Does turning your car off and on waste more gas than idling?
No, not for a modern engine. Restarting burns about 10 seconds worth of fuel, per the EPA, while a stalled engine at idle keeps burning fuel the whole time it sits. Past about a minute of sitting still, shutting off wins.
Why the old rule doesn't hold anymore
1. Restarting used to flood the carburetorOlder carbureted engines dumped extra fuel on startup, so shutting off and on really did cost more. Fuel injection replaced that decades ago; a modern engine restarts on a precisely metered squirt.
2. Idling just keeps burning, with nothing to show for itAn idling engine is running the same combustion cycle as driving, at zero miles per gallon. Every minute it sits there is fuel spent on nothing.
3. The break-even is short, about a minuteTen seconds of restart fuel versus a quarter to half gallon an hour of idling means the trade flips fast. Past roughly a minute of sitting still, the engine that's off is the cheaper one.
What idling actually costs
| Situation | Fuel used | Cost* |
|---|---|---|
| Restarting the engine | about 10 seconds worth | next to nothing |
| Idling, AC off | ¼ to ½ gal/hr | about $0.01-$0.02/min |
| Idling, AC on | ¼ to ½ gal/hr, more with AC load | about $0.02-$0.03/min |
| 10 min/day avoidable idling, a year | roughly 12-25 gal | about $44 to $88/yr |
*Per-minute figures and the 10-second restart estimate are the EPA's own (fueleconomy.gov). The yearly figure assumes 10 minutes a day of avoidable idling (school pickup lines, drive-thrus, waiting on someone) over 300 days at $3.50/gallon.
When to actually shut it off
- Longer than about a minute, turn it off. A train, a long drive-thru line, waiting in a parking lot.
- Short stops, leave it running. A quick red light or pulling up to a curb for a few seconds isn't worth the fuss, and the fuel difference is tiny either way.
- Warming up the engine doesn't need idling. Modern engines warm up faster being driven gently than sitting in the driveway.
- A car with stop-start already does this automatically at every light, which is exactly the same trade playing out thousands of times a year with no wear problem.
Questions people ask
Does turning your car off and on waste more gas than idling?
No, not for a modern engine. Restarting uses about 10 seconds worth of fuel, per the EPA. Idling burns a quarter to a half gallon an hour. Any stop longer than about a minute, shutting off saves fuel.
How much gas does idling actually use?
About a quarter to a half gallon per hour, depending on engine size and whether the AC is running, per the EPA.
Is there a rule for when to just turn the car off?
Yes. If a stop will run longer than about a minute, a parking lot, a train, a long drive-thru line, turn the engine off. Shorter than that, restarting costs about as much fuel as idling would have.
Does this wear out the starter faster?
Modern starters and batteries are built for this; it is the same system stop-start cars use every time they sit at a light. Normal city driving does not wear one out meaningfully faster.
Every default and its source: Methods.