Gas milage, wear & tear on system

TJim <jim (AT) ranlet (DOT) nospam.com> wrote:

I've been running my '96 ZJ with Selectrac in "full time" 4WD mode for 5
years now, with no apparent problems. I think the difference in gas
mileage would be negligible and the only additional wear and tear would
be on the transfer case, since the front axles and drive shaft are
turning all the time anyway. The overhead display says I've averaged
17.7 mpg over the last 8000 or so miles (since I last zeroed it out).
I've averages 22mpg on long trips and I've always been in 4WD full time.
My ZJ has the I6 engine.

I'm no expert, though. This has just been my experience with Selectrac.

The 4Hi setting is one of the two part-time settings (4Hi and 4Lo) and
neither of those two setting should be used on the street. Only the one
labeled 4FullTime (4Full?) should be used on the street... and then it can
be used on the street as much as you like, or full-time if you like...
though I see no need to run it unless the weather is bad and the streets are
a little slick.

Jerry
--
Jerry Bransford
KC6TAY, PP-ASEL
The Zen Hotdog, make me one with everything!
See the Geezer Jeep at
http://members.cox.net/jerrypb/

"TJim" <jim (AT) ranlet (DOT) nospam.com> wrote

"Keith Rogers" <keith_rogers (AT) chartermi (DOT) net> wrote


With it in full time 4WD small differences in wheel size will mean the
viscous coupling will be slipping a little all the time. That is what it is
designed for, though. (Keeps the stress from breaking drivetrain parts)

A possible drawback (if you don't really need AWD) would be in a really hot
climate. The viscous coupling heats up due to friction (For the same reason
the torque converter does in the auto tranny).

It would seem that this would be considered in the design. I've never heard
of a x-fer case overheating, just a thought.

It's not like the differences in axle traction are great enough to cause a
lot of slipping. It probably heats up more when it's being used for what
it's designed for (in traction reducing weather) and the wheels are starting
to loose traction during acceleration.

Jerry, Mine's from 1990 (I forget the model right now) and it doesn't have a
4hi part time setting. You can put it into 2wd, 4hi full time, or 4lo part
time. (I wish it *did* have a 4hi part time setting like my TJ does)
I just couldn't see how there would be any more gas usage or wear by having
it in part time 4hi, where the front diff and driveshaft are driven by the
motor vs. 2wd, where the front diff and driveshaft are driven by the wheels
(through the street from the back diff and driveshaft which are driven by
the engine...)
Seems like the engine is doing the same work (maybe even slightly less) in
4wd full time as in 2wd.
TJim
98 TJ SE
90 SJ GW

"Jerry Bransford" <jerrypb (AT) cox (DOT) net> wrote

OK, I looked it up. It's an NP-229. Does anyone know anything about it?
TJim

"Jerry Bransford" <jerrypb (AT) cox (DOT) net> wrote

All right, I can't type what I'm thinking.
I meant to say "full time" not "part time". I have only "full time" 4wd hi
and "part time" 4wd lo ranges.
(Some day I'll learn to proofread my posts!)
TJim

"TJim" <jim (AT) ranlet (DOT) nospam.com> wrote

That's even stranger since I had an '89 Cherokee with Selectrac and it had
2wd, 4Hi, 4FullTime, Neutral, then 4Lo. I've never seen a Selectrac
transfer case with any other configuration.

Jerry

--
--
Jerry Bransford
KC6TAY, PP-ASEL
The Zen Hotdog, make me one with everything!
See the Geezer Jeep at
http://members.cox.net/jerrypb/

"TJim" <jim (AT) ranlet (DOT) nospam.com> wrote

Jerry Bransford <jerrypb (AT) cox (DOT) net> wrote:

The Selec-Trac in my 96ZJ has 2WD, 4 Part-Time (high range), 4 Full-Time
(high range), Nuetral, and 4 LO (low range).

Yup, near as I've been able to determine, I've got an AMC 360 (5.9L) V8, a
Chrysler 727 auto tranny, and an NP-229 xfer case with d44 diff front and
rear (with 6 bolt wheels).
My transfer case controls consist of a slide switch on the dash with "2wd -
4wd" selections and a lever at the base of the seat with "HI-N-LO" with, of
course, the warning not to try to shift into LO and 2wd at the same time or
you will break stuff.
Jeeps are like a box of chocolates...
TJim

"Jerry Bransford" <jerrypb (AT) cox (DOT) net> wrote