I recently purchased a 2007 Audi A4 2.0T 70.000 miles on it. Within about 500 miles my coolant hose popped off for whatever reason. Light came on and I started noticing the heat rise. I pulled over and had to fill it with water to get it home to then drive a separate vehicle to get some coolant. Without draining the water I just topped it off with the coolant. About three days later the code p2181 popped up for coolant system blah blah.. i then started noticing that the temp gauge would vary in the morning with the heater on it would be at about 1/4 to 1/2 and in the afternoon it would be about the same more so at a 1/4 on the freeway. I read alot about it already assuming it may either be a sensor of the thermostat, but just wondering if possibly it over heating slightly or me mixing water into may have caused something else