I personally like Marvel Mystery Oil for cleaning internal gunk as well may be your problem. The stuff is great for this application. I bought a "Mount St. Helens" truck with oil consumption problems, 3 qts on a change @3K, and MMO brought that down to 1 qt @3k change usage. Add a qt of MMO when you change the oil and it will help a lot with dissolving the gunk inside your motor, including carbon deposits.
dg
