· Premium Member
Aaaah, the creeping temp gauge and admittance to changing the fluid recently. This sign is a real case of an air bubble in the engine side of the system. Your overflow may be filled properly but there is enough air in the engine side that it isn't able to expand the fluid when warm enough to push the air out and pull fluid back in its place. Try parking on an upper angle when cold, pop the cap, see what the water level shows. If low, fill more and try squeezing and pushing the upper radiator hose so more fluid goes in, cap it when the fluid is full to the top of the cap edge. If this is not the case, which I believe it is, then the radiator cap itself isn't holding pressure properly and allows the temp to go up, hills because you are on the gas more, thus cylinder temp rises.