worth pointing out that all oils are detergent, unless you specifically get a straight mineral oil - I think it depends on wether the engine has been run w/ or w/o a filter since new and what oil has been used in the past - if the trucks new-to-you then most likely it has been using the standard 10-30 for decades, and no reason to not stick to that in your climate for normal use - doesn't hurt to add a filter if there isn't one, but for my money the best policy is simply 10-30 w/ frequent changes and watch the oil pressure!
multigrade oils are designed to work at all temps - they act thinner when it's cold, thicker when hot - straight weight oils get too thick in the cold, thin too much when hot - if you have really hot summers then maybe 10-40 in the summer, 10-30 winter
Bill
