4X4 vs 4X2 fuel mileage

[RetiredWrench]

I own two Explorers. A 2002 two wheel drive and a 2004 automatic four wheel drive. They both have the 4.0 v6 with the 5 speed auto trans. The two wheel drive one was getting much better fuel economy than the four wheel drive one. They are both primarily driven around town. I purchased the four wheel drive version for it's advantage in the snow during the winter. I decided to remove the front driveshaft on the 2004 and see if that would improve the fuel mileage. It did, and now both vehicles get about the same mileage. I picked up about 5 mpg around town. I plan on putting the driveshaft back in before it snows.

 

[trucku]

Great info

You getting any warning lights since you pulled just the shaft?

 

[RetiredWrench]

No.

 

[aspitaletto]

thats crazy!!! how difficult is it? any special tools ?

 

[RetiredWrench]

No special tools required. Just unbolt the shaft. I screwed some bolts into the empty holes on the transfer case flange, just to keep the dirt and rust out. Remember that you won't have the traction advantages of 4wd.

 

[CDW6212R]

Interesting, and I wonder if the electromagnetic clutch is being powered full time? The front shaft has to turn at the same speed as the rear, or the clutch is engaged. I mention that in case it will add wear to the clutch. I don't know if it's like an AC clutch, but I'd bet that it does wear out with use. You might want to try separating the brown wire to see if that changes anything. If an error light comes on then that would indicate that the clutch is being powered full time. Also if the front shaft could be viewed turning now, but not with the brown wire disabled, the clutch has been powered full time. Good luck,

 

[aspitaletto]

...Remember that you won't have the traction advantages of 4wd.

Ill keep that inmind the next time im at the drive through at McD's !

 

[Curtis]

Interesting, and I wonder if the electromagnetic clutch is being powered full time? The front shaft has to turn at the same speed as the rear, or the clutch is engaged. I mention that in case it will add wear to the clutch. I don't know if it's like an AC clutch, but I'd bet that it does wear out with use. You might want to try separating the brown wire to see if that changes anything. If an error light comes on then that would indicate that the clutch is being powered full time. Also if the front shaft could be viewed turning now, but not with the brown wire disabled, the clutch has been powered full time. Good luck,

I too would like to know if the transfer case output for the front is turning with the front shaft removed. If it doesn't move, that would be ideal.

As for the BWM... some say it does more harm than good. I haven't been convinced of that yet. If the t-case never gets the signal to engage and you spin the rear wheels, what harm can occur? Wouldn't it be the same as revving the motor in a manual car when in neutral? Maybe I'm thinking about this as being too simple?

 

[CDW6212R]

I have had those thoughts also, as I am installing a BW4406 with the same kind of E. clutch.

I think that wear of that clutch comes from friction like any clutch. If the two parts are traveling the same speed, like normal operation on road, no wear should occur. If the front isn't turning, then the question is do the two parts not touch at all with the speed difference.

I'm going to try to operate my TC with an Expedition GEM, which will have 2WD as a selectable position, plus a mechanically locked 4HI position. In 4HI the Explorer 4WD system uses the E. clutch to hold the front shaft.

 

[Curtis]

I have had those thoughts also, as I am installing a BW4406 with the same kind of E. clutch.

I think that wear of that clutch comes from friction like any clutch. If the two parts are traveling the same speed, like normal operation on road, no wear should occur. If the front isn't turning, then the question is do the two parts not touch at all with the speed difference.

I'm going to try to operate my TC with an Expedition GEM, which will have 2WD as a selectable position, plus a mechanically locked 4HI position. In 4HI the Explorer 4WD system uses the E. clutch to hold the front shaft.

That would be the deciding factor.
If the 2 parts of the clutch are touching, then yes I can see wear occuring during a burn out with the BWM.

 

[Thelt]

I am surprised it made that much difference. The front should only be getting power when the rear wheels slip.

 

[Curtis]

I am surprised it made that much difference. The front should only be getting power when the rear wheels slip.

you know maybe that's an indication that the 2 parts of the clutch are touching all the time and causing resistance on the transfer case. But by removing the drive shaft the t-case no longer has the resistance of the front wheels and therefore affects mpg.

 

[Thelt]

you know maybe that's an indication that the 2 parts of the clutch are touching all the time and causing resistance on the transfer case. But by removing the drive shaft the t-case no longer has the resistance of the front wheels and therefore affects mpg.

Could be, I would have to think about disconnecting mine if it meant 5mpg.

 

[dtholmanmax]

Is this something I could do with my very elementary mechanical knowledge? I'd love to pick up the MPG also. How about a how to - even if it's VERY simple - humor me...

 

[Thelt]

What mileage were you getting prior to pulling the shaft?

 

[RetiredWrench]

The transfer case flange does rotate when I drive forward. I don't know if it is from the clutch being engaged or not. I was getting 10-12 around town before. I now get 15-17. There is a big difference on coast down, less drag. The u-joint on the front driveshaft is pretty tight and may be sticking. I plan on replacing it before I reinstall the drivesahft in the winter.

 

[Hitchhikingmike]

Here is something to consider...

Where are the speed sensors on the wheels that the auto 4x4 system uses to detect slippage to engage the clutch momentarily? Are they located in the transfer case or does the system use the same sensors as the ABS system uses?

The location of these gauges are crucial if the front drive shaft is taken out. If the sensors for the front wheels are located on the hubs themselves, then the 4x4 system would not detect slippage if all wheels are moving at the same speed while the front drive shaft out.

If the sensors are located inside of the transfer case to detect slippage, then with the front drive shaft out, the front drive shaft would not be turning the transfer case and then the 4x4 computer would always be detecting slippage ever second you are driving.

If the later is the case then the clutch would permanently be engaged everywhere you drive with the front drive shaft out.

Just food for thought.

 

[02XLS]

The transfer case flange does rotate when I drive forward. I don't know if it is from the clutch being engaged or not. I was getting 10-12 around town before. I now get 15-17. There is a big difference on coast down, less drag. The u-joint on the front driveshaft is pretty tight and may be sticking. I plan on replacing it before I reinstall the drivesahft in the winter.

I get 15 -17mpg around town w/ my '02 XLS 4X4 - 4.0l. I think you have other issues. 10-12 around town even for a big V6 is way too low.

 

[daprez1963]

I have had both 2wd and currently 4wd exp's....I got 15-17 in city on the 2wd and 14-16 on the 4wd one. i think you had other problems to begin with because 10-12 is definitely out of an average range for both. tire pressure, tune-ups, gas selection, a/c or not, weight loads, and driving styles have more to do with your mpgs then to simply disconnect items that were not meant to be disconnected. i would seriously rethink modifications such as that as it might lead to something unsafe in the future. while gas prices will make people try to find ways to improve mpgs, you might consider coasting to the next red light and save both gas and brakes instead of stepping on the gas and flying thru the intersection, missing other cars with the right a way...lol

 

[dtholmanmax]

I get 15 -17mpg around town w/ my '02 XLS 4X4 - 4.0l. I think you have other issues. 10-12 around town even for a big V6 is way too low.

I too get 15-17 around town - 2005 v6 4x4 XLT. Even with the 265/75/16s. I was getting more like 17-18 with the stock tires. I baby it though, to get the most out of it.