Just took my boat out for the first trip of the year and noticed a cooling issue. It is an '06 Optimax 115, SN 1B498653, Model # 1115D73HY. When i started it I let it idle for a few minutes. Water temp was 55 , air temp was in the low 60's. Temp was steadily climbing up to around 130 when I started to drive away and the temp was dropping pretty immediately. I watched it go from 120-130 right down to 80 fairly quickly when i was running at around 4000 RPM. If i throttled back into idle or near idle the temp comes back up. Is this a pretty straightforward case of the thermostat being stuck open? Or should I be evaluating something else? Water pressure according to the smart craft gauge was around 5 at idle, 10+ at 4000 RPM.