[toomuchtodo]

Assuming, for comparison, a V6 Toyota Highlander, approximately 0.5 – 0.7 gallons of gasoline burned per hour at idle, or 6 - 8.4 gallons of fuel burned in total. Fuel tank capacity is 17.9 gallons, so about 30%-50% would be consumed in 12 hours.

[beerandt]

But you don't need to idle the whole time.

As much as I hate the new autostop in cars, it's smart enough to turn the engine on just for heat generation.

The bigger issue is the growing number of vehicles that turn themselves off after 20 mins in park, engine running or not.