So I've had my 08 Sahara Unlimited since new in May of 2008. While I am usually on top of keeping all my vehicles maintained as scheduled alot has happened since I got my JK (my wife and I had our first Child, changed careers, presently unemployed etc.) So I have been neglecting my Jeep a bit. Anyway I've never actually changed the diff fluid on my JK although it has been done by the dealer as part of repairing leaking axle seals. So the front axle seals were done at 29k rear at 33k and then both front and rear again at 42k. Just yesterday with 78k on the odometer I drained both front and rear and filled em up with Royal Purple 75w90. All I can say is WOW what a dramatic improvement!! The royal purple bottle says maximizes horsepower, and fuel efficiency, which may not be a noticeable feel to most who have maintained there Jeeps properly but for me it feels as if I'm running a supercharger in comparison to how it was. I guess because I drive it so much I never really noticed a change when it was running sluggish. But no BS it feels like i've picked up 30% power increase.

When I drained I did not remove the diff covers I just removed the drain plugs and fill plug. But I think I'm gonna drive it around for a week or so and then do it again because when I drained the front I barely got out a quart and could barely fit a quart when filling the front.

The rear gave me just over 2 quarts when draining and took just over two to fill. But either way I think I am going to let the Royal Purple run through and mix with whatever old crap is still in there and then next week remove both covers and really clean em out then re-fill.

I'm sure most people realize the importance of changing the diff fluid, but I just wanted to write this if there is anyone on here who like me has been neglecting this portion of the vehicle maintanance, trust me it is necessary and soooooo worth the 85 bucks worth of gear oil and 20 minutes of your time.

Acceleration is super smooth now, and it has a ton more pickup, although I haven't put to many miles on since yesterday I know that I will see a dramatic increase in gas mileage. Last night I was on the highway cruising at 65 with cruise control on I reset the gas mileage and I was holding 19mpg prior to changing the gear oil I was lucky to hold 15. I thought that it was due to bigger tires and lift, never considered it was my gear oil.

Anyway just thought i'd share hope this helps someone. Next up is ATF and transfer case. Oh yeah gotta changed my rusty exhaust system and my clogged catalytic converter also. I should be getting like 25mpg in no time lol (not likely it's still a box on wheels)

 

Remember! That oil is to light for towing.

 

JK-Ford, what you recommend to use if one was towing?

Thanks

 

75w-140 in the rear for towing. (if you have Trac-lok you need the additive)

 

and keep 75w90 in the front?

 

wow...good report...didn't expect those benefits...
i'm looking forward to mine...in 2500 miles...

 

i should probably to that. Dealership wanted $85 per diff. Looks like i have another item on my spring to-do list.

Current list:
fight to get oil leak fixed
align front end
shorten control arms
get leaking valve stem fixed
change differential fluid
set-up CAI
powerwash under neath
repaint muffler
clean inside and out


Don't youh ave to add an additive if you have limited slip rear axle? -found it nvm.

 

No BS huh? Yeah right.

 

what oil weights are people using in their Tcase and tranny (manual)?
time to change mine is fast approaching.

 

yup, unless... are you towing in 4wd?

t-case gets the ATF+4

can't say about the manual as I have an auto...