I use the 75W140 rear diff lube since I tow occasionally and I change it every 12.5K miles. Now some posts indicated there is a mileage penalty for using this lube Vs the lighter diff lube. How much fuel penalty is there for this? Does it matter a lot less if I live and drive in a warm area? Isn't the frequency of the lube change a bit crazy? I remember changing these maybe once in the lifetime of other cars & trucks I have owned. And this is expensive synthetic stuff, seems like it should last forever.

There have been threads on this - search around. I run Amsoil 75W-90 and I do some light towing (6x10 covered motorcycle trailer). I have a PML diff cover which adds some fluid to keep temps down (and a drain plug). With the synthetic fluid I am planning on 30k fluid changes. I don't take it off-road so could probably go even longer.

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Chris
Current:
2007 Steel Blue Metallic Grand Cherokee CRD Limited
GDE Eco Tune and DPF delete
CB Engineering DPF delete pipe
EHM

Past (sold to Mountainman):
2005 Patriot Blue Liberty CRD Limited

Frank I think that mileage change interval is excessive even if your towing. My experience with the 8.25 rear end is that its pretty sturdy and takes a licking, the newer 29 splines like our old XJ and KJ have are nearly as strong as the D44(very very closely rated).

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http://www.Colorado4Wheel.com
"Its not about what you can DO with your Jeep, its about where you can GO with your Jeep."
Knowledgeable - But Caustic