Years back I did what my old man did on all his cars.Add a quart of kerosene at change and run at idle for like 15 minutes.Then drain install plug pour in another 3 quarts.Drain refill with new oil.The old man had the 55 for like 10 years and it had well over 150K when he sold it.Ran like new.My 47 Plymoutyh and others were all super clean inside and never had engine problems.With new oils its really not needed if changed regular.I do mine evey 3K miles.Oh yeah quaker State I used till I rebuilt 1 440.Changed oil every 2K on it.After 6k miles pulled valve covers and it was getting sludge.Went to Kendall and Valvoline and Castrol.No more problems.RockyI