In Reply to: Re: Hydraulic Fluid Source posted by TheOldHokie on February 24, 2019 at 16:59:59:
I know I've seen the M-4864-D spec somewhere but the 600/800 Operator's Manual lists it as "Mild Extreme Pressure Lubricant SAE 80" for both summer and winter. In the oil story by Llamas, he says the M-4864-D spec is the equivalent of GL-3 spec'd oil, which, I think, just means has more sulphur and phosphorous properties in it. All the OEM Ford manuals state to change out oil viscosities on both engine and hydraulic oils, whenever the wind changes direction, well almost. I highly doubt very many farmers conformed to the manual specs especially in climates where it could be -10°F one day and +40°F the next. I use the same stuff all year on both engine and transmission and never have any problems. I always warm up at least 15 minutes anyway before using it so don't see what temp it is matters. Even when I use to park my 8N outside in subzero temps, it started and ran fine. Thinning out engine oil with mineral spirits may help some in the extreme cold, but I never did that, and I use SAE-30 detergent all year.