Thank you all for the help and advice. Be advised that I purchased a digital infra-red thermometer. I ran the boat in the dock and the gauge...
Engine was recently overhauled! hence new pump and clean water ways!
Thanks for the input, unfortunately I have taken off the engine driven water pump and it looks like new! V2climb
I have a 1978 Seay Ray SRV220 with Mercruiser 260HP. I have serious mystery overheating! My temp gauge slowly rises whilst underway until it...