5-30wt. mobil 1 . synthetic . walmart I have seen $26.00 5 QT container. using 5-30wt in winter and this is the recommended oil, the starts in below 20 deg f are very good.. you can see a slight difference with the 10 -30 wt oil on cranking at temps around 10 deg f... where you live using the 10-30wt would be of no help with higher temps .. are there trucks down your way with oil coolers aftermarket installed ?