Hello, I have a boat with twin 260 Straight inboards with closed cooling system. This engine warms up considerably slower than the other. Starboard engine over heats under load over 2500 rpms. I can idle around all day and it runs and cools fine. Water flow is good ( but seems a bit less than the port) New impeller, thermostat, thermostat housing, belt, Fresh waterpump. Trans cooler is clear, as is the heat exchanger. Water flow from intake is almost identical to the port motor( I measured it) infrared temps show 160 on pump, thermostat, risers are just warm, the heat exchanger and hoses are not too hot. The only part of motor that seems like it could be the culprit are the left manifold is showing like 190 ish. could it be the manifolds? I believe they are coolant cooled and the raw water only goes to risers and the heat exchanger? Also I am experiencing a oil or coolant slick from exhaust into water and a bit of white smoke at start up from this engine. Engine seems to run good. Idles fine, starts right up.