Hey there, just wrapping all the little things to get this truck to daily driver status. She drives great and have tackled most things. She has the NP435 and the Dana 24. I have been reading up and wanted to confirm as I am seeing different recommendations. I know Ford recommended straight 50W engine oil so I was looking at this one below, looks like it is a synthetic blend.


Others have said to run 80w-90. Wanted to confirm if there is a preference and if so why. The car is probably going to be driving around the Las Vegas area the next year or so as I will be spending a good chunk of time out there so it will be hot outside compared to the California Coast. Thanks in advance.

 

50w was for weather where you wouldn't see below 10*f temps and 30 was if you wouldn't, but that was until 1972 then after they recommended 75w80 in cold temps and 75w90 in warm.

I would personally choose rotella t1 50 if it were me, but that valvoline will be fine too. i know quite a few people that run synthetic 75w-90 in their old heavier duty 4 speeds transfer cases and diffs. the only reason I'd be cautious to do that is if i had even the slightest leak or weeping because synthetic is going to be able to squeeze through places that mineral oil types wont. nice thing about that is you can get it in a bag so it's a lot easier to squeeze in than deal with bottles and/or pumps

 

Man this Rotella T1 in 50W is hard to find unless it's straight up 5 gal buckets. Everyone has the 30W, I will see if I can track this down. They do offer it in 40W, wondering if that is the way to go if I can't get the 50W.. Would like to stick with the 50W if possible versus the 75w90.

 

Wound up going with the Royal Purple Max Full Synthetic 75W-90 and it shifts like butter. Great stuff and well worth it in my opinion. Of all my cars, this truck is the only one that doesn't leave a drop on the ground where it is parked. I don't know how because it is a driven and beat up farm truck. The transmission had engine oil in it for sure. The transfer case, I could not tell at all. It looked like chocolate milk/coffee coming out of there whatever it was. Didn't have a sulphur smell to it or anything. Anyway they are rock solid and good to go now. I need to find time to knock out the knuckle seals as the felt and rubber seems to be pushing out some grease here and there as I drive it.