# Does Idling the car save or burn gas?



## RamistThomist

I saw these gas tips on TV and one of them said that if you are going to have your car idling with the engine running for over a minute, then you would save more gas by turning it off.

Is that true? I always thought that turning it back on used up a good bit.


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## jfschultz

Draught Horse said:


> I saw these gas tips on TV and one of them said that if you are going to have your car idling with the engine running for over a minute, then you would save more gas by turning it off.
> 
> Is that true? I always thought that turning it back on used up a good bit.



It depends on how much gas is used idling compared to starting the engine. The modern fuel injection engine uses less gas to start than was the case before.

But there is a down side to this suggestion. Most automotive engines use the crankshaft to drive the oil pump. Though the starter will spin the engine fast enough to start (about 100 RPM), it is not fast enough to bring the oil pressure up. So the engine runs without sufficient oil pressure for a short time every time it starts.

Hybrids that automatically stop and start the engine avoid the oil pressure problem with a motor powerful enough to spin the engine up to idle speed or above to establish oil pressure before turning the engine on. (On a Toyota hybrid this is about 1000 RPM with valves held open to minimize stress on the engine.)


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## jawyman

I have always heard that you burn more petrol by turning the car over than allowing it to idle. I don't have any proof, but that is what I heard. And that is my  worth.


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## VictorBravo

jawyman said:


> I have always heard that you burn more petrol by turning the car over than allowing it to idle. I don't have any proof, but that is what I heard. And that is my  worth.



That may have been true with your 69' Oldsmobile and its 4 barrel carb, but with fuel injection these days, it's not. The oil pressure issue mentioned above, though, is a factor. All in all, though, I'd leave the car idling unless you were going to be stopped for more than 5-10 minutes, not 1. 

They don't contemplate that starters wear out and cost money too.


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