I drive 95% highway, very mountainous, heavy winds. We put almost 50k miles on our 05 AWD. About the best I could do with the 05 on our usual route was 27 MPG.

We just traded the 05 for an 08, to get the new creature comforts and also hoping for better mileage. We decided we didn't need the AWD.

I estimated that I would get 3 MPG better -- 2 because of FWD and 1 because of better aerodynamics on the 08. I'm happy to say that I'm getting 32 MPG, 5 better than before, and that's after only 600 miles.

Of course, I don't know how much of the 5 MPG improvement is because of the switch from AWD to FWD and how much is because of the improvements in the 08 compared to the 05.

We also love the 08 style and interior improvements. With gas prices high and the $3,000 tax credit, I really don't understand why Ford isn't selling more of these. They're extremely well made cars and I'm proud to drive one.

Mark

 

I swapped from an 05 4WD FEH with 33,000 miles on it to an 06 4WD FEH with less than 4,000 miles not too long ago. I now have 9,000 miles on the 06 & for some reason I am getting dramatically better mpg with the 06 than I ever did with the 05.

When I checked my ScanGuage II yesterday, I was at 34 mpg for the current tank. I don't think I ever once got that high with the 05 except for short distances.

~John

 

That's amazing that there is such a big increase in mpg from AWD to FWD. Is that pretty much attributed to weight? I wouldn't think it would be driveline losses because the AWD is essentially a FWD vehicle until there is slippage, correct?

What's interesting is that when you look at the main page for GH's mpg database, there is a big difference between FWD & AWD FEH, but not much of a difference between FWD & AWD Highlanders. I wonder why?

 

That second statement is very much more interesting than the first....
Hmm....

 

If I've read the information correctly from other posts I guess its because the FEH is a REAL AWD system. It uses differentials to send power to the four wheels appropriately, it sounds like the Highlander ONLY sends power to the back wheels electrically (I can't confirm that but thats what people have said on the group--I'm not even sure how one does that with a transmission easily).

In that case I would think there is some power take off and drag from the back wheels on an FEH at all times... Its front weighted (ie MOST of the power goes to the front until you slip) but its not like theres some sort of switch. Mind you...this is what I've inferred from other posts... I've love for someone with actual knowledge from the books to confirm this for both machines.

 

The AWD Escape hybrid loses some efficiency in FWD mode due to the inertia and friction losses from the power take off on the trans and driveshaft which are always turning when the front wheels are turning. The clutch pack that engages the rear wheels to enable AWD in front of the rear diff also probably has some parasitic drag. I think it uses multiple wet clutch discs/plates like those in a conventional automatic trans.

The Highlander does use an electric motor to power the rear wheels on an AWD version of the vehicle. Max power is 50kW.

 

The mileage difference between 4WD/AWD system and the FWD system is really more about the additional loss of energy to friciton in the drive train.

My '05 FEH still has only around 18000 miles on it. I checked the engine oil and air filter and found both were a lot dirtier than I expected (it's been getting oil changes more frequently than required). Just changing an air filter can make a huge noticeable difference in fuel economy (I've heard "claims" that it can be as much as 20% -- I find this hard to believe though I think that 10% is easily believable) and this in itself can account for a 3 mpg fuel economy difference.

The point is you have to be careful when comparing a car that's been service for a while to one that's brand new. I expect that even if Ford didn't change a thing between model years and theoretical economy would be expected to be unchanged, you'd still notice a difference just because of things like comparing the mileage of a car with a dirty air filter to a car with a clean one.

 

This diagram might help illustrate the losses in a ICE vs. a electric drivetrain (and explain the differences between the Highlander and Escape 4WD systems.) A hybrid has roughly 50% energy loss.

I still have at least a month for my 2008 FEH to arrive (the most efficient SUV on the market for now), my next vehicle will be a plug-in electric vehicle.

 

I think that is a little deceiving, a lot depends on drving habits, what climate they are driven in etc etc etc

I have driven a FWD FEH & have owned two 4WD FEH's, I find the 4WD cuts aroung 2 mpg in general.

~John