I have a 1997 F350 and want to change the fluid in my T-Case. Is going to synthetic like Royal Purple a good choice? I am used to old school NP 205 cases so I just want to make sure there are no compatibility issues with changing oils in this style case. Any other recommendations on oil choice? I do not use the truck in severe off road conditions just a daily driver.


Brian

 

if i remember correctly that uses regular old automatic transmission fluid in the transfer case.

 

Yeah, the owner's manual for my '97 F-250HD calls for ATF. I suppose a synthetic ATF might be a little thinner at really low temps if that's an issue, but ATF isn't very thick anyway, so I don't bother with synthetics in Minnesota winters.

 

What would be the downside of using 80-90 weight oil in a 205 T-case?

 

The NP205 pretty much went away (at least as far as new vehicles were concerned) in the '80s, so we haven't been talking about them.

But back when they were being used, I believe that something like 85W-90 was recommended. So I don't think there'd be much of a downside to using the recommended lube.

Although I think I remember the old-school cases switching to ATF in the last year or two of their use. I don't know for sure that ATF was ever recommended in the NP205 specifically, but it wouldn't surprise me if it were. I believe the change was for fuel economy and I don't know if any changes were made to the 'cases that switch to ATF or not. I'd guess not, so even 'cases that did switch to ATF at the end I think could still use 85W-90. But I'm not at all sure of that.

 

agreed. gear lube in a 205 will not do any damage. and if ht ecase is an original with high mileage, it may make it quieter out on the road.

 

The old rule of thumb was look at the case material, if it's cast iron use 85w-90 is it's aluminum use ATF.


But I believe the OP's original question was using synthetic fluid. Sure go ahead won't hurt anything but your wallet. Won't help much either but if it makes you feel better shouldn't be an issue. Just be sure and get ALL the non synthetic fluid out, and I do mean ALL of it. Bet to only do it with a newly rebuilt box.