What gear oil to use...75w90 or 75w140??

[DHerzog]

I think I read there was a TSB on the rear end gear oil... the owner's manual says 75w90 synthetic, so I bought 4 quarts of Royal Purple to do the job... BUT, does the TSB say that 75w140 is OK to use or is MANDATORY? I tow a 5th wheel a couple of times a month on short trips... less than 200 miles round trip usually.



Any help would be greatly appreciated, as I am planning to change the oil this weekend... thanks Oo.

 

[gonzo2]

75w90 is just fine.

 

[JayB]

Does anyone know how much gear oil I will need for a 3500ls rear? I just got a Mag-hytec cover. Thanks, Jeff

 

[red-rider]

Hey JayB,

I have the 2500, on the 3500 I believe your axles are alittle thicker then mine, I installed my MagHytec cover and I purchased 9 quarts I ended up using only used 8 quarts though. So hope this helps. If worse comes to worse you can always call MagHytec and ask for advice on how much to add.

 

[JayB]

Hey JayB,

I have the 2500, on the 3500 I believe your axles are alittle thicker then mine, I installed my MagHytec cover and I purchased 9 quarts I ended up using only used 8 quarts though. So hope this helps. If worse comes to worse you can always call MagHytec and ask for advice on how much to add.

Red-rider, Thanks for the info, I'll start with 8 qts. Jeff

 

[DHerzog]

I thought about the mag cover... I did not realize it added so much extra capacity... would it be correct to assume that 75w90 would be ok even hauling heavy loads since there is an excess of oil (remaining cooler???)

 

[Heavyweight]

With increased capacity,,,, 75w-90 would be the perfect choice... . If I pulled a lot of weight,,, I would consider the thicker gear oil as an option in summer time...



I would only run Red Line NS -- Amsoil or Royal Purple... . The premium synthetics in the pumpkin is the way to go... .



http://www.redlineoil.com/products_gearlubricants.asp?pvID=84&prodID=60&subcatID=20

 

[mberry]

I have to agree with Heavyweight. With that much capacity I would use the 75W-90. I am using the 80W-140 RP in my rear diff right now simply because it gets so darned hot here in the summer and I wanted the extra protection while towing in this heat. I have had no problems with my choice of gear oil.



No matter which oil you choose to go with, make sure it is GL5 rated.