I have twin 1994 175 hp mercury black max both run great but after replacing the water pump and stats . the starbord is running fine, the port warms up like the starboard but then the port side goes cold . I crossed gages and no difference switched stats no change I can put my hand on the head and its cool the starboard too warm to keep hand on.Good water flow from the pisser whats going on . could the poppet valve be stuck open and cause it to run cold ?