Full time 4 wheel drive gas mileage

[Sal Lubrano]

I own a Jeep Grand cherokee and it has full time four wheel drive. A viscious coupling in the transfer case it divers 50% front wheels and 50 rear until there is some form of slip. My question is why would my jeep burn more gas than an identical jeep with a part time 4wd where it is 2 wheel until you manually switch it to 4wd. I always hear this from people but it does not make sense you are still moving the same mass with the same gears?? Is this true? If so how much differnce do you thik there can be?

 

[Quiky One]

My truck gets 15-16 around town 2wd, my moms tahoe gets 12-13 4wd...just an example

Jason

 

[John Larkin]

I believe you are pushing more mass with FT4WD than PT4WD. The transfer case is always engaged in FT4WD. There may also be a lower gear ratio associated with FT4WD which would increase your RPMs, hence lower MPG. That's about enough acronyms for one subject.

 

[86SS86LS]

My 93 Jeep Grand Cherokee has 2WD, Full Time 4WD, and Part Time 4WD. So I've got the best of both worlds - 2WD for economy and Full Time 4WD for snow and ice. I believe just the Limited V8's had Full Time 4WD only.

 

[Quiky One]

My 93 Jeep Grand Cherokee has 2WD, Full Time 4WD, and Part Time 4WD. So I've got the best of both worlds - 2WD for economy and Full Time 4WD for snow and ice. I believe just the Limited V8's had Full Time 4WD only.

Nope...Sister has a V6 Limited and it is alltime AWD.

Jason

 

[SouthernCal GN]

I own a Jeep Grand cherokee and it has full time four wheel drive. A viscious coupling in the transfer case it divers 50% front wheels and 50 rear until there is some form of slip. My question is why would my jeep burn more gas than an identical jeep with a part time 4wd where it is 2 wheel until you manually switch it to 4wd. I always hear this from people but it does not make sense you are still moving the same mass with the same gears?? Is this true? If so how much differnce do you thik there can be?

Simple- more friction to overcome. You're driving both the front and rear drivelines at all times, plus the center diff.

Part time systems have a transfer case to split the output power to front and rear, but no center diff- that's why you don't want to drive around on dry pavement in High 4 or Low 4- ther's no center diff to compensate ffor slippage between the front and rear pumpkins. On the older Quadra-Trac systems, we used to pull out the center diff, and replace it with a standard chain drive set up; we also installed manual hub locks.