BITOG: What causes sludge?

I would use a 10W-30 HDEO (Heavy Duty Engine Oil) like Shell Rotella T4 (CL-4/SN) in your engine. The detergents in HDEO will slowly clean up the deposits in your engine. Brad Penn makes a 10W-30 HDEO (CI-4/SL) too.

Engine Oil Article
Sludge Article