Rear differential LS additive?

[Afsigma21]

I am getting ready to change my differential fluids, I do have the electronic locking rear diff.

Do I HAVE to use the Motorcraft 75w85? I am sure I can use 75w90GL5 without issues.

Do I need to add an extra bottle of friction modifier like: https://www.amazon.com/dp/B00J0G09JW?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1

Or just a fluid like this with the additives already in it?: https://shop.valvolineglobal.com/pr...rzffOA14CE5cgnlFrZvlhGKBQTObZdfOuxT&Size=1+QT

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[RB205]

Lockers aren't limited slips. You don't need the additive but it also doesn't really hurt if you use the Valvoline with it already included.

Run the gear weight you want. Dana recommends 75w140 for these M220 Advantek axles. That's what I'm planning to run; Ford just recommends lighter oil for better mileage.

 

[Afsigma21]

OK, Using same thread for a newish topic related.

Looks like we have Dana M220 which Ford calls for 75w85, but Dana calls for 75w140 for HD situations like towing.

Prepping my truck to tow a camper from Ohio to Alaska and back. Differential fluid before the trip is a 100% item, I was going to go to 75w90 Valvoline, but now I am considering 75w140 since I will tow approx 10k miles on the trip.

Replacing upon my return with 75w90.

I would love to hear some thoughts on the 75w140?

 

[MasterCylinder]

OK, Using same thread for a newish topic related.

Looks like we have Dana M220 which Ford calls for 75w85, but Dana calls for 75w140 for HD situations like towing.

Prepping my truck to tow a camper from Ohio to Alaska and back. Differential fluid before the trip is a 100% item, I was going to go to 75w90 Valvoline, but now I am considering 75w140 since I will tow approx 10k miles on the trip.

Replacing upon my return with 75w90.

I would love to hear some thoughts on the 75w140?

The debate on 85/90 weights verses 140 has been going on since it's inception. The main reason for the lighter gear oils was Fuel mileage gains however slight to meet government standards.
Little information for you to ponder on.

Grade	SAE 75W90	SAE 75w140
Density 15 C, g/cm3, ASTM D4052	0.86	0.89
Flash Point, Cleveland Open Cup, °C, ASTM D92	210	203
Kinematic Viscosity 100 C, %, ASTM D445	15.7	25
Kinematic Viscosity 40 C, mm2/s, ASTM D445	115	182
Pour Point, °C, ASTM D97	-45	-45
Viscosity Index, ASTM D2270	144	170

The flow is measured through a viscometer at a certain temperature according the ATSM standards.
All rear axles gear teeth are setup the same with a certain degree of what is called back lash so that there is no whine from being too tight and space for the gear oil to get in between and lubricate and protect the surfaces form heat and wear. The lighter gear oils weren't commonly used until the late 90's. All gear oils contain what is called extreme pressure additives for their intended use. 90W gear oil is almost the same as 50W motor oil viscosity wise in testing.

 

[Afsigma21]

" The debate on [insert any oil/fluid/additive] has been going on since it's inception "

SO TRUE
Im leaning towards the 140 just for the trip then go back to 90.

 

[MasterCylinder]

" The debate on [insert any oil/fluid/additive] has been going on since it's inception "

SO TRUE
Im leaning towards the 140 just for the trip then go back to 90.

Just as a note, get yourself a decent Infrared thermometer. Check your temps under normal conditions and then when towing. Keep in mind today's synthetics adds a bit of protection from heat over conventional and from experience anything over 250F in my book is getting into the yellow caution zone for any gear lubricants. If changing it makes you more comfortable by all means be comfortable, it's your ride! A Electronic locker normally is not a LSD because it has the Electronic lock.

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