bingo. that's the reason for your decline. try to use open windows (all 4) to cool down at city speeds, and ac on low in the 70s on the fwy.
fill tires to sidewall max, at least; not owners manual max or dealer recommendation. they may not know much about driving for fuel economy since they are new to the hybrid business.

 

I think we may need more detail.

How is the regen working? Do you ever find that when braking, you do not see the gauge going into the blue area?

Do you sit for any prolonged periods of time (in EV) with the A/C running?

Keep in mind that this car has an electric A/C compressor. It directly competes with the battery reserve that the drive motors use. For example, if your car is sitting at idle, with the A/C running, it will draw down the battery fairly quickly. At some point the ICE will have to come on to recharge it. This will effect your mileage pretty drastically. Whereas running the A/C at highway speeds does not effect mileage nearly as much. Although the electric A/C is much more efficient than a belt driven compressor, it does suffer under certain scenarios. Namely sitting in traffic.
I think this design is meant to keep you cool at typical red light stops (of several minutes or less). Beyond that, it needs to run the ICE.

If you find the car is not "going into the blue" during deceleration or braking, you have a different problem, your batteries are getting too warm.
When this happens your car is no longer a hybrid. The computer simply shuts down the battery for the most part, you do not get any benefits from storage (regen) or drive assist from the electric motors.

 

I agree with IAN33 comments concerning psi and the AC, as I experienced and was able to duplicate and test the effects of both. Your tire psi sidewall max should be 44. Try increasing the psi (use an accurate gauge, I have 3 and all three show slightly different psi readings) As far as the AC, I always use the auto feature with re-circulate on and temp at 75F. Being in the "auto mode" the compressor will cycle on and off and will also automatically adjust the fan speed to maintain the selected temp.
Let us know how that works.
PS. you will probably also enjoy the ride and handling with increased psi.

 

I'm not 100% sure the PSI on my tires is the solution and I'll tell you why. First off, I was getting 34 - 35 mpg orignally that was with a little hwy miles. Total hwy mileage I was seeing 36 - 37 mpg. Note this was with 35psi on my tires. I believe this is related some how to the A/C unit and the charging system in my battery. I do not sit and idle for long periods of times but when I try to hypermile w/the a/c on and driving beyond 40mph it seems to drain the battery faster than it used too.

 

This seems like you might have an issue with the battery pack (it holds less charge, possibly due to a dead cell...).

I have my AC set on 60 and have the fan set to the lowest speed (the first tick) and its always on whenever I am in the car. I get 40s in the city and 35s on highway, so I doubt the AC is your problem! I also never mess with tire pressure and just keep it at the recommended.

All in all, given that you used to get good gas mileage and then your city dropped sharply I would suspect that the battery is not retaining as much charge as it used to. Ask your dealer if they have some way of verifying how much charge the battery is holding.

Another thing you can do is find an extremely flat road, get your car to 40mph, have the EV kick in, and then put it in cruise control mode. Observe how long it stays in EV and how quickly the battery drains. I can get mine to go about a mile in EV on half a battery charge, so it stays in EV for at least 1.5 minutes @ 40mph with CC on.

 

Yes I often suspected that there was something wrong with the charging system and that the hybrid system was not working in conjunction with the gas motor. I forgot to mention to everyone that my car sat on Nissan's lot for 6 months before I bought it. The only reason I know this is because I did a carfax.com report on it. I've also had computer problems in the past that the dealership said didn't exist until the car started acting up again. lol I've had nothing but trouble with this car.

 

I really suspect the heat, a/c & to a smaller degree the tire pressure are the cause, I have a hch but, for example, today is the first 75 degree day (non 95 degree) on this tank.... as such, still having the air at 72, my battery charge went from 3 bars to 6 bars, my gas mileage went up by 1 mpg on a 12 mile drive with a stop at the mid way point for lunch, stop & go driving etc....this is amazing seing I have spent most of this tank fighing to keep 2-3 bars and consistantly declining mileage.
I have said it before, hybrids appear to work best at temputres where YOU are most comfortable, 60-75 or so.

 

:-( I partly suspect that since the hybrid system is from Toyota, Nissan mechanics probably don't have a clue how to troubleshoot such problems and thats why they try to avoid you... You need to find some issue that clearly demonstrates there is something wrong with the way your car works and then raise hell to the dealership / corporate. If they keep taking the car in and giving it back to you unfixed thats actually quite ok - just look into the lemon law and you'll see why its ok :-)

I would highly recommned that you perform a test with cruise control on. Just find a flat road, CC at some speed less than 42 and drive as long as the road lets you (preferably no street lights). Record your trip MPG, miles driven, average speed (NAH does all that for you, just remember to reset all the numbers before your test) and also observe carefully when the car enters / exits EV mode, and how fast the baterry is recharging / depleting when in EV. In this scenario the car should average around 35mpg. If you are getting anything less than 30, there has got to be something odd with either the battery, or some other electrical component.

 

I think Ian33 and Steved28 are on to something.

I have the same issue on my car, but confusing me even more is that the temperatures I am seeing this summer are no different than what I saw last summer, which leads me to believe the 12V battery may be bad.

My dealer has had it twice and both time have indicated that nothing is wrong with it. I'm not sure what the lemon law would say if the dealer can't replicate it and keep stating nothing is wrong instead of them verifying a problem and just not being able to fix it.

Otherwise what would keep us from making up a problem to take advantage of lemon laws. Even though you and I both know that there is a real problem.

There is a service bulletin related to the 12V battery, but apparently my VIN isn't part of it. I have an '07 and the TSB covers some '07 and '08 models.

 

The Lemon Law differs by states, but the just of it is that [during the warranty period the vehicle cannot be restored to specifications] after 3 attempts if safety-related or 5 attempts if non-safety-related issue, OR your vehicle has spent more than X amount of days in service.

X for california is 30 days cumulative (that is if you had 6 services each of which took 5+ days, your car is a lemon). For other states X differs, but its either a cumulative total of around 30, or any single service that takes more than 20 days.

For each case it must be a problem that the dealership agress exists and that is where the 'to specifications' wording in the law makes things tricky. As an example, cases for lesser HP-than advertised in sportier cars is very easy to make as the HP rating is a clear specification and is easy to verify with dyno test.
Most automakers shield themselves from making fuel economy a specification however by saying "actual mileage may vary depending on...". What you have to do as the consumer is read your vehicle manual, isolate whatever comes after the ... by 1. using CC to remove the driver factor, 2. compare FE against another NAH that also used CC on the same route on say roughtly the same day. If yours gets <30MPG and the other gets 35 you got a case. If they are 2-3 mpg apart I doubt you will get far in your fight :-(


Note that for the lemon law to start ticking, all you need is any nissan representative to acknowledge (once) that there is/was a problem and take your vehicle in for the service.

It is certainly not going to be an easy process, but as the consumer it is your right to seek repairs for your vehicle when it doesn't perform according to specifications. Unfortunately the burden to demonstrate that it does not perform according to specifications is on you!




As a side-note: my legal knowledge comes from currently fighting a lemon case for my mazda whoose list of problems is longer than this thread :-) I know that it is very frustrating to deal with car problems and the legalities behind it, but often times it is necessary to do so. Don't give in! If your vehicle has a problem, try to isolate it, prove it, and seek the repairs.