Any downside to 75w-140 v 80w-90 in a differential?

Hmm … my rear axle is M220 …
So is mine and 20mm hardly discounts the need for higher viscosity oil when operating under higher loads. Based upon my UOA results and operating temperatures, there is no way I would run anything less than 75W-140 in it.
 
So is mine and 20mm hardly discounts the need for higher viscosity oil when operating under higher loads. Based upon my UOA results and operating temperatures, there is no way I would run anything less than 75W-140 in it.
Hard to understand why the OM is written that way but I found my last Ford OM to be a Waldo search too
Did find many owners are doing it (spotted you on another site) … and a bit surprised with the low capacity as well …
So, purchased Valvoline SynPower 75w140 for the rear. (2 for $20 sale at AZ)
… still have some M1 & Delvac 1 … so will use one of those 90’s up front.
Thanks …
 
Hard to understand why the OM is written that way but I found my last Ford OM to be a Waldo search too
Did find many owners are doing it (spotted you on another site) … and a bit surprised with the low capacity as well …
So, purchased Valvoline SynPower 75w140 for the rear. (2 for $20 sale at AZ)
… still have some M1 & Delvac 1 … so will use one of those 90’s up front.
Thanks …
FCA reduced the capacity from the JK Dana axles to the JL series as a carrot for CAFE. The JL axles are also Dana Advantek (https://spicerparts.com/parts/axle/automotive/advantek-axle-technology) and not the same as the previous generations. The low(er) capacity and higher operating temps is what I based my decision to use 75W-140 on--the Valvoline is fine and you cannot go wrong with it.
 
My 2009 F150 axle spec was 75w140. My 2016 F150 axle spec is 80w90. Both have the same max tow 9.75, 3.55 rear axle. My 2016 got 75w140 at 20k miles. Probably a slight benefit to EPA numbers for the hot 90wt.
 
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