We use 30 wt non-detergent oil.Reasons: constant viscosity,constant lube characteristic.Multi vis {10-30} changes w/ heat.Detergent oils break up deposits and may cause clogs.We have a lot of owners bring cars in that have the wrong oil{as well as the other o/d issues}.We also use kerosene to clean out old gunk {about a quart or so,twice} in really bad cases.Many times we find that the solenoid needs cleaning or adjustment,and the kickdown switch as well.Take care refilling on a level surface,don't over-fill.Best of luck ...