Assuming you have a modern car built in the last 20 years or so that is fuel injected, it is almost *always* more fuel efficient to shut the car down. Back in the old days of carburetors, there were instances where shutting the engine off for a short time would cause (slightly) more fuel to be wasted than by leaving the engine running (esp. when cold). But fuel injection shuts off fuel flow immediately upon turning off the key. Or, buy a hybrid and it doesn't use fuel when stopped unless your running the air conditioning on "HIGH"....:-D...

Just so you know, UPS "tells" all their drivers to turn their trucks off, even if they just stop at a house for a minute. Someone already did the homework!

You should never let your car idle for more than 30 seconds unless stopped in traffic or at a light. Not to mention (where I live) if you leave your car on and go into a store and your car gets stolen, you'll get a ticket.

leaving your car idle period is not a very good idea. I am a chem lab technologist and I test oil for heavy machinery. Occasionally I have tested the oil on my own car. My test results conclude that there was fuel in my oil. This is because my car was sitting idle from warming up during the winter months. Not only does this change the viscosity of the oil but it changes the composition of the oil. Don't let your car sit idle, if you are running into the store, turn it off.

You most definitely use more fuel when letting you car sit in idle while running into a store because a car doesn't use any extra fuel upon start-up. Other factors that are important should be considered: Most people stay in a store much longer than they anticipate, which would cause and even greater fuel use. If you leave your car running in the wrong place, it could run completely out of gas... because it will be stolen.

Turn it off, unless it is very cold. In theory, you could even turn off at a red light, if it goes red in front of you so you have the full cycle to wait.

No brainer, engines use more gas(or diesel)running than not running. dono

This day and age shut your vehicle of and make sure it's locked up as well..You wouldn't have to worry about gas while there is theives around... That would be my worry.lol

My question would be if you were waitng in your car because it was cold and had the heat on. Would being in idle burn more gas than if you were driving it?

That's a 'no-brainer'. A vehicle uses less fuel when it is not running. TURN IT OFF. As a 35 year veteran of the trucking industry, I cannot count the number of lectures and training sessions I've sat through where they tell you how much engine idling costs. (They make the analagy with a fleet of 500 vehicle which idles 10 minutes a day = $$$$$$$.) It's true what they're saying though.

It depends whether you want to save your fuel or your starter and the wear and tear from constant starting and shutting off.

It saves you gas by letting it idle...if you have fuel injection. your car has three sensors...idle, normal speed, highway speed and adjusts the injection nozels accordingly. Your gas pedal is really an "air pedal" by pressing your accelorator you open the airway sending more air to the fuel air mix causing a bigger explosion -combustion- in your engine..because you delievered more air your vehicle also needs slightly more fuel. by idling instead of turning your car off not only are you saving fuel but your not burning your starter, putting wear and tear on your engine...you see when your car is off the oil leaves the engine compartment and pools down in the oil pan. once you go to start your car your engine has to cycle a few times before the oil is circulated through your engine once again lubricating the parts. When you initially start your car the air intake sucks in a huge amount of air (and extra fuel) to initially get your engine going and then it settles into idle....so by turning your car off and on in a short amount of time not only do you experience more wear and tear but you use more fuel in a simple application. let your car idle if your only going to be gone less than 20 min.

A mechanic told me once that the general rule of thumb is: for every 2 minutes of idling, you can go 8 miles. Also, no matter what you drive, idling is hard on the engine.

With todays fuel injected engines, you should always follow the 10 second rule. If you are idling more than 10 seconds, it makes common sense to turn off the engine. The engine uses 10 seconds worth of fuel on start up. that's it. In EXTREMELY cold weather, its a good idea to sit in the car and let the engine run for 1-2 minutes before you drive. ( I am talking bone chilling cold, which is usually only a couple days a year in the north) THe sad fact is our wasteful habits of driving gas guzzlers, SUV's and leaving engines running is causing alot of the freak storms, hurricanes, floods, droughts etc. I remember a picture of a couple guys in Pickup trucks idling after Katrina hit, crying that they lost everything, oblivious that they and a million other idling folk were part of the problem. Buy a hybrid or a small car; only use the engine for what its intended to do...for transportation - not parking. Realize your exhaust pipe can fill a garbage bag up in seconds. With that image, imagine how many garbage bags worth of pollution your car emits as you drive. That image got me to stop unnecessary pollution when my kid brought home that image from school. Do it for the kids folks!

it depends on how long the car will be running. 3-4 min let it run any longer than that turn it off because you do use more gas to start the vehicle than to keep it running.

The amount of fuel you will save is trivial compared to the cost of frequently replacing and all components associated with starting an engine. Leave it run. It can also be a road hazard for you and others to shut off an engine at a red light. Those familiar with Click and Clack, know they say to leave the car run. They are MIT Grads and know what they are talking about.

I'd worry more about leaving the keys in an unlocked car.

generally in newer cars ifs its going to be idling for more than 30 seconds its best to turn it off however if you turn on and off a lot it puts unnecessary wear and tear on the sterter

generally in newer cars ifs its going to be idling for more than 30 seconds its best to turn it off however if you turn on and off a lot it puts unnecessary wear and tear on the starter

You should never leave a car running if the driver is not in the car. If the gauges started showing a problem and your not there to shut it off you could have a major problem.