A hotter engine is a cleaner engine. oil stays decent, dosn't sludge up as much/ fast, so it can keep everything cleaner. not to mention a hotter engine burns cleaner ( less carbon ).

I just did a head gasket on my grandparents '95 Plymouth Voyager van engine ( 2.5 4cyl ), it has a factory 195* Tstat and low tension rings. it has 172,000 miles and the cross hatching is still visable. has no ring ridge ither. it runs CLEAN.