here you go--
I read somewhere the average V8 motor uses between 1 to 2 gallons an hour idling.(some book I read about geting maximum MPG's)...naturally smaller engines will consume less,and EFI will not use as much as a carbed motor,mostly because they don't use a choke,and atomize the fuel more effeciently,especially when cold,when a carb is at a disadvantage..
At any rate,it IS a waste of fuel if the motor is running,and the vehicle isn't moving..unless you'll die of frostbite on a night like tonight is here (5 degrees!)..I hate being stuck in traffic jams or at red lights..I can see the $$$$ signs on the gas pump spinning while I'm going nowhere!.
I often run my vehicles out of gas if they are just going to sit..I'll dump in a gallon of gas and start them up once in a while to keep the battery charged and the motor free..I can run my 307 in the van about 20-30 minutes on a gallon of gas if its cool out..a bit longer in the summer..
I had a 454 in a 74 C10 years ago..that thing would only run about 10-15 minutes on a gallon of gas..

..those Holley carbs are toilets!..another I had with a Q-jet wasn't much better..the choke wastes a lot of gas..especially automatic chokes that usually stay closed longer than nessasary..
Some newer vehicles must not use too much..I heard about a Jeep Cherokee in a neighbors yard last winter ,that had a remote starter,and guys plowing the parking lot in the Toyota dealership unknowingly started the jeep up too,when they hit the remote starter on a used Ford Escort they had to move in order to plow(must have been on the same "frequency!")..it ran all night and until 3pm the next day,until someone at the apartment called the cops to complain it had been running since 1 am the night before!..and it still had about 1/4 of a tank left...
My diesel VW Jetta would go 600+ miles on a tank of 14 gallons..so that thing would probably have run a week or more if it had a full tank,and I forgot to shut it off!...

..wish I kept that car...
