My 2002 Merc. 496 Mag has an issue with oil overheating after a long haul (1 hr + running) and dropping oil pressure. Water flow out of port side exhaust significantly less (40% less) then starboard. Riser and exiting water warmer on port side to the touch. Had a new manifold installed on port side (cast iorn starboard original cast aluminum )when winterized last season. Had marina look at this and they said I had a blockage (Seaweed /Grass) in power steering cooler which they replaced but still have less water flow issue. Overheating oil issue used to occur after 20 min now after 1 hr+. I was told they checked oil cooler and rest of system with no obstructions found. Raw water flows from power steering cooler to oil Cooler to heat exchanger on port side. Continuous alarm sounds till throttle brought back to neutral with significant oil pressure drop according to gauge. Engine temp will maintain 150 degrees. Where should I start looking to correct this problem? Raw water pump has new impeler that was the first thing i replaced. Could the newer cast iorn design have different water passages(smaller), causing diffrent flow and temps?

Did the problem start before or after the new mainfoild? It Sounds like to me some one that understandes how to read A hooked up scan tool with live data as it is happening will need to go for a ride in the boat to find this one. Also take a infa-red temp reading gun with you.

I need to find a good marina with a good mechanic in new jersey!!!!!!

Call this number and ask them who is the best EFI service shop in your area is. Mercruiser Consumer tech Support 405 743 6566