Originally Posted By: ericthepig
Here's a touch of anecdotal data -
My '98 Sienna is apparently known for heat issues. I bought it at 62k miles (apparently very well maint.). I ran the various M1 regular lines in it for 80k (max 9k OCIs, typical was 8k, a couple of 4k w/ 0w30 over the winter months). Toyota mech was in the engine (valve cover gaskets & timing belt) at the end of this 80k run. Said engine was clean. Fine. However, I had significant oil consumption w/ no obvious source. Discussing this with BITOGr (toyota mech) Mokanic - it's apparently gummed oil rings. Mokanic said you can have a clean engine, but gummed rings. So M1 may run clean, but it apparently didn't stave off ring deposits.
1) Rings don't gum up, they can carbon up which leaves the rings incapable of expanding against the cylinder walls allowing oil to pass by and losing compression.
2) M1 5-30 is very good at resisting heat deposites( Hondas HTO turbo spec)and the area around the top rings is some of highest heat parts of the engine. Without pulling a piston there's no way to know about stuck rings except maybe a compression test.
3) If the rest of the engine is that clean and you do have carboned rings there must be a serious design flaw for your type of engine.