vague or contradictory.

 

[mayoman2]

I think you should consider it is not good leaving you car idle for any great time, maybe give it a minute after you have done a journey or so or before you start your journey. IMO forget about the difference in fuel but more on how bad it is for you engine been left idle for long period

That my opinion anyway

 

[Superman]

I've seen signs in Germany asking cars to switch their engines off while waiting for a train to cross.

 

[Satanta]

This gives some information (which seems well founded) on the emissions side of things, not so much on the fuel economy though.
I'd suggest that if the car is producing more emissions then it's possibly burning more fuel, but didn't spot any "real" info on that.

Some interesting comments [broken link removed] and a small section [broken link removed].

Seems to state if your idle for more than 60 seconds your better to turn off the car.

 

[smcgiff]

The rule I've heard is that you leave it in neutral at traffic lights, but switch off if you think it's going to be longer, ie traffic jam or (as mentioned above) waiting for a train. But, the occassions would be fairly limited.

The only other situation comes to mind is if you're stuck behind a lorry driver and they stop to talk to another lorry driver coming in the opposite direction, then ye may as well switch off the engine!

The above rule is a bit subjective, as the length of time traffic lights are red tend to vary between traffic lights.

 

[Parker]

On the emissions side of things......turn it off if you want to


On the economy side of things....it makes a big difference....I get the train to work and drive to the station....im there probably 20 mins early and to sve the battery in the mornings while listening to the radio I used to leave the engine running....as a test i filled the tank and did my normal routine....noted the miles......then filled the tank again and in the morning turned off the engine and lsitened to the radio on my mobile......got 60 more miles with that tank...makes a big difference...

On the wear and tear side of things......its not bad for your engine internally.....but starting your car more than you need to will wear out your starter motor....lessen the life of the flywheel and increase stress on belts