Can gunky oil be cleaned inside the motor?

If your oil is gunky change it but there is a whole market out there for sludge protection castrol motor oils are top of the line and you can go even further by adding products such as marvels mystery oil, z max or any other number off additives

A good way to clean out the sludge in your engine is to add a small amount of Diesel to your engine oil (between half a litre and a litre) and drive normally for a couple of hundred kilometres before changing your oil & filter. Diesel has excellent lubricating qualities so will not cause any damage to engine internals, and will effectively break down sludge.

yes. its something like $60 at a quicklube or jiffylube to get it done. im not sure what they do but they do an "engine flush". gets rid of all the gunk built up. instead of these additives and what not just go get the engine cleaned out and then use high qaulity oils afterwards. plus some gas companies have certain additives that help prevent build up also such as nitrogen enriched shell gas and bp with invigorate(sp).