I start and stop a lot, waiting to pick up people and the like. Would it be better for the engine to idle for 5 mins or shut off the engine for 5 and restart. I'm not sure which is the lesser of two evils here or if it'd make a big difference. Any thoughts? What about even shorter lengths of time like 3 mins? 10 mins?

 

This is a "gut" reaction but I'd say under 5 minutes leave it running; over 5, shut it off.

 

I've always heard it's better to let your car idle for a few minutes then to keep starting. The cats stay warm and do their job when you let the car idle.

 

I agree, probably best to leave your car running.

This car company (very big huge company) that I used to work for was developing this engine that was specifically designed to start and stop a million times a day. Maybe a million is exaggerating, but this is what they were trying to accomplish:

When you're driving in traffic, you waste a lot of gas because you're constantly accelerating and then decelerating. The engine was supposed to "shut off" when you take your foot off the gas peddle and "start up" when you put your foot back on. Logically you save gas because your engines not running when you're just sitting around or when your decelerating.

It was supposed to be so seemless that you wouldn't even notice the engine was off or on. And of course it was supposed to happen a million times a day.

Anyways, thats the future. Of course the hydrogen fuel cells they're starting to put on the roads are really exciting.

 

I believe one of the dominant engine life factors is still the number of thermal cycles an engine eperiences. In other words for every shut down/start up cycle the engine experiences a large thermal stress cycle that adds to the engine degradation. Of course, this is weighed against wearout parts and mechanical stressed parts, .... I'm not sure how engine designers make that trade these days.

My preference is let it idle for a few if I know I will be moving momentarily.

 

definetly leave it running. i think it would be easier on the cats and the engine.

 

what might the cut off time be for idleing....like 10 minutes or somthing like that?

Nathan