Recently someone mentioned to me that they always turn their car off when stopped at a light because it saves gas. I’ve never heard of this before (in 40 years of driving). I guess it makes sense if the light is more than a couple of minutes, which isn’t unusual. But then, wouldn’t this put more stress on the starter, use more battery power and who knows what else?
Anyway. Have I been missing out on a gas saving technique all these years?
It’s a real way to save gas – enough that a few new cars do this automatically. Hybrids do, of course, but also a few cars with ordinary engines. But those cars do have starters and batteries engineered for much heavier duty.
The savings won’t be huge, but in heavy city traffic it might cut fuel consumption by five or ten percent (~ a few mpg).
My Insight hybrid sometimes automatically shuts off the engine when I stop (at a light or whatever) then starts up when I take my foot off of the brake, but it’s designed for that and I’m not sure that I’d recommend it for a plain old internal combustion engine.
For one thing, it seems like you might be holding up traffic while you restart the engine. I also have to wonder if you’d drain the battery if you do a lot of city driving.
You also have to consider the added wear on the starter and associated parts.
This site claims that idling 30 minutes per day will piss away a tank of gas in two months’ time. Granted, that’s a lot of idle time; my car often only runs for a total of 30 minutes per day, with a tiny fraction of that being idle time. But if someone is letting their car idle for a long time to warm it up, and then spending a lot of time driving in the city with lots of stop lights, I suppose the potential is there for a lot of idling time where fuel could be saved by shutting the engine off.
Yes, it’s more wear and tear on the starter - but I’ve been through three cars now without having had to replace a starter, so they’re fairly durable. I understand that UPS and FedEx delivery trucks go through starters at a ridiculous rate - but then they may make a 100 delivery stops in a single shift.
It works if you do it right. I had a '66 VW that would start with just a bump of the starter. I once was nearly out of gas with payday two days away. Doing the stop the engine at stoplight thing let me get through 'til payday.
Actually a light that is red for a couple of minutes is very unusual. Someday when you’re stopped at a red light that you consider a long one in your area actually time it. I bet you’ll find that once it gets past 30 seconds, you’re beginning to think it’s a long light. I don’t think you’ll find too many that stay red for even 1 minute. There is only one near me that does so and it lasts about 1:15 but only when a pedestrian walk is included in the sequence.
There are two lights on my way to work that have over a 4 minute cycle. I’ve timed the red lights at 4 minutes, with about 15 seconds of green for my direction. It’s a major highway I need to cross. So, a yellow light means floor it because you won’t get another chance for 4 minutes. But yeah, a minute or so is normal for most lights.
During the summer here, turning off the car at every at stoplight is not a workable plan. It takes long enough for a A/C to pump it down to a bearable temp without turning it off and rolling the windows down every few minutes.
Back in the days of carburetors, they used to say one start up equaled 3 minutes of idling. I’m sure that has changed some with the modern computer controlled cars.
I would never shut off my engine at a traffic light, regardless of what it saved. What if something happens and you need to instantly move your car? You’re SOL in that case. I understand that some of the new cars do turn off the engine during periods of inactivity, however, I believe that they instantly start the motor when the gas pedal is pressed.
I’ve read that technique can cause lots of stress on engines which have not been designed for it. They may save a few pennies in gas, but they’re risking expensive engine repairs down the line. I would expect the starter and battery to fail sooner than normal.
Plus, there’s always the chance the engine won’t start and they’re now stuck in the intersection.
Only at lights I’m familiar with that I know have a long cycle. You can generally see the cross traffic light, so when it turns yellow, I fire my car back up. That way I’m not holding up people behind me.
For modern cars, at least, the excess wear and tear on the engine may be nearly negligible.
Apparently, the breakeven point may be as low as 10 seconds. Of course, it’s still usually a bad idea because it’s illegal in many jurisdictions and you want to be able to react quickly in an emergency.
They start when you release the brakes. At least that’s how mine works. Waiting for the gas pedal to be pressed would make a problem that occurs on hills even worse.
If I’m stopped facing uphill on a slope, when I release the brake, the engine starts quickly, but not quite quickly enough to prevent me from rolling back a slight distance. If someone is stopped too close behind me, I could roll into them.
The answer in this situation is to let up on the brakes just enough so that the engine starts then quickly reapply them till it’s up to speed and I can safely move my foot to the accelerator.
Imagine this scenario if it didn’t start until you pressed the gas pedal. You’d be rolling backwards the entire time your foot was moving from the brakes to the gas.
It’s not just wear and tear on the starter and battery. When an engine starts, the engine is less lubricated since the oil pump wasn’t turning and distributing oil. There is also the small matter of heat after stopping the engine - since the water pump also stops turning, it can’t dissipate localized heat by distributing coolant.
Conventional engines just aren’t designed for frequent stops and starts. You may save gas in some situations, but it can come with a cost some place else.
They said the same thing about florescent lights. I’d have to see a reliable cite to believe that.
The issue about oil wouldn’t apply when stopping the engine for a stop light. The oil wouldn’t drain away that quickly. I’m not sure why the water pump would be an issue either. It’s doing the same thing it does when stopping any other time.
When I lived in California, there was a long light on my commute home, and I would stop the engine for that one. I don’t have any lights near me where I stop my engine, but I did recently cut my engine for a train. Restarting it seemed almost effortless, because it was warmed up. I’d have a hard time believing it was somehow equivalent to three minutes of idling.