How long engine should be off
 

When stoped any where i try to turn off my car. Ive read somwhere that it usally takes 7 seconds of gas to restart it. I havent seen much differance in MPG at all. I coast a lot with the engine off at least one time a day for about 2.5 miles. So is that 7sec realalistic or is that being to optimistic

I've heard five seconds, and seven seems just as reasonable. For the second or so the injectors start firing on start up, they dump in a lot of fuel, but not so much that you won't see an improvement from coasting 2.5 miles with the engine off. Otoh, since you're driving an automatic, I suggest coasting with the engine idling in N because if the engine is off, your transmission probably isn't be properly lubed. Not that it'll instantly explode if the engine driven oil pump stops pumping, just that certain bearings may start wearing much faster. You'll see an increase in mileage, w/o as much wear on your transmission.

This is the main reason for bump starting your engine, and if you can at home, park on a hill to alow you to alwas bump start it, thus preventing that extra bit of fuel from being used up.

Does bump-starting use less fuel than key-starting? Does anyone know how much less?

Perhaps, but at the expense of your clutch. Trade-offs. Its all about trade-offs.

And probably wear rates as well. A starter will spin the engine relatively slowly and take a second or so to catch, allowing some oil to get pumped up to the head, but when bump starting your dragging the engine up to 1-2k rpm much faster, so if it's done on a cold vehicle, there isn't as much oil where it should be.

I thought if you coast in N with the car on its bad for it. I coast with it in N with the car off.ALso i have a auto in case that matters

With an automatic, if you are going to coast in neutral, leave the engine running. In most auto trannies, this is the only way that the oil gets circulated through the transmission (oil pump is driven from the engine input). The output shaft bearings and seals should have lubrication while they are spinning.

Oh yeah, I am pretty sure that is illegal in most states to coast in N with the car moving (engine on OR off).

Personally I prefer to leave the tranny in D and touch the throttle just a scutch.

-Bob C.

how could the cops or anyone for that matter prove you were in neutral as opposed to slowing down?