Idling 30 seconds vs cranking

Factual Questions
1

I’ve heard that the “average” car uses as much gas cranking as it does in 30 seconds of idling. So, if you’re stuck in traffic, and you think you won’t be moving for at least 30 seconds, you’re better cutting off your engine. Less than than, and you might as well leave it running.

How accurate?

2

Well, I won’t touch the fuel argument but you probably have a point if you just look at that. However, more importantly if you shut off your engine, all of your oil drains to the oilpan. So, when you start it all that oil has to get pumped back up and start lubricating again. You may burn a bit more fuel (maybe) however, the wear and tear you save on your engine by keeping it running is more important. The first few seconds an engine is running when it is started (I saw this somewhere, don’t ask me to back it up :wink: ) account for more than 50% of the total wear of an engine. In other words, the first 3 or 4 seconds your engine is running (until oil pressure builds) you engine has had more wear than the next 5 or so hours it is running…or something like that :slight_smile:

Eric

3

The large amount of wear and tear on the engine when first started, due to the oil having drained into the oil pan, probably isn’t relevant if you’ve just stopped your engine for a minute or two. I doubt your oil has all drained into the pan, so your engine is still lubricated.

4

not to mention the wear on battery and starting motor. They are designed for infrequent use.

5

Oil at operating temperature is very thin, and will drain into the pan very quickly. I would say that for the purpose of this discussion, yes, it would be in the pan after a minute or two. Sure, there may be a cup or two distributed in the galleries and laying in low spots in the head but they are not going to make any real difference. My best guess from personal experience would probably be more in the realm of seconds (10-20?) before the vast majority of oil is back in the pan. For an experiment, try pouring hot oil that you just drained from your engine if you are changing it back in. I would bet money that it would flowing out almost as fast as you pour it in.