Join the Car Talk Community!

Discussion Rules

Welcome to the Car Talk Community!

Want to ask a question or join the discussion? Great! Join now.

Sign In Register

Does turning off engine at red lights save gasoline?

So there's this annoying red light on my way to work. When the light turns red, it is one minute and twenty seconds until it turns green again (I timed it). So if I am the first or second person at the light, I put the car in neutral and turn off the ignition.
<br/> Will this in fact save any gas? Are there any other downsides to doing this? My wife claims it's dangerous (it is not a dangerous neighborhood).
<br/> So am I saving any gas, or am I taking this "green" thing too far?
<br/> Thanks in advance,
<br/> -- Mark


  • edited March 2010
    Down sides.
    1. You annoy me when you don't get moving quickly when the light changes.
    2. Added wear on your starter, battery, and alternator.
    3. Spousal discontent.

    Saving gas?
    Probably not. It takes more gas to start an engine than while it is running. It will also have to work a little harder to recharge the battery. Clearly, there is some break even point for your specific car where the overall gas consumption will be less, and it is dependent on how long the engine is off. I don't know where that point is, and it might be as little as the one minute that you are stopped.

  • edited March 2010
    Hey Mark,

    Well the potential fuel savings are off-set by the disadvantages that tardis mentioned. It's rare for me to even put my car in park, such as while waiting for a train to pass and it's more rare than a blue moon for me to feel compelled to shut down the engine. Maybe I will if the thing is just barely crawling along, but again, it's rare.

    I used to have a pizza gig and I would almost always leave the engine running while at the customer's front door.

    Doing regular preventative maintenance on your car will go a much longer way toward being green.

    Hope that helps.
  • edited March 2010
    If we were talking about a car from the 1970s with a carburetor, there would be no fuel savings from shutting it off for 120 seconds. However, with today's fuel injected cars, if you are going to leave it on for more than 60 seconds, you can save fuel by shutting it off. However, saving fuel shouldn't be your only concern.

    How much fuel will you save? I don't know. Is it worth the extra wear and tear on your starter? Not in my opinion.

    Think about carjacking. If you are first in line, and your car is approached by a carjacker, you have the option of running the red light, but only if your car is already running. Even if you are not first in line, having the car running might allow you to escape faster.

    At truck driving school and the Motorcycle Safety Foundation's Basic Rider's Course, we were taught there is a remote chance that being in gear ready to go can give you a safety advantage. Even if the chances of you reaping any benefit are remote, I think it is still a good idea to leave it running.

    If you are so obsessed about saving fuel, buy a moped.
  • edited March 2010
    With a modern engine the break even point for leaving the engine running vs. shutting it off and restarting is less than 20 seconds,.
  • edited March 2010
    Yes, it saves fuel. That's why some hybrid vehicles shut off their engines while at rest. I don't think it's dangerous. I believe this is common practice in parts of Europe where fuel is expensive.

    It doesn't save a lot of gas, but every little bit helps.
  • edited March 2010
    Those hybrids also have special starters that are more robust than normal starters, so they can stand up to the extra use.
  • edited March 2010
    It saves an amount too small to measure, but IMHO it truely is not worth the added wear on the starting system. McP correctly pointed out that hybrids do this, but their starters are designed to survive routine cyling to a greater extent than yours is.

    But unless you live in an urban area, where slow starting from a light can earn you a crowbar on the skull, it isn't dangerous. Much of the difference in the responses you'll get is truely philosophical. Some feel that every drop saved is important, some do not. I'm in the latter group.
  • edited March 2010
    Yes it does, depending on how long.
    Unless you have a golf cart or hybrid that was designed for it, it isn't worth it to shut down unless for it's for extended waits .
    Yes it may be dangerous in some situations as you can imagine.
    So bottom line, like in most discussions, there are different sides when you look at ALL the factors involved including length of time and technology in your vehicle.
  • edited March 2010
    The extra wear and tear on the starter and iginiton switch will eat up any savings you might have from shutting off the engine at a red light.

    Like others, I shut the engine off when waiting for one of those long freight trains to pass.

    You may cause an accident by annoying drivers behind you who expect you to get moving as soon as the light changes.
  • edited March 2010
    While I won't turn the motor off at every stop light, some are ridiculously long. When I visit my son in Wilmington, NC I notice how long some of the lights take to turn. If I lived in Wilmington NC I likely would kill the motor on some known long lights.

    This seems to be the case here, a 1 min. 20 sec. light seems like a long time. My car restarts very quickly and I won't hold up the traffic behind me so in this case I go along with the OP and kill the motor.

    It definately saves thimble full of gas, but it adds up if done by lots of cars. I haven't replaced a starter in a long time so I'd risk the wear and tear on the starter to save some gas.

    Today I turned my car off at the drive up bank window, so it is something I'll probably be doing more often in the future.
This discussion has been closed.