I've got a 31' Wellcraft with twin MerCruiser FWC 7.4 340's. The port motor stays at 145-150 all the time. The starboard motor runs 150-160 at 1800 RPM, but at idle it gets up to 175. At 3000+ it steadily gets hotter and hotter (up to 190) before I slowed down to 1800. Then it came back to 160 again. The impeller is new on that side. Any ideas?