How much gas does a fuel injected vehicle consume at idle? I have a 1995 Jeep 6 cyl. four liter engine. I sometimes run an inverter for AC electric.
There is no simple answer. It will depend on the vehicle. You’d have to measure it to determine the rate of consumption per hour for your engine.
About a gallon an hour will be pretty close. Maybe a little more if there is a slight load on the engine, say 1.5 gallons/hr.
If you were driving, at 60 mph, and your car got 30 miles per gallon, that would be 2 gallons in one hour, wouldn’t it? Just to ballpark (BIG ballpark) that, at idle, your engine would use 1/2, or 1/3, or 1/4 that. That would be 1 gal, or 2/3 gal, or 1/2 gal. One would need a flow-rate meter, or actually run the engine for a number of hours, starting with a known quantity of fuel.
Don’t forget to add in the cost of wear on the engine. Idling for extended times is hard on an engine. Be sure to change you oil extra often at the very least.
ANOTHER good reason not to buy a used cop car.
I believe a very rough estimate is about 1/4 tank over 8 hours. So, assuming your Jeep has a 60 liter tank, you’d use 15 liters per 8 hours, or 1.875 liters per hour. So, 2 liters per hour, I would think would be a decent guess - it works out to 1/2 to 2/3 of a gallon per hour, depending on whether you use US or Imperial gallons.