Temperature range for the M25-XPB engines is 170-190 so you're ok if that's what you have.. the change in behavior is something to look into.. have you changed the thermostat to be sure its not that?Last year, our first for the 310, my engine temp was rock solid at 170 until we hit high temps in the summer and would go as high as 180. This year so far it is sticking a bit under 180. I've checked the strainer and it is clean. Fresh water boat whole life, 670 hours, water pump up graded and all coolant lines changed out and fresh coolant. Should I care?