Hyper Mileing

[Da Klugs]

Originally Posted by Langod

Be aware that coasting in neutral with most modern automatic transmission cars will actually hurt your mileage. (I don't know if this is true with maunal transmissions too) A modern automatic -- when you are coasting with your foot off the gas, will drop into a mode where it only fires cylinders frequently enough to keep the engine spinning, but while in neutral, it actually uses more gas because it's at a full idle. You can see it on some car's computers -- my wife's Subaru Legacy shows the mpg meter max out at 99.9 mpg (which means it's probably higher) while coasting in gear as opposed to about 65mpg on the same hill/speed while in neutral.

Noticed my Maxima seems to get better mileage in gear also. (tough to tell for real -- no computer display).

I just do it to save more gas money for my '03 SVT Cobra -- has a supercharged V8 that I've gotten down to 2mpg whilst "driving spiritedly". (it normally gets about 18-20mpg around town, though)

Have read the same things re neutral. Not the case on my Audi. Runs at 1100-1200 RPM while in gear and I think the AWD comes into play re the efficiency. In neutral, drops to 800 rpm. Huge difference in the Mpg and the "feel". Closest thing I can think of is my old 70's Saab with the "freewheel" option. Seems much less transmission drag is the difference coupled with the lower rpm.

Got 10.5 on the way to work. I was late and hittin it!

[Langod]

Originally Posted by Da Klugs

Have read the same things re neutral. Not the case on my Audi. Runs at 1100-1200 RPM while in gear and I think the AWD comes into play re the efficiency. In neutral, drops to 800 rpm. Huge difference in the Mpg and the "feel".

Originally Posted by Sancho

This is somewhat more of an instance than the rule, many transmissions dont freewheel while in gear and the slipping is taken up hydraulically etc.

From what I've read, the tranny doesn't freewheels (if I understand what you mean) -- The wife's subaru's RPM is still "normal" for the speed it's going in gear, but like I said it pegs the MPG readout. Moving to actual neutral does drop the RPM to 800 or so, but the MPG readout reads much less.
(According to this short article your car actually uses no fuel whatsoever while coasting in gear.)
I don't know for sure, just reporting what I've read. I'm not a mechanic -- I can understand a manual tranny, but automatic transmissions might as well be magic to me.

And just for giggles, here's an article from Road & Track regarding gas saving tips and myths.