Hey guys, well I don't really have a "technical" problem here so to speak, but I always wondered... when I'm waiting in a bank drive-through or something, should I keep idling or shut my engine off to save fuel? I'm there for usually about 2 or 3 minutes at a time... depending if there's a line or not. I heard from a few people that cars use a considerable amount of fuel to start. What's the "cut-off" time? Meaning how long would the car have to idle to make it worthwhile to shut off? And if it makes a difference, my truck is a 94 S15 Jimmy with the 4.3 Vortec CPI. Thanks!

 

A guy I work with did a study on this in university. He found that vehicles manufactured after 1985 don't use any more gas starting than the initial rev of the engine. Can you notice a difference in fuel consumption when you rev your engine once? That was his outlook on it, and I trust him.

 

why do you think hybrids shut off?

idling= 0mpg
shutoff=infinite mpg (your not going anywhere and your not consuming any fuel)

 

I always find i Use very little gas just idling. I had put in enough for a half tank the other day and had done some daily driving, then encountered my tranny problem, so since then i had only been idling it in the drive way. The needle hasnt seemed to move much really

 

I was told by my old auto teacher that its better to shut your engine off if you plan on idiling for more than 5 minutes, otherwise leave it running beacuse it will consume more gas trying to start up. He just retired and he worked on mostly carberated vehicles in his life, so that "after 1985 thing" is probally correct, but this makes me think about modern vehicles and how after a few minutes they go into closed loop. For the minute or two until the o2 warms up (open loop), i would think that their would be alot more fuel consumption as opposed to closed loop, so maybe it was 5 minutes with carberuated cars, but do you really use 2 minutes gas on start up as you do waiting for the car to go into closed loop? Probally not so i would say shut it down to save fuel, but thats just what i think.

 

True but I didn't even consider that since hybrids are quite a bit newer than my Jimmy and they have tiny 3-4 cylinder engines (well, at least most of them do). But thanks for the help guys! I guess if I'm gonna gonna be sitting for more than a few minutes I'll just shut 'er down.

 

Considering the wear and tear on the ignition switch and starter coupled with the minuscule fuel consumption when idling, I would just leave it running.

If I wanted to dig around enough, I'm sure I could find the article I read a while back about a study done by a NYC cab company on this very topic. IIRC, they concluded that it was better for their equipment to leave things running unless they were actually parked.

 

Oh yeah, I forgot to ask about wear-and-tear too. Makes sense.

 

Considering the already somewhat weak ignition switch in these trucks... You don't want to start it more than you have to.