Coasting in neutral vs. coasting in 5th gear

mazda
mazda3

#1

I was coasting down Bullpasture Mountain the other day and my passenger Dan said I was making a mistake shifting to neutral instead of staying in 5th gear. He said I would burn the same amount of gas in 5th even though I would turn 2,000 rpm instead of 900 rpm because the computer shuts off fuel to the injectors. I disagree. Who’s right? (Let’s not talk about overheating brakes in this case - if I felt any brake fade I wouldn’t be coasting at all.)


#2

If your car is of recent vintage, like the last 10 years or so, then your passenger is correct.

Update: But as tardis noted below, it will be less gas in 5th and not the same amount of gas. I didn’t read the OP’s wording closely enough to see that wording.


#3

Actually, you would burn less gas in 5th than in neutral. In neutral, you burn gas to keep the engine idling. In 5th, you would burn no gas at all because gravity would keep the engine turning via the transmission.


#4

This is asked over and over and over here. Please search and you’ll find the answer.


#5

My car has an instant MPG readout. Judging the speed of instant MPG rise to the readout maximum of 99 MPG, coasting in neutral saves gas. Your car may be different.