Quote Originally Posted by jut703 View Post
Using the same car, in the same driving conditions, my mother garners 6.6-7.1 km/l. When my dad used the car for a week, his average was 8-9 km/l, and they both pass the Makati-Pasig route. This is despite the fact that he drives at an average speed 20 kph faster and has occasional bursts of boy racer tendencies.

I would attest the lower FC of my dad to the fact that he keeps a more constant and less hasty acceleration from standstill, but he also does one quirky thing - he frequently puts the car in Neutral when coasting.

Is this bad for the car? It's an Altis 2.0V A/T. Also, I've noticed that when taking the foot off the gas, the rev drops to 1000 rpm. Does that mean that even in D, when the pedal is disengaged, the car goes to neutral? In other words, is the act of shifting to N every time you coast unnecessary?

And, does shifting to N actually help improve fuel economy? If so, at what cost? Does it drastically increase the wear and tear of the transmission?

I'd just like to be informed, so that I'll know if I should follow it or if I should advise him to stop, especially since my mom now does the same thing too after I told her my dad gets better mileage.

Depends on the car if shifting to N or D will give better FC.

Some cars shut down their fuel injectors during "coasting" when in "D". The fuel injectors will be running on normal idle cycle if you are "coasting" in "N".