I have a fresh water cooled 350 in my 1987 Wellcraft StTropez. My proplem is on the port motor. I can idle all day long and not go over 160 degrees, when I take the boat out for a ride within 5 minutes the temp climbs to 180 to 185 and when I slow the boat down the temp climbs to 190 degrees and won't come down unless I rev the motor up to about 4000 rpm and then it drops down to about 170 degrees. Is this caused by raw water pump or my frew water pump? I'm leaning towad my fresh water pump seeing that the temp drops down at 4000 rpm. and it's not the belt just put a new one on and it's tight.