on newer cars the restart generally matches about 20-30 seconds of idle time. on older cars and gas hogs, it's generally more. Big rigs can take a hell of a lot of diesel to start which is why you'll see some of them left idling over night. it does actually save gas. but you have to know what your car is like to start. if it's a real bugger to crank and is a gas hog, leaving it running for 5 minutes may actually save gas. but if it's a breeze to start and sips gas, you should prolly cut it off if you're going to be idling for more than 30 seconds or a minute.

Also, it's a good idea to turn the AC off on older vehicles (especially those that don't have the newer rotary compressors) because if you don't manage to start the engine on the first crank and the engine rolls backwards some, it may damage the compressor. This is usually only a problem on carbureted engines or injected engines with rich fuel problems that can kick-back.

 

my car has done that before but i was having battery issues and my battery was dead and it would click like that after i turned it off... are you having trouble starting the car? you might have a bad battery...