We just drove to Arizona and back... two tanks of gas... one low grade and one Tier one. These were ALL highway miles... and typically we hit 36 MPG to the penny on ALL highway miles.

This trip:

24 MPR low grade gas
26 MPG tier one

Any theories? And YES... I'm sending the car to the shop.

 

(overall) Maybe you were going up hill on the way there, and downhill on the way back? Also, climate going there may have been worse? Better on way back? Wind against you, and with you on the way back.

 

Whats the temperature where you normally drive your car, and what was the temperature on the way to and during your stay in Arizona?

 

Low tire pressure(s)? Check them, they should be around 35psi, 32psi minimum. I run my TCH tires at 40psi. Driving from San Diego to Phoenix Arizona and back I got 40mpg with the AC going - it was about 100F that weekend.

Unlikely but possible is a dirty air filter. I assume your speed was about the same as when you got 36mpg.

The OBDII system will cause the check engine light to come on if there is anything odd going on. In the absence of a check engine light, I doubt the dealer will find anything. Most likely they will "clean the injectors" and say nothing is wrong...

Good luck. Let us know what you find out.

 

Consumer Reports says tire pressure and a dirty air filter have little effect on gas mileage:

http://autos.msn.com/advice/CRArt.as...tentid=4024120


IMPORTANT DRIVING TIPS THAT HAVE LITTLE EFFECT ON FUEL ECONOMY

Keep tires inflated. Our tests show that driving on moderately underinflated tires is more of a safety concern than a fuel-economy issue. We set the pressure in all four tires to 10 psi below that recommended by the automaker. This reduced highway fuel economy slightly, by about 1 mpg for the Camry and by a much smaller margin for the Mountaineer. But more importantly, underinflated tires provide much less grip for turning and stopping and run much hotter. Overheated tires wear faster and can lead to a blowout. Check the pressure of your vehicle's tires at least once a month, when the tires are cold. Also check the tires before and after long road trips. The recommended tire pressure is found on a label inside the car—usually in a doorjamb, inside the glove-box lid, or inside the fuel-filler lid.

Keep your air filter clean. According to our tests, driving with a dirty air filter in modern engines doesn't have a significant impact on fuel economy, as it did with older engines. While fuel economy didn't change, however, power output did. Both cars accelerated much more slowly with a dirty air cleaner. We drove both vehicles with their air cleaners restricted and found little difference in gas mileage with either engine. That's because modern engines use computers to precisely control the air/fuel ratio, depending on the amount of air coming in through the filter. Reducing airflow, therefore, caused the engines to automatically reduce the amount of fuel being use

I agree that if the "check engine" light isn't on that it's probably not the engine/fuel injection causing the problem. Could it be something like the emergency brake not fully releasing or an alignment problem?

 

I think Nash was saying that he inflates his tires higher to get better gas mileage. The above report refers to under inflating.

 

I thought he was offering an explanation of why Marianne lost 10-12 mpg on her recent trip.

Plus if running your tires under inflated doesn't reduce gas mileage that much, according to Consumer Reports, then I don't see how over inflating them would increase it that much either.

 

I just got my altima so its a new motor but I drove from Dallas to OKC which is 200 miles and computer stated I was getting between 27 - 28 mpg, I was avg. 76 mph using the cruise and it was up hill. 30 miles of the 200 were at lower speeds and I got around 30 mpg.

wish the computer would tell me when the car is out of gas instead of going blank when I have about 1.5 gallons left guess its a safty issue oh well.

Still 30 mpg is better than my wife's honda accord 2.4L that gets 21-23 city

 

This indicates a mechanical failure. We've done many long drives... and cruising at 80 miles per hour we still get 35-36 mpg... and we've done this same drive in the same tire/weather conditions and still gotten 36 mpg.

I have a hunch that there is some type of "hybrid" feature failure that when the doohicky dies... it leaves you with an ordinary Altima that runs perfectly fine.

Gripper IGH LLoyd... you guys really know car mechnics inside out. Is there any feature of the car that could drop out of function and leave someone with a normal (non hybrid) car or anything like that? There is a real diversity of MPG that different people are getting... while their cars seem to run just fine and under similar conditions. I just had my MPG drop through the floor... and nothing is different about my driving or my driving conditions.

 

I don't think it could be something subtle, like tire pressure. Too much difference for that - you'd practically have to have a flat tire for the difference to be this big.

The main things I can think of are extra sources of friction (e.g. parking brake not fully disengaged), a defect in the engine timing, or a defect in the batteries or their charging circuit. The problem with all of those ideas is that I would expect a "check engine" light or some other obvious warning.