10k5884 Serial D333C

I have a 71 D6C, when I got it leaked from hydraulic tank. The previous owner put regular ol hyd oil for a tractor in it. I have not used dozer in a couple years and a majority of that fluid has leaked out. I have searched and searched and cannot find anyone that agrees on what goes in this machines hydraulic system. I have an old timer telling me to put rotella engine oil in it, and I have read where people use trans oil. What do I need to put in there that is right, I do not want to tear the machine up. When I go to CAT for parts they have a hard time finding any info on machine. I have all the manuals but they are at my property a couple hours away and CAT is 10 mins from my house. Id like to just buy what I need from them tomorrow and be on my way. Any help is appreciated, but I prefer someone that is familiar with this machine.

I was using Cat 10W hydraulic oil for some years when they came out with it, before that my dad would use Shell 10W engine oil for the hyd. My oil distributor told me the older 10W is what you should use in the old vane type pumps, he recommended Phillips Power Drive 10W hydraulic oil, I asked about AW46, he said no, Cat oil is thin like AW oil also. But everyone you talk to has there own opinion what to use.
shop.sclubricants.com/phillips-66-powerdrive-fluid-10w

Where y0u are at wil help also. Are you in a cold climate or not?

discussing lubrication and oils is always a slippery slope on a forum...here goes...

-all oils presently on the shelf are likely light years ahead of what was available when equipment was new...
-not a fan of high buck, high hype, highly promoted highly advertised lubes....esp synthetics...
-if i was in Texas, i would buy the cheapest oil i can find, in jugs or pails.. probably 10 or 20 weight etc
-look for the API donut on the label....SL, SN etc....that's the certification that counts

Im in Texas, temps between freezing and 105. mostly 80s-90s

Hi Dutchboy, I had a 'dozer contracting business in Texas for 23 years. I ran D6Cs, D6Ds and a D6H.  I used Texaco Ursa Series 3 engine oil in the hydraulic systems of them all. 10W in the machines when new and 30W when they were higher hours.
The "Tractor Fluid" oils are cheaper, but you get what you pay for. I have a friend that is still in the business here (D8K & D7G) and he says the cheap oils don't perform well in hydraulic systems in the Texas heat.
I still think the single weight oils are best for this application, You can always mix 10W and 30W of the same brand oil to come up with a in between weight if you want.
Craig
 

Hi Neil, These days I use Chevron Delo single weight oil, I find it in gallons at many sources here including O'Reilly's.
Craig

 This is what to look for, it is also available in 30W. I use it in our D7E and D6B. 
 
Craig

Do you actually know whats in that oil? or just assume "its good enough" because its Delo? Most oils today are for the "new" style engines not for the older engines which require different specs.