I have a mercruiser 1997 5.7 liter I/O set-up; I have been using it since 1997.
Early this spring after haul-out I noticed that the starboard manifold and riser were running much hotter than the port. However the engine operates at normal operating temps and doesn't overheat. The marina replaced the thermostat which was cracked and needed replacing. The problem did not go away. I took it back and asked them to examine the risers etc.; when they took the risers apart they were badly coroded after 5 yrs of use- they suggested replacement and I agreed. After replacing the risers ,manifold and elbows the problem still persists. I would say that the temperature differential between starboard(hotter) and port (cooler) manifold and risers is at least 30 deg. I don't know if this is even a problem. But it doesn't seem right. After prolonged operating (or even after a short operating period) the port riser is warm, but it is cool enough so that I can keep my hand on it indefinately- the starboard riser gets so hot that I can barely touch it for a second. But engine temps are normal. Any suggestions would be greatly appreciated.