I've had a couple times when I accidentally put in high octane and seemed to get better MPG... but I've been told repeatedly by the experts that this is my imagination.

 

Iboom, I would have the dealer check out your car. As another post said, "you should not be trying that hard". I have raced (hard acceleration, competing with other vehicles, high speed bursts to 95-100) over 1 or 2 days but was always able to get the mpg for that tank back up close to 40mpg. For the high heat situations, i have noticed that any temp over 95F causes the ICE to run more often, similar to cold temp driving. My tests have not shown any significant difference between using AC or not (probably 1 mpg) I believe the AC keeps the EV battery at a more efficient operating temp via the air transfer duct on the rear deck. You can check out some of my photo data at www.thespoils.8m.com , you will find winter data compared to summer data and top tank range. I am hesitant to say this, but driving technique is probably a huge factor. When I first purchased the NAH the mpg display showed 24 mpg (from others who had test drove my car for the first 199 miles) that was a concern because I would not keep the car if that was going to be the mpg. After I filled the tank and drove the car as a hybrid, I immediately realized that the hybrid must be driven as a hybrid and not a regular car. I do think you are driving properly therefore, get the car checked out. Bring the log from this database (if it is not too embarassing)

 

I too have been averaging ~28 mpg during normal driving (mostly urban). I've had the car since December 07 and it has about 4,500 miles. If I try extra hard (conservative acceleration, using cruise control whenever possible, and driving under 40mph) I might manage to get 35-40 mpg for about a quarter of a tank at which point I give up and continue driving normal again. The one thing I've been noticing more often, is the needle on the power meter not dipping all the way down during braking on occasion. The hybrid batteries stay relatively charged so I'm not too concerned, but it seems odd that the regenerative system appears to not be working optimally.

 

There is a 'regen brake' linear potentiometer that sits at the base of the brake pedal. It is very loosely attached and is not unlikely for it to wiggle around and slightly change position, thus changing when your car does regen.

I had brought in my NAH to have the dealer lubricate my brake pedal (it was squeaking). When they gave it back to me, they told me that the regen brake switch was the one causing the squeak so they replaced it. But because of the replacement installation, it was fairly far from the brake pedal causing it to register far too late that the car was braking and it was mostly using the regular brakes, not regen.
You can ask your dealership to adjust the switch (or if you want to avoid them screwing it up more badly, just adjust it your self to be a little closer to the brake pedal). Your regen will engage sooner and harder with just a light tap on the brake pedal preventing you from wasting energy as heat in the real rakes :-))

 

This is normal under 2 conditions. 1. The battery is fully charged and will not accept the charge (actually the computer will not allow it). 2. The battery is too warm, and again, the computer will not allow the charge.

The computer is very protective of the battery in order to prolong it's life.

 

Don't forget the NAH has a heat sensor that cuts regeneration to the battery if it gets too hot. It is not designed for interior heat beyond 100 degrees which can easily happen if the exterior temperature is in the low to mid 90's and the car is left in the sun. The vent on the back shelf is the only thing that keeps the battery cool so you need AC on at really hot temperatures. I have actually hit these numbers a few times and it is weird hitting the breaks and watching the needle not go in to the blue. This is one of the big reasons our Arizona and Florida friends don't always get good mileage in the NAH. AC can be your friend.

 

The hot temp makes the most sense for why it isn't fully regenerating during braking. It has been in the upper 90's-100's for quite some time now. It does make sense that it is a safety mechanism that is preventing the hybrid batteries from overheating.

Thanks for the help in clearing that up...

 

I too have noticed the unusual regen braking (not being as aggressive). I also attributed it to the high heat. I did turn off the engine and it immediatley started to regen normally. Not sure what the reason but it would appear that the computer has some say in it.

 

As a quick update, I just got back from running a few errands with the a/c full blast in an attempt to keep the batteries cool, and the regenerative braking was working flawlessly. I never would have guessed that I would be getting better mpg with the a/c to the max. This car seems to defy logic.

 

The NAH is like my TCH in that regard. Since I live in the mountains and must descend several long slopes in each direction of my commute, I always use the AC on the down slope after the battery has topped up because the extra kinetic energy from the remaining downhill portion has nowhere else to go, and so will be lost. You can use it to cool the cabin and thus the battery. Since the power is being put right back into the battery -- its free!