Also noticed that...
My 4wd XLS in 2wd gets it's best mpg at
55 mph/about 1600-1700 rpm/26-28 mpg.

Declines from there...
60 mph/about 1700-1850 rpm/23-25 mpg.
(No mods yet, just 5-20 synthetic oil.)

 

shouldnt make any difference whatsoever, as its taking the exact same amount of force to turn all the componants.

 

I have returned from my small trip and will post my observations as soon as I get into work, to sum it all up, there is a bit of fuel economy to be expected from 2WD setting, but not considerably enough in my opinion.

 

That doesn't make sense to me, surely they can't justdesign a feature which disengages itself and claim it it improves fuel economy without evidence, they must at least havetest resultswhich back up their claims, and surely the engineers behind it wouldn't have designed it with the knowledge already of everything still moving would make no difference!

 

I think many brews thinks that just because the prop shaft and the rear axles are still spinning when the clutch is disengaged(2WD) that since everything is spining the engine is working just as hard as if the clutch was engaged(4WD), and that my friend is wrong. When you engage into 4WD yourtransfering some power tothe rear wheels while still maintaining power on the front, and esentially making the engine work harder. just because when seton 2WDall the 4WD components are spining doesnt mean they are putting a load on the engine, the only load put on the engine is that of the weight of the prop shaft, the rear axle spins freely as the car moves forward as in any car. From what I noticed in my trip the MPG droped notisable in the stop and go of the city, probably about 1mpg wich matches whats advertised. But when I hit the highway, there was a varry minute drop of probably less than half mile per gallon, barely notisable. So I decided I willdrive in 2WD on the city unlessweather conditions force me to use4WD, Although driving on2WD inst that much economical than 4,I will drive in it for the most part, that 1/2-1 mile per gallon willaccount for some fuel savings in the long run.

 

let me explain how this system works..
transferring SOME of the power to the rears has absolutly no effect on the system. Wether or not 100 percent goes through the front, or 50/50 goes to front/rear, it makes no difference on the drag on the driveline as ALL the componants are spinning regardless of 4WD setting. There is no "extra" drag on the system when you engage the electromagnetic clutch on the rear differential. The axles, rear diff, and propshaft all suffer the exact same amount of drag whether or not they transfer power.
The load on the engine is exactly the same, assuming you're not spinning the tires.
the one and ONLY place this could make a difference it if you made many, many small u-turns or sharp turns, as some energy will be wasted in rear clutch slip.
thats it.
keep in mind that the propshaft is spinning due to the fact that the transfer case and transmission are always spinning it, not the road. So that load hasnt changed at all.
the car also needs to expend the same amount of energy to spin the rear differential and axles in 2WD, as you need the engine to overcome the added drag of those componants.

you all can test till you're blue in the face, but if you keep testing over and over you'll find that the milage will be within 1-2 percent regardless of 4WD setting (which is well within a normal operational window, as milage will easily change that much due to a thousand different conditions).

truth is, the ONLY reason the "2WD" option is on there is because consumers requested it. The 4WD system on this truck is identical to dozens of other cars/trucks on the road, and nearly no one offers a "2WD" option, because its just plain silly.

 

Iunderstand nowwhat you mean behind the theory of operation of the system, but how do you explain the increase in MPG that I observed while on 2wd, note that I did both calculations while going up wind and on a verry steady road, minimal bumps and it was at night with verry consistent temperatures, so the only variable was the car it self. Note also that the gain was verry small, probably less than 1 MPG, but gains none the less and would add up over time. If your theory is correct we should all write a law suite over tomitsu for false advertising " set the dial to 2wd for economical driving".lol.

 

1 MPG is well within an allowed difference.. You could have easily been cooler outside one day, or less humid, etc.etc.

I dont believe Ive personally seen any advertisment stating that you will get better milage in 2WD, but I admit to the fact that I havent done a lot of research on all the marketing.
The only possible difference between 2 and 4WD is that in 4WD you will have a heavier electical load (to activate the rear clutch), thereby causing a slight amount of added drag on the engine via the charging system.. But thats really grasping.

 

I can't say I've read it in any satement by Mitsu either, it's mostly showing up in reviews but
my dealer stated 2WD for greater fuel economy when explaining the controls at hand-over of the vehicle, he must have been briefed by somebodyat Mitsubishi!

 

However or wherever it's engaged, there's going to be some driveline friction between the point of disengagement to the hub