I have a 2007 Four Winns with a 3.0 GLP-E VP engine. I just bought the boat. When I turn the key to the run position (engine not even started yet)...the temperature guage jumps from 0 to 170 degrees. As the engine warms up, the temp guage increases to over 200. The engine and some hoses are warm to touch, but not hot. The overheat alarm does not come on...except at startup test as it is supposed to. Is there a way to test the sending unit and guages? Any ideas? Thanks