thicker the oil(less viscous), the more likely it is to gum up in the lines. I personally think 10W-30 is fine even in your conditions. It works fine out here and it is hotter than hell in the summer and plenty damn cold in the winter. Mobil 1 synthetic for me but only because it is readily available at a decent price. Redline, Amsoil, Royal Purple all great oils but they just might be a bit of overkill for daily drivers, imho. If you really want an expert opinion, I would contact the oil mfg. and see what their engineers recommend for your specific situation.
