Hello, I have a 00 XJ that's got a 3" lift and 31's. I'm going to get my axle seals replaced tomorrow and like synthetic fluid. I have 3 old bottles in my garage (purchased approx. 3-4 years ago) of Royal Purple 74W140. It's still new and the seals were never broken. Will this suffice for my front axle or do I have to use 75W90? I'm going to be towing a small U-Haul in a couple of months cross country on my move if that matters.

Thanks in advance.

 

I would go with 75-90 for the front axle, you probably won't be pulling your trailer in 4x4. I would use the 75-140 in the rear diff. but not the front.

 

I mixed them. I put one quart full of 75-70 in the front with the rest 75x140. It's what I had and it was all Royal Purple Synthetic. I should hopefully be just fine. I'll be in a cool climate pretty much all year.

 

great question. i was going to ask the same thing..

so 75-90 front and 75-140 rear for a sport 4x4 99, ? thanks for the assitance..

 

75w140 synth is recommended for the rear when you do a lot of towing or offroading. In other words, 75w90 is light duty lube, 75w140 synth heavy duty. It has a higher shear strength and greater longevity (extra good if you have a limited slip). Most people don't drive around in 4WD making the front axle light duty. That said I think it's fine to put 75w140 synth up front, its just more expensive.

 

I haven't personally used it, but I think Amsoil makes a 75W110, if you're looking for a "happy medium". Like I said, no first-hand experience, but I believe that Amsoil makes quality lubes.

 

Just out of curiosity what are the downsides of putting 75w 140 if you dont haul a trailer?

 

No downside unless you have to pay more for it.

 

Any 75w-140 Synthetic Gear Oil is fine for both front and rear diffs. Scamsoil, I mean Amsoil Severe Gear 75w-110 and 75w-140 would be fine choices, but I would personally go with Mobil 1 75w-140. I dont think Jeeps like boutique(hard to get, UnCommon) oils. Jeeps are hard working, everyday working people vehicles, that seem to like Plain Jane products(ie Champion/Autolite plugs, Fram/Wix filters, Conventional oils, etc).

 

some may disagree...

 

"Boutique" oil like a gear oil that has the proper synchronizer gear friction modifiers AND isn't corrosive to brass? I have to travel 300 KM to find a place that sells that stuff. This is the closest thing to the fluid that was specified in the manual when my transmission was introduced over twenty years ago.

I think you're confusing a Jeep's high tolerance for abuse with the tight design specifications of newer vehicles. As an example, just because the AMC inline 6 ran fine on conventional oil from way back in the 70s doesn't mean that they won't see any benefit from a synthetic. This is in contrast to a modern high-performance engine like the Nissan 370z which doesn't run properly unless a VERY specific oil is used.

The newer shiny dipped platinum/iridium/unobtanium spark plugs don't work well in the 4.0 for a good reason: they don't meet the required specifications for the engine, which, especially in later years, was tightly tuned due to increasingly strict emissions targets.

As for FRAM filters... you might want to do a bit of reading before suggesting that the 4.0 actually works well with them.

 

i disagree.. i always use good quality oil and parts because the protection and durability that the vehicle gets with them is always better than using "cheap" parts or fluids..
i agree 100% with you

 

I can't say much about the XJ, but it seems to run just fine. I started running Mobile 1 Synthetic high mileage in the crank case along with wix filters and it sound great. I was supplementing a quart of marvins mystery oil at oil changes and it cleaned the crank case very well.

I remember in my old LJ (Unlimited Rubicon) back in the day, I changed out the trans fluid with Royal Purple and you could actually tell that it shifted smoother between shift points.

As of now, all the fluid in my XJ is Amsoil except my front diff is RP. I babied my XJ as I bought it in 2010 with 62k on the clock and drained all the fluid. I actually drained and changed the trans pan filter as well. From my research, the XJ had about 35k put on it in less than 18 months. I figured, she needed a complete fluid replacement. If you can't tell, I am big on preventative maintenance.

 

You are a smart man.
(keep records...when you go to sell it some day it'll really help the value.)