Just a quick one for those who are more versed in car mechanics than I am…
Say you go to the bank to get some cash so you and your signifigant other can go eat breakfast one morning: now in the interest of conserving gasoline, should you leave your engine running while you run into the bank (provided that you actually drove a gas-burning vehicle), or should you turn it off for the 120 seconds it takes to get your cash?
I have heard as recently as this morning from my signifigant other that leaving the car running will conserve gas; this is from an undocumented expert I am not capable of cross-examining. Lots of people do this, foolishly, at that, while they run into establishments to run quick errands, leaving their vehicles unattended. I disagree, and think it’s best to turn off your car, because how could simply starting your engine burn more gas than leaving it running? Doesn’t idling an engine mean it runs at almost a 1:1 fuel/air ratio? I think that it is actually wasting gas to leave that sucker running.
I know that several of you out there know the answer to this, so please don’t hesitate, it’s just a quickie. Thanks.
Most organizations including the EPA encourage you to turn your vehicle off if
A) the idling will meet or exceed 30 seconds and
B) you can do so without presenting any hazard to yourself or others.
Some people have said 10 seconds for part A of this argument, but to me that sounds like overkill.
In the days of carburetors, the engine ran really rich on idle, and it was even more wasteful to leave it running. Now, the computer-controlled injectors waft in just enough gas to keep it ticking over. Still, you use less gas by shutting the engine off while you wait on your supersized superfree fries.
On the other hand, every start uses up one of your starter’s starts. So, you’re balancing gasoline pennies against starter replacement pennies.
And, by the way, if you’re in a big rig (heavy truck, bus, etc.), in many places (Massachusetts, for one) it is not only wasteful but illegal to leave it idling for more than five minutes. This is an air quality measure.
In addition to the fuel consumption issues, there are a couple of other factors to consider:
Leaving your car running unattended while you run into the store is an open invitation to car thieves.
If your cooling system is not in tip-top shape, idling for extended periods can cause the engine to overheat without the forced air flow provided by the motion of the car.
A car engine does require more fuel to start than it does to just idle, so for some period of time, it does save fuel to leave the engine idle rather than shut it off and restart it. It’s going to vary from car to car, but the number I’ve heard most is that the break even point is about 30 seconds. In other words, if you stop your car and start it 30 seconds later you will use almost exactly the same amount of gas had you left it idle for 30 seconds. If you leave it idle for any longer than 30 seconds then you are wasting gas.
“And, by the way, if you’re in a big rig (heavy truck, bus, etc.), in many places (Massachusetts, for one) it is not only wasteful but illegal to leave it idling for more than five minutes. This is an air quality measure.”
Air quality is an interesting aspect to this issue. During the time I was I taking an internal combustion engines class at U of MN in Minneapolis, the city was considering an ordinance to limit the allowable idle time for large vehicles also (I don’t know if it became law). The idea was that all the diesel engine delivery trucks left idling during deliveries downtown were causing air quality problems. The professor teaching the class sneered at this solution indicating that forcing the drivers to turn off their truck engines would allow the engines to cool off such that upon restarting, the engine would spew many times the emissions than it would have emitted if it had remained idling.