Driving & Driving Test Tips: Neutral to save gas - automatic transmission, 2007 honda odyssey, honda odyssey

Question
Don,
 I saw a previous response and I figured you might be able to help.  A friend of mine drives a car with an automatic transmission and a trip computer.  We both live in the Northeast.  He's told me he's able to get between 10% - 25% more miles per tank of gas by coasting in neutral whenever possible.  he's kept some detailed information that is quite compelling.  Despite having some concerns about the effect on the transmission, I decided to 'test' this on a recent trip.  To my surprise, I got 460 miles from one tank of gas from a fully loaded (3 adults, 2 kids, and stuff) 2007 Honda Odyssey.  I found there were numerous stretches of highway that I could coast for over a mile.  With 'normal' vehicle use, we were getting between 300 - 360 miles per tank in depending upon driving use.  Based on my personal test, I have to concur with my friend that there is some significant savings given the right road conditions and traffic, BUT I'm hesitant due to the unknown impact on the automatic transmission...The shifting involves putting the car back into drive while operating at highway speeds.  The engine rpms drop from ~2500 to ~800 while coasting, but as expected when returning to 'drive' the engine revs slightly higher and slows the vehicle slightly as the transmission engages.  
Your thoughts....

Answer
It is entirely possible the savings you are getting from doing this is coming from your desire to get better mileage.  SO you  are driving better ALL the time.  Probably comparing your mileage to some trips you took when you weren't paying attention so much.

Many modern cars cut almost all fuel, some cut all, when you coast in gear.  Going to Neutral for a few hundred feet isn't going to hurt the transmission much and when you go back in gear the rpm's are real low, so I doubt it is hurting anything, but I suspect if you do the test again, and only change NOT shifting to neutral (I assume also you are leaving the engine running, otherwise when you cut off the key, you will cut off the power steering and brakes!) and try your best to get good MPG.  You will probably do the same.

I will venture that you are probably putting a little more wear and tear on the tranny, but I don't claim to be an  automatic transmission specialist.

Be aware that coasting like that is illegal in most states.

Don