on the 2-05 show a woman called about her husband coasting down a mountain. the guys did not hit on the most important point. if the coaster leaves the car in gear, during deceleration [coasting], the fuel injection computer turns off the injectors. the engine is just passing air through. mileage is infinate
in high gear, if the car was slowing too fast, maybe this is why the coaster shifts into neutral.
Using any gear while coasting will give you the same effect, injectors turned off. So, you can go to a lower gear to use engine braking to maintain speed on the downgrade, and save the brakes for when you really need to slow down. Brake fade is very common on the down grade when drivers don’t know how to use the engine to keep speed.
Shifting to neutral is the worst thing to do, the engine is fed fuel to maintain idle, and only the brakes are slowing you down. When they burn up or fade…
Just ask a trucker.
Coasting down a mountain in neutral is akin to a death wish. That’s why it’s illegal to do so in a lot of states.