PLus its got to be very annoying turning your car on and off every stoplight. NOt worth the extra mpg. If you want more mpg buy a civic.

 

That's an unfounded assumption too. Across the board, there would be tremendous variation. Cars like the Prius routinely shut off & restart their engines. They have to assure (through design) that it will start reliably, using less than ?X? seconds worth of fuel.

But for any random car, without knowing the make, model, year, air temperature, oil temperature,& especially the state of tune of the engine... It might be anywhere between 90 seconds to 10 minutes.

But still, I usually shut mine down if I'm stopped for a train. Not red lights.

 

Jim .... hybrid cars that shut down when they stop also don't use the starter to re-start. They use the tranny while driven by the electric motor. It's a much easier way to start the motor and saves gas. The gas motors on them are very weak also which saves gass further.

For those that really want to save gas at red lights, get a deisel. They can idle on almost no gas and in general get about 30% better MPG.

 

no one is mentioning that turning starting your car wastes the most gas of anything you can do. thats tons of gas that is wasted every start up.

EDIT:not TONS of gas, but it adds up.

 

It sounds high to me too but that's the number he threw out there so that's what I worked with. And as for starting your car wasting tons of gas that's not true anymore, they have found that with newer fuel injected vehicles shutting your car off for a period over 60 seconds and re-starting it uses less fuel than leaving it idle for 60 seconds. With older carbed cars this wasn't the case.

 

anyone remember 'bad idea jeans' from SNL?

 

the alternator always draws the same amount of power out the engine regardless of the load on the electrical system. electricity doesnt work like that, its not any harder to crank an alt when your using a lot of power from it. (unless there is some sort of device inside the alt itself than increases the friction/speed of the alternator when electrical load increases....)

EDIT: Nevermind, I did a little research and it increases power flow due to a circuit that can increase the magnetic field difference, thus increasing magnetic flow across the armture.