Lets say you are waiting for a friend to come out and the wait is 10 minutes. I understand when you idle the car it's using up gas, but you also use up a good amount of gas when you restart the car and it also causes wear on the starter. Which is better? just idle it for 10-15 minutes or turn off the engine, wait, then start it up again.

 

Drive around the block.....more fun driving vs sitting.............

 

thats only for carburetors, since when they start they use alot of gas.. now with fuel injection it is wasteful to leave it running. most hybrids just turn off the gas motor at a stop no matter how they are running since its a waste of gas.

 

There are several cars with start stop built in. It turns car off even at stop lights. Why would it take more fuel to start a car then it would to keep it running?

 

Neither....go do some doughnuts while you're waiting.

 

If your car had a really good exhaust note, you wouldn't be asking this question.

 

Kill it and restart. I stop my car in a slow drive through lane sometimes, and its got over 250k on the starter, no issues.

 

I don't know... carbs only use gas if you push the pedal which sprays the accelerator pump. I can start my old carb F150 after its warmed up without touching the pedal and it fires immediately at the level of idle.

Whereas every time I start my Bullitt there's a slight increase in rpm's that quickly drops back to idle - even though I don't touch the go pedal.

Either way, no need to idle for 10 mins. Loads up the engine.

 

As some others said, I think the whole starting uses more gas is a myth. Obviously depending on the weather outside and how long you will be sitting would determine which to do.

10 mins probably shut off.

Also remember in the ford manual under oil changes it says extended periods of idling under the "extreme use" category. So I guess that causes engine wear or weakens oils?

 

I've heard that though modern cars might not use excess fuel on start-up, they do highly pollute at that time because the catalytic converters aren't warmed up? Of course that would only be at a cold start... stop-start in traffic or waiting 5-10 minutes I wouldn't think would do any harm.

 

That's correct. Its dirtier at a COLD startup as the CATs are less effective when cold. This is why when you start the car in the morning, the car will rev itself up a bit above a warm idle to warm the cats faster and reduce emissions. This is a non-issue for the OP use case however.

 

OH SNAP! lol

Seriously, I'd go cruise around and pick him/her up in 10

 

My input here is going to be a shot in the dark but my 2008 V6 manual suggests killing it for long period of idling

 

10min, it doesn't really matter, doesn't hurt anything, not much fuel used. On some cars however, you don't want to idle for 45 min strait, but that's for older cars with less eficient cooling systems I.e. mechanical fan vs. Electric fan. Just note that idling = 0mpg

 

Up here in canada id wanna keep it going...be **** cold after 10 min wait without motor going and heat...

 

In Europe (Germany), it's against the law to "idle" the engine for more than a minute (polluting?).
While working there a few years ago in the winter, I started up the rental car at a hotel parking lot to get the windows to defrost. A lady across the street starting yelling at me in German (I knew a few of the words...). Another younger person translatted to me saying she was telling me to shut down the car, as it was illegal to let the car idle.
While idling in traffic for more than a minute in large German cities, you're supposed to shut off the car. I guess this is why some newer models do it for you.
This is also why higher end vehicles like the BMW's, Lexas, Mercedes, and others have an electric heater that will run when the engine is in the auto off/on mode.

 

Anything longer than a minute, shut 'er down. No need to waste fuel, oil life, fan motor life...and of course the minute wear and tear on rings, bearings, etc...which adds up over a lifetime if you make idling like this a habit.

Plus...gasoline/oil is an insanely valuable resource. The times we live in are all about taking it for granted but there has never been a more easily accessible source of an incredible amount of "work" and there may never be again and when it's gone, it's gone. If you're going to burn it, you might as well either be enjoying the hell out of it or putting it to use. Just converting this energy into heating the atmosphere while you wait is a shameful waste.

 

Yeah, it's 20*F here right now, so the car stays running!

 

10 minutes - shut it off
1-2 minutes - keep it running
In-between - you are on your own

 

IMHO, as long as the engine is warm and your battery is in good shape, kill it and restart.