These are contradictory, Higher RPM doesnt mean more fuel and i dont know where you get your information. What I'm trying to get at is that down shifting is better than coasting and turning off you jeep to save fuel. By the sounds of it, you get pretty crappy mileage doing your method so im hard pressed to believe you. I just dont like people spewing false information, especially about hypermilling cause i live in the land of the hippies and i have to deal with dummys all the time. It makes me want to buy a huge diesel and drive around town revving and blowing black smoke.

The next time someone says they are being green by driving a prius, laugh in their face. Ask them where does the heavy metals come from, where are the batteries made, and where do the batteries end up? answer: canada, japan, landfill

 

205k mile 4.0 and AW4 Auto, 3.55 gears, 31" X-Terrain's, 6" of lift, roof rack removed, fenders cut, angle iron bumpers. About 15 mpg average

 

speak it bro lol

 

lots of good poiont on this, anyone take into account there lo-cal diffrent climates and elavations will deff have an effect. but that said still want better mpgs myself. and i think they should b in there i just got find em

 

I got a stock 99 limited with grille guard and it get 15 city 20 hwy

 

Not to mention, how long do rechargeable batteries last? Not as long as a gas engine. And how much would they be to replace? I think american's should be angry, because the heavy metals and acids your talking about come from other countries, but the junk ends up in your country from left over batteries, if people don't recycle them (how many people do you know that recycle batteries?). Imagine fields of batteries, nothing will ever grow there again. I hate hybrid cars. period. sorry to rant...

Anyway I came on here cuz I found an article that I thought was cool, on the side it gives you some percentages that things lower your gas mileage. http://www.exstrom.com/mpg.html
And I saw another one that says roof racks decrease fuel economy by around 5%. I think we probably ALL have roof racks lol

 

this is a good link and a good explanation for people who are not sure why they are loosing mpg's all of a sudden

 

I like also that they have percentages, put it all in perspective

 

I got about 16 MPG the other day but I had her pinned at 75 MPH for a good 2 hours straight.

This is in a '98 2-door auto; all stock except heavy-duty bumper, 235/75/15 M/T's, and hi-flow cat w/ Dynomax cat-back.

 

My "information" comes from scientific research. Consider three things: Ideal gas law, Simple math, and Stochiometric A/F ratio.

Ideal gas law: P*V = n*R*T pressure times volume = number of moles times ideal gas constant times temperature. Knowing the manifold pressure, and air temperature, you can calculate the amount of air in a given engine cylinder per intake stroke. Higher vacuum = lower pressure = less air.

Simple math: By holding all other variables constant (air temp and manifold pressure) doubling the RPM will double the number of intake cycles per minute and the amount of air entering the engine per minute.

Stochiometric mass A/F ratio: Typically this is 14.7:1 (14.7 lbs of air per each pound of fuel). Stoichiometric air/fuel ratios are not necessarily the optimal target for best power or economy though. For best power, you will want to run rich, for best economy you will want to run lean of stoich. If you increase the amount of air going into the engine you will have to increase the fuel as well to prevent a lean combustion event and overheating the engine. If you think that increasing your RPMs by downshifting uses less fuel than coasting you are mistaken.

One final note: If you decide to buy that diesel to blow smoke, get an older one. We are constantly working on technology to reduce diesel smoke on newer engines to the point where they pollute less than gas engines. Better yet, get a new one, support the economy, and help support my company!! I need to buy some new test equipment next year.

 

Try 48 and being a "junior member". I feel so dirty.

I have a 2000 4.0L Sport w/176K, 27" tires, 3" lift - 19.5 MPG on the highway driving 65 MPH.

 

Car makers are not stupid and thought off this 20 yrs ago. During engine braking, fuel is not needed cause that would void the reason for engine braking. Stoichiometric ratios are important for emissions and making power but doesnt matter much when you dont need power and just pushing a bunch of air.

http://en.allexperts.com/q/Automotiv...ne-Braking.htm
http://www.ecodrive.org/The-golden-r...ing.249.0.html
http://www.popularmechanics.com/cars/how-to/4230705
http://www.autoshop101.com/forms/h43.pdf

search DFCO or decelerating fuel cut off. Car companies care about mileage so they try to squeeze as much of it out of their motor while still being able to make ample power

 

The thing I dont like bout this is they say that the engine uses no fuel when your off the throttle coasting down hill, which i agree with. But they then say that you use more gas goin into neutral and coasting. Again I agree. HOWEVER!! if you let off the gas goin down a hill your gonna loose more momentum due to the engine now acting as air pump opposed to coating in neutral.

 

It really depends on the size of hill/mountain and the gear you use but the point of down shifting is to use the engine to manage your speed. I can just leave it in 5th gear while i'm going down a 7% grade into SC and not really change my speed at all. If i coasted i would be on my brakes the whole time, 4th i increase speed and 3rd i slow down

 

With all the stuff on this Forum It's hard to believe that none of these 4x4 add on manufactures have not come out with a way to unlock the front hubs from the axles just like the old manual locking/unlocking hubs. This should help with MPGs no? Or do they have this for an XJ. Wouldn't it stop everything in the front from turning?