1996 Chevrolet Astro Owner's Manual - Page 160

Run your engine only as long as you must. This saves fuel. When you run the engine, make it go a little faster than just idle. That is, push the accelerator slightly. This uses less fuel for the heat that you get and it keeps the battery charged. You will need a well-charged battery to restart the vehicle, and possibly for signaling later on with your headlarnps. Let the heater run for awhile. Then, shut the engine off and close the window almost all the way to preserve the heat. Start the engihe again and repeat this only when you feel really uncomfortable from the cbld. But do it as little as possible. Preserve the fuel as long as you can. To help keep warm, you can get out of the vehicle and do some fairly vigorous exercises every half hour or so until help comes. 4-22