Fuel Economy

During the gas crunch of the mid 70’s, there was much discussion regarding the advantages and disadvantages of shutting off the car while waiting for a stoplight, train, etc. Is there a rule of thumb for how long a wait would warrant turning of the engine to save gas, versus the amount of extra gas it would take to restart the engine?

Once your car’s warmed up, it takes practically no extra fuel to restart the engine. But on the other hand, compulsively turning the engine off and on will drastically shorten the life of the starter and the amount of fuel a modern engine uses at idle is pretty minuscule, so unless it looks like it’s going to be a long train, you’re probably better off leaving it running. Shutting the engine off at a stoplight is unsafe and uncourteous to other drivers.

If the wait is a long one, over 3 minutes, you can save some fuel by shutting off the engine. But the starters used in most cars are not designed for that kind of service. They only last so many “cycles”…

GreasyJack’s right about it not taking much gas to restart the engine and the wear on the starter. I just want to add that I shut my car off for trains or if I’m waiting for someone, but not in traffic. I don’t at stoplights because the delay could anger other drivers or I could cause an accident for a variety of reasons, like because my brake lights aren’t on or it takes too long to get moving.

It DOES NOT take extra gas to restart a warmed-up engine. You will always save gas by shutting off the engine.

I don’t shut off my engine in normal traffic, but if I were stopped for a train or a crash, or something I thought would take a few minutes, I’d shut it off.

Cars were carburated in the '70s. Nothing from that era applies.

As others have said, it saves a small amount of gas (tiny) but adds wear to your starter. IF you live in an urban area you could be multiplying the amount of cycles your starter has to perform by many times and shortening its life considerably.

I also agree with Hoffmair’s statement about the safety. When the light turns green, everyone behind you wants to go. Nobody wants to sit and wait for all the “green” people to start their engines. And there are a lot of unstable people out there. Do that and you’ll be increasing the number of pissed off nuts we all have to share the roads with.

I recommend against it. Mainly for the last reason mentioned.