A few days ago the thermostat in my Civic apparently decided to stop working in the "open" state. So now I would estimate that the coolant temperature is maybe 100-130 degrees, depending on the outside temperature and how fast I'm driving. Besides having no heat and getting bad MPG, are there any problems with operating the engine in this condition until I can get a nice warm day to work on it? Or should I just pay someone the $50 to install the new thermostat? BTW, I've got 5W-30 in the crankcase right now.