Gear Oil for Dana 135?

[dogememe]

This is in an F-550, currently it's a bucket truck but I'm in the process of selling the bucket and boom assembly off it so it'll basically be a normal utility truck. I don't really ever tow or haul stuff.

Trying to change out all the fluids front to back since it's been sitting for years and the previous owner didn't ever do any maintenance on this truck lol.

Ford simply specs GL-5 80W-90 for this application but according to Dana for my ambient temps any of the following would be acceptable: 75W-90, 75W-140, 80W-90, 80W-140, 85W-140.

Here in the SF Bay Area it doesn't really get cold so I understand that I don't need the cold temperature benefits of synthetic, but I prefer going full syn for everything. Only reason I'm not running full synthetic engine oil is because it was out of stock when I did the oil change lol.

I'm thinking of either using the O'Reilly MasterPro 75W-90 or the Mobil1 Delvac 75W-90. I do get a discount on the O'Reilly stuff but I'm not sure if it's worth spending extra to get a "business class" gear oil like Delvac? Or should I scrap the 75W-90 idea and go with a 75W-140? I'd prefer the additional fuel economy of the thinner oil since I don't tow much but I also want to make sure I am not damaging the differential as if it goes bye-bye the truck is pretty much scrap.

Any and all input appreciated

 

[BituminousCoal]

Mobil delvac 1 80w140

 

[dogememe]

Mobil delvac 1 80w140

Why

 

[BituminousCoal]

Why

Great extended drain gear oil. used in otr apps extensively, racing apps, and helps hold together offshore outdrives when few others can. Also reasonably priced compared to other hi performance oils. (when purchased in 5 gallon pails)

 

[zrxkawboy]

Personally, I’d probably use the Mobil 1, but either of your options would likely work just fine.

 

[CarbonSteel]

Given the workload this truck will typically see as well as the moderate climate in which it operates, I would go with a 8xW-140. It is cost effective against a comparable synthetic, it is very robust, can handle higher temperatures without losing much viscosity and does well with shock loads. Based upon what I see online, this axle takes 3 gallons of oil (11.6L) and thus unless you have some operational condition to use a synthetic, I would save the $$$.

 

[tcp71]

Redline 75w140 should last the life of the vehicle.

 

[dogememe]

Thank you all, some great information. Unfortunately today I sold the truck.

 

[benjy]

i switched from the 75-140 nissan semi syn mollasses to redlines real synthetic 75-90 as noted in the dana web article