If the engine is spinning, neutral should be fine at any speed.
If the engine is not spinning, don't do 70 miles per hour in neutral.
Sorry for the winded explanation.
-ed

 

I'll keep it in gear and pay for the extra gas I use, thanks!

 

+1

 

I have done something similar several times, but with the gear in "D" mode. I started off in e-mode at 40mph at the top of the hill, and as the speed increased, the engine rev'd up but the instant mpg needle stayed pegged BELOW the 60mpg mark (if you have the us version of the TCH you should know what I'm talking about). I have reached speeds as high as 57mph on that downhill.

Anyone in NJ who wants to try this out should drive close to the GW bridge, there is a road that goes downhill leading directly to RT 46. RT 5 and RT1 or 9 South could be reached by exiting at the bottom of the hill. If anyone has questions of which road it is in particular, I'll get the info for anyone who requests it.

 

Every time I try to coast in "D" over 42, the needle moves out of blue to the 60 mpg mark.

 

That's simply because the engine is running, but does not mean you are consuming fuel.

It's too bad the way that gauge reads, at least in the U.S. cars. On the Canadian cars, it moves out of the blue to 0 (0 litres/100kilometers), which is much clearer to figure out. Basically the metric gauge measures consumption.

Ideally, with a miles per gallon gauge, it should move from Emode to 9999999999999999999999miles per gallon, or to be more correct, "infinity" miles per gallon, but that's an impossible gauge.

While not always accurate, you can think of it sitting at 60 miles per gallon as using no fuel. (...but to be 100% correct, there are conditions where the car is using fuel, but is getting better than 60mpg, and you won't be able to see the difference between that and a true fuel cut.)

Later!

Dang

 

I just think common-sense has to be used in any move toward improving fuel economy. Hypermiling is a good thing, no doubt. The problem starts when you start conjuring up all kinds of methods to increase your MPG that compromise safety. Being able to keep up with the flow of traffic and "reasonably" accelerating and stopping is the most important thing, i think. Driving in neutral with the vehicle in motion is probably not a smart move. You don't need a degree in Engineering to understand that. That still leaves it open to personal opinions and understanding.

 

In many states coasting in netural is illegal.
Don't shoot the messenger.

 

Just a random tidbit for those who may be able to make more from it:
"The HSD "neutral gear" is achieved by turning the engine off. Under this condition, the planetary gear is stationary (if the vehicle wheels are not turning); if the vehicle wheels are turning, the ring gear will rotate, causing the sun gear to rotate as well (the engine inertia will keep the carrier gear stationary unless the speed is large), while MG1 freewheels so no power is dissipated."

http://en.wikipedia.org/wiki/Hybrid_Synergy_Drive

 

One could argue that the TCH is NEVER in neutral. The gears are always engaged and always turning!