I have a 1979 Searay and it overheats after I run it for about 10 minutes (not in idle). It's a Mercuiser, inboard/ outboard
and it is open system. Do I NEED a thermometer in it? I ran it with one in it the first time and it overheated melting all my hoses. I found out it overheated the first time because I needed a new water
pump. I bought a new water
pump and hoses. I took it out to the lake without the thermometer and it over heated again after 10 minutes. Seeing I have an open system do I need a thermometer? If so, is there any other solutions why my boat is overheating
. I read the other postings and I have already checked everything.