I'm having what I think is the opposite problem, my thermostat may be stuck closed. The bike, and '85 VF500F starts and runs fine, but once warmed up sufficiently I get a leak at one of the cooling pipe connections. Once while stopped at a light the temp gauge started to rise. Once cool and I check the coolant level in the radiator, it's full to the top in spite of the leak. I installed a new thermostat in the spring and replaced all gaskets in the cooling system. I had one leak also at a cooling pipe connection. Fixed that, but now it leaks on the other side. My thermostat is easy to access, so I think I'm going to remove and test it and either put the old one back in, or get another new one. What do you think?