It's not only unsafe to coast with your engine off, it's illegal.
I really enjoy your column, and have learned a lot over many years reading it. I have a 1992 Toyota Tercel with a standard transmission. I am on social security, so I'm trying to save every penny I can. I spend most of the year in rural Georgia, with a lot of hills. So at first, I was coasting down the hills in Neutral with the engine on, thinking that might save some money over the years. Now, I am turning off the engine, and then putting the car in the appropriate gear to restart it later on. I can travel two to three miles several times going to town this way. Am I ruining any mechanical parts by doing this? And is it worth the little bit I'm saving?
TOM: Gee. You really are a world-class cheapskate, aren't you, Roberto? A man after my own heart.
RAY: Here's my calculation: This car gets about 40 miles to the gallon. So if you coast two miles with the engine off, you're saving 2/40ths of a gallon, or about a nickle.
TOM: But when the engine is off, you're in danger because you don't have any power brakes. Plus, one of these days when you shut off the engine, you're going to turn the key too far and get it into the "lock" position and lock the steering wheel.
RAY: Then you're going to plow into one of those roadside-boiled-peanut vendors, and he's going to sue you for five million dollars, which will more than wipe out the three bucks you saved by coasting.
TOM: Besides, I'm sure what you're doing is illegal. In fact, it's even illegal in most states to roll down a hill in Neutral with the engine ON! Even with the engine on, the car could stall, and you could lose your power brakes and power steering and never know it until you needed to stop or turn.
RAY: So I'd stay in fifth gear and look for a safer way to save a few pennies. You can start by writing shorter letters, Roberto. Then you can use postcards, and save 10 cents on every stamp.