gkaramalis
New member
I have had my 37' express cruiser with 2xD4-300 engines since 2008. After the first year I noticed the port engine coolant temperature indicator to rise from the normal 85 degrees centigrade to a bit over 90 every time I pushed it above 3000 rpm (I normally cruise her at 2800 - 2900 rpm), then falling back to 85 degrees when I eased her back to 2900 rpm. Both the rise and fall of temperature happens instantly, which does not indicate a true change (which would be more gradual), but feels more like a thermostat or indicator malfunction. This year it has started happening quite some times even at 2800 rpm, staying there for maybe 5-10 minutes and then falling to 85 degrees without any action (again instantly), while other times it rises and falls instantly ("playing" between 85 and 92 degrees). Any suggestions?