My engine has suddenly started running much colder than normal. Under highway speeds the temp gauge sits at the "L" in NORMAL. When I get off the highway the temp gauge goes up to the "O" or the "R". One instance it went up to "N". My SHO didn't do this prior to my Y-Pipe install on Tuesday. I'm guessing it's the thermostat going bad. What else will cause such rapid temp fluctuations? Thanks guys, Ken EDIT: I have checked coolant levels and everything is OK. No oil in reservoir tank either.