Shutting off the engine frequently to save gas: good or bad idea?

Dear Car Talk

Dear Car Talk | Jun 01, 2004

Dear Tom and Ray:

I seem to recall arguments going back to the original oil embargo about whether it's good or bad to shut off the engine frequently to save gas. I remember people saying it's bad for the engine. That makes me wonder about the new hybrid cars. Hybrid engines stop and start on their own all the time. Does this raise concerns about engine longevity? Is there a greater chance of long-term engine damage from all the stopping and starting that a hybrid engine does? -- Paul

TOM: No. When a hybrid engine shuts itself off at a stoplight and then restarts itself, no damage is done to the engine. In fact, if you do this yourself in a nonhybrid car, you can even produce some tangible benefits.

RAY: For the engine?

TOM: No, for your right wrist and forearm. You'll really build up those key-turning muscles.

RAY: In the old days, when cars were carbureted, there was some truth to the warning against restarting frequently. Because carburetors were so imprecise, they'd essentially dump gasoline into the cylinders whenever you started the car. And some of that gasoline would wash down the cylinder walls, rinsing off the crucial film of oil on there. Then that mixture of gasoline and oil would seep down into the crankcase, diluting the engine oil even further.

TOM: So if you started a carbureted car frequently, oil dilution was a real problem. But these days, with fuel injection, only the exact amount of fuel you need is sent into the cylinders, so there's no wash-down or oil dilution, no matter how often you start the car.

RAY: So, the only parts that get additional wear and tear from starting the car are the starter and battery. But the effect on the life of the battery will be minimal, because the restarts always occur with a warm engine, which is easy to start. And at least in Toyota's hybrid system, there IS no starter motor, per se. The hybrid's electric motor itself serves as the starter motor. And that's not going to wear out (or at least we hope not!).

TOM: So you CAN save fuel by shutting off your engine. Hybrids are designed to take advantage of that savings. And if you don't have a hybrid, you can do it yourself. Personally, I think it's inconvenient to shut off the car at every stoplight. But if yougoing to be stopped for more than a minute or two, you will save fuel and won't do any damage to the engine.

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