If it were me, I'd do it every six-months with a name-brand 5w30 mineral oil under current driving conditions...
But, have you considered taking an old fashioned Sunday "motoring" and taking your truck out for a few miles on the highway and doing a little site seeing? I think you'd get rid of some of the accumulated impurities and could go a full year on a mineral oil in good conscience this way...
But, have you considered taking an old fashioned Sunday "motoring" and taking your truck out for a few miles on the highway and doing a little site seeing? I think you'd get rid of some of the accumulated impurities and could go a full year on a mineral oil in good conscience this way...