AMEchambers

So after a horrible experience... Shearing a rear pinion gear, axle leaks, no car for a week etc... I finally got it right! I have completed the break in period and I need to change the oil from what I hear. Should I still use the 75w90 like my manual states? or should I go with a heavier weight? What are yall running? BTW this is my dailly driver and it does alot of long trips on the highway if that matters. Thnx

u-joint

For break in I used a conventional oil... not sure what weight, the shop that installed my gears put it in for me.

After about 700 miles they inspected thing, and I brought my own 75W-140 Mobil 1 for them to fill it with. I've been running 75W-140 Mobil 1 ever since

jeepjackal

I thought royal purple was the best for the engine and gears, tranny, etc....

joe002

If you are going to tow then 75w-140, otherwise the 75w-90. I use Mobile 1 for my diffs.

u-joint

Ok... call me ignorant... but if 75W-140 is good for towing, wouldn't it be good just in-general for a Jeep that sees off-roading?

joe002

The 140 is thicker, so when you put that added pressure on the gears when you are towing you keep oil between the metal (because the thicker oil will take more pressure before allowing the metal surfaces to rub).

If you are just wheeling you’re not constantly pulling on the gears like you do when you are towing. I’m sure you can get into some circumstances where you add pressure to the gears, but not like you do when you are towing a couple thousand pounds or more over longer distances - including up hill.

Another note. The 140 will get a little hotter than the 90 when driving. The extra heat doesn’t help anything, but if you are towing you need the extra protection from the added pressure so you have to use 140.

When I got my 5.38s I verified what oil to use with the owner of the shop. He said the same thing - towing use the 140, otherwise stick with the 90. The Owners Manual says the same thing.

u-joint

Thank you

Thats some really good information. I guess I've been running the "wrong" oil for my circumstance, as I NEVER tow. Next oil change I'll switch it out, especially with summer approaching.

joe002

I know lot’s of people (myself included at times) that want to put in thicker - thinking it’s better, and at times it is. If you aren’t towing there’s no real benefit, and by using the recommended 90 which isn’t as thick or as hot as the 140 you may potentially possibly see a slight uptick in MPG.

Fasttrack

Royal Purple - 75/90

I have put this in after the break in period on all my vehicles for years since I came across the stuff.

Seems also to be the go too type for a lot of wheelers here in FL.