How much fuel does turning the car on consume?
 

I read somewhere that when you start the car, it consumes about as much fuel as it takes to idle for one minute. If that's the case, why do people shut their car's off at intersections? Is there any truth to this statement which I heard?

That is a myth, v6=5 seconds payback period
https://www.memagazine.org/june07/dep...input_out.html

well i know each time the key is turne doff and back on the car primes the fuel pump to regain the pressure possibly a bit more so im sure excess fuel gets sprayed past the injectors. ive heard about the same hting but if your leaving your car idling for more than 30 seconds its better to shut it off. but that was years ago so maybe now with new technology in cars its now a minute...

skewbe, thanks for that link.
I don't think I am going to shut my car off at an intersection, because it is putting extra wear on a starter. The amount of gas saved won't pay for itself at all if my starter needs to be replaced...

I've heard the injectors firing at startup is equivalent to ~10-15 seconds of idling, and I'm sure you could answer that definitively w/ some manufacturer specific information. Or someone who has some experience programming ECU memory could probably give you a decent idea of the difference in duty cycle. You can also get a remanufactured starter from most auto repair chains w/ a lifetime warranty for less than $100. Starts will kill a starter slowly, but most of the time they die out from prolonged operation/undervolting based on what I've read.

Shutting your car off for a red light seems ridiculous. Unless it's a 2+ minute wait. Most lights around here are 30 seconds.

phantomcow2, veloman: Again, please try and keep an open mind. We've already busted one rediculous myth in this discussion. You may decide that idling and getting 0 MPG isn't for you.

In my experience, I am 99.999999% of the time coasting up to a stoplight with the engine off anyway, I simply don't restart it until it is time to go (assuming I wasn't able to keep moving and bump start it).

Do you guys have a stick or an automatic?

I was telling my friend about turning the engine off at red lights and he seemed to think the lights are only 15 seconds. The only light here that lasts for 15 seconds is a green turn arrow for 20 seconds most lights in Louisiana are pretty long many red ~1 minute. Sometimes a light will seem to have malfunctioned and take forever! At any rate, every second you idle while stopped you have to average that time at 0 mpg. Ever failed a test? Averaging 0's can drop your mpg pretty good.

Turning it back on in an auto is a serious PITA, so unless you can time the lights perfectly, you could just blow a green light trying to turn it on. It happened once, I was pissed, and the lady behind me was pissed more. And, my guess is that you would save about a tablespoon max, not really worth the trouble, I think.

Is the fuel needed to start a diesel engine the same to start a petrol engine? Or is it relatively more? I'm asking this beacause a diesel engine needs more energy at the start to make the pistons moving. In that case, I should shut down the engine if I expect to be stoped for a long time, lets say... 40 secs, 50 secs or more.