I would use a straight weight detergent oil and change it after running until hot, and then again after a few hours. change the oil as often as you can afford for a while. the detergent only keeps the dirt suspended for the filter to remove. detergent oil is marked as HD. Non detergent is labeled as non-detergent. Detergent oil has other additives that are good for your motor.

"It ain't a truck if you can't hose out the cab."