I had the same problem w/ my RS. Replaced the thermo, replaced the radiator, did a flush and fill. No matter what I did, it kept coming back to haunt me. When I put a system in my car it got worse. Every time the bass hit it drove the heat up a tad. Turns out I had a bad alternator(seriously!). The thermo wouldn't open, making it overheat in idle(and causing the hose to rupture). Not saying that's what's wrong w/ urs, but it happened to me...