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I was sitting outside, eating my lunch the other day, and a small bus (you know, one of the short ones) pulled up to the sandwich shop I was eating at. I noticed that the driver got out of the bus, ordered her food and waited for the roughly 10 minutes until the she received her sandwich and then proceeded back to the bus and ate her sandwich, all the while the bus was still idling the entire time!

My natural assumption is that this is a HUGE waste of gas, and thus prompted the thought "Why?!". So my question is this, are there any distinct advantages to idling a vehicle over shutting it off, and then starting it back up again? If so, is there a general 'time limit' for idling the vehicle?

James Mertz
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Assuming the bus has a diesel motor, the answer is yes. As an old German Mercedes mechanic told me, "with a gas engine, the primary contributor to wear is hours of operation but with a diesel it is the number of times it is started".

What that really means is not the number of times you engage the starter motor but the number of times the motor is heat cycled. To support that idea, when I lived in Olympia, Washington there was a diesel logomotive that was used for moving cars in a small switch yard. I seldom saw the locomotive in use but it just sat there at idle 24/7.

Phil Hughes
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I think this is going to be completely personal opinion. If it is less than 40F outside, I will go out 15-20 minutes before i need to leave in the mornings and let my truck idle, to warm up the block but also to warm up the cab so I'm not freezing while driving. When the summer rolls around and its over 110F and I will not be out of the truck for more than 20 minutes, I let it idle and keep the air running. Now does this waste fuel? To some I'm sure it does but it does not to me. The old diesel motors, before all this EPA crap was put on, could idle all day and all night and it wouldn't hurt the motor at all. Gas motors it isn't great to idle it, but also I have never heard of anything major happen that was solely based on idling a gas motor. But again I think its all based on personal preference. I know people that will idle their truck while they are in the grocery store for 2 hours, I also know people that turn their truck off even if their just checking their mailbox for 2 minutes.

Zencyl
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Remember that there may have been other specifics in this case that made it a special case. Maybe the battery had just been replaced or discharged and had to be jump started, and so they were trying to build up a charge? Maybe that particular bus was having mechanical issues that caused it to sometimes be particularly hard to start? Maybe they needed to warm the engine up for a oil change or emissions test?

Sean Reifschneider
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I just read at the Environmental Defense Fund site that idling 10 seconds wastes more gas and is harder on the engine than turning off and restarting. Specifically, for BOTH gas and diesel vehicles.

Plus that exhaust increases the risk for you and the community, for bronchitis, heart disease, cancer - and specially asthma in kids.

Not to mention, the petroleum industry loves how much money they make off the millions of gallons of gas American idlers waste.

And of course, some 99‰ of climate scientists agree that climate change is being caused by human behavior.

The only ones who disagree work for the petroleum industry, etc., who profit massively from said human activities.

user23901
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