i have a 97 f250 7.3 & 5 spd & it has 350000 kms . i want to change all fluids to synthetic . what weight of oil would be best for : engine , tranny(std) , & front & rear diffs ?
Use the syn replacement for the tranny and rear & front ends. The motor oil is your choice, but it looks like 5W-40 would work in your area. I use it here near San Francisco, Ca.