I searched the FEH forum, and didn't find any discussion on this yet.

When I entered my most recent tank in the database, I spent a little time perusing through the FEH numbers. The FWD gets better gas mileage than the AWD equivalent.

Now I'm an academic person, so I looked for certain trends that may throw off the data, and didn't find any. The mileage in both is similar, as is the drive times and number of tanks per car, as well as number of vehicles. The temperatures recorded are actually lower in the AWD database. Yet the AWD seems to get on average 3 gallons/mi less than the FWD. This may not seem like a lot, but makes a difference in breaking the 30mpg barrier in an SUV.

So, is the AWD less FE than the FWD? If so, this is a good thing for new buyers to know since the four wheel option of the AWD is rarely used in most situations, and costs more when you buy the car. I bought an AWD Explorer for my first SUV thinking I'd need it in snow in the Midwest, and ended up never employing this feature.

30+mpg vs. 20+ mpg with a minimal decrease in cargo-room -- why should someone consider a nonhybrid?

The AWD simply has more weight and more friction from the AWD components, which in turn decreases the FE. Sometimes I wish I had purchased the FWD model to get the better FE, but when we get a pile of snow in the winter and I have to climb our steep driveway, I know it will handle it. The peace of mind is worth it to me.

My 4WD
Wife's 4WD

EPA fuel economy numbers, though highly inaccurate, always show a difference between 2wd and 4wd drive vehicles across the board. As mentioned, due to the added components a 4wd vehicle will always get fewer miles per gallon than its 2wd equivalent.

-Tim

2006 Mercury Mariner Hybrid AWD
Black with Pebble interior
Premium Package with Nav & Moonroof



Current ODO: 26,152
Typical Drive: 20 min crosstown in heavy traffic (3.5mi there and back twice a day)


532 Gallons of gas saved
That's 10,642 lbs less CO2 emitted

Then might it have been better for Ford to have went with a 4WD system instead of a full time AWD system on the Hybrids? This way, one could simply disconnect (via a clutch) the all the "extra stuff" in the summer, and therefore not have all those extra components active?

Even then, you still have to lug around the weight. The numbers will still be different, maybe slightly closer but its only 3 MPG different now.

AWD costs more, has more components so is more likely to need repairs and gets lower FE. If you need it go for it, but if you don't encounter a lot of snow or do off-roading then I'd go for the FWD.

I live in southeast VA where we don't get much snow and never go off-road, so I used that same logic when I purchased my 1997 Explorer.

It is not really a "full time AWD system". Ford's "intelligent 4WD" runs as a FWD until conditions demand the AWD, then the rear wheels kick in automatically as I understand it.

~John

I don't even think a system that "disconnects" the rear wheel system would result in much of a reduction. While the added weight is part of the issue, I think the friction is a bigger one. Even if the rear axles, shafts, transfercase, etc. are not being powered, they are still turning as the vehicle moves. There is friction and thus work required to turn these parts. That work is not done directly by the engine in this case, rather it is transferred to the rear wheels and thus creates work for the front wheel drive system to pull them along. I don't think that in a 4wd system that the rear wheels spin freely of the rear axles, etc.

-Tim

2006 Mercury Mariner Hybrid AWD
Black with Pebble interior
Premium Package with Nav & Moonroof



Current ODO: 26,152
Typical Drive: 20 min crosstown in heavy traffic (3.5mi there and back twice a day)


532 Gallons of gas saved
That's 10,642 lbs less CO2 emitted

They should not be still spinning if the hubs are unlocked.

In other vehicles with selectable 2WD/4WD, their font hubs unlock (manually or automatically) to prevent the front drive components from turning when not in use. These are vehicles where the rear wheels drive when in 2WD mode. In the FEH/MMH, it is kind-of the other way around, but the principles should be the same. Instead of using locking hubs on the front wheels, the FEH/MMH would use them on the rear.

However, yea, there is still the extra weight of the components.

Also remember that the 4WD FEH sits a couple of inches higher... this likely changes the wind resistance--higher or lower I can't say... with the weight and everything however I can't say I'm terribly suprised by a 3MPG difference.. If anything I'm suprised its not more.