had a similar experience with the nt16 myself... I got fed up and went with the os 18..... a while later I picked up the 18 conversion parts but never got around to breaking it in... The overheating I had was due to the junk fuel tank on the truck and not the engine... The plunger would lean out the engine causing it to overheat... I'm not truly convinced that my engine was ever bad, but the os 18 has sooo much more power... Still have the cen "18" sitting on the bench waiting for a new home..... Not even a breakin tank yet...