I have only been unable to find a few cases with real data for cleanups using motor oil. Real data like independent teardowns before and after with different oils are hard to find. Just claims by the manufacturers and the users. I have been reading along on multiple forums looking for this, sorted out those who claim something with no proof other than what others say or never used the product from those that attempted to prove a cleaning claim. Here's a small summary:
Read a lot of threads about subie turbo enthusiasts using T6. They claim the oil holds up better, makes the engine quieter. Some on here claim a HDEO cleans better, some posts here claim disappointment. More claim oil consumption stayed the same than improved. those that used the thicker t5's claimed an improvement in consumption which makes sense, its a thicker oil, less flow, etc. I used T6 in an old corolla as a test. It definately ran quieter, smoother. No clear evidence of any dramatic cleaning. A little varnish on the stick remained, but it did clean a lot of it off. Oil got a little dirty, but not that bad. IMO avg cleanup, would be good as a prevent.
Reading oil consumption or cleanup threads the Castrol products, GTX, semi blends, etc. are commonly referenced as the oil that had been used. While it never gets the blame for dirty engines, theres no disputing that oil is mentioned quite often. In another forum I have followed a High Mileage teardown and rebuild (320k) for an oil consumption problem. Oil used for the majority of its life was Castrol Syntec blend @ 5k OCI. Upon teardown all the parts were good, no wear, but the engine had a bad case of varnish and a fair amount of deposit buildup on the oil control and scraper rings. The varnish that clogged the piston oil return holes flashed and hardened into a carbon mass. Cleaners were used on the piston after it was removed from the engine. Nothing could get it out, the holes had to be drilled out. The vvt-i controller was also stuck with deposits causing performance issues. It had to be completely taken apart and cleaned. So although Castrol syntec blend gave the engine a long life, would appear the oil choice caused the consumption problem.
Lot of claims about the power of Pennzoil as a cleaner. Is it hype or for real? Going to find out. I'm currently running PP in one of my cars, a synthetic convert. Not very dark so far, still has varnish on the dipstick at 4k. The engine was definitely dirty prior to PP. Oil was horrible looking, varnish on the stick, PO used OLM for OCI's on unknown dino. Have the service records. Lube shop dino. So..Pennzoil cleaning power inconclusive so far.
I'm currently using Mobil 1 High Mileage full syn in another troubled engine. Seal and gasket leaks, sludge and varnish from a PO neglected dino life. Went to maxlife first. Was an ok oil, appeared to be cleaning pretty well, but the varnish on the dipstick remained after 2 OCI's. Then I made the switch to M1 HM after reading the product sheet that claims "extra" cleaners. A ton of deposits came out after the first 2 oil changes. Chunks of sludge, other small particles. varnish on the dipstick was gone after the second OCI. Idled better. No leaks. I stayed with it. So IMO M1 HM is better than maxlife semi in more than one way.
The engine running M1 HM was staying fairly clean throughout a 7k OCI for thousands of miles. I added Kreen after reading about it on here. Boom, dirty oil fast again. Why was it dirty again? I can only tell you what the dipstick looked like. Dirty at 4k. subsequent OCI's with M1 HM/no Kreen - oil stays clean for the entire 8k OCI, so I "think" it helped even further.
So there's a small amount of data mixed with my own trial and error. Hope its useful.