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Mercruiser 454 MPI Overheating - Problem Solved!


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My engine was overheating at WOT.

Then it would start running warm while just running hard.

Installed new thermostat, new impeller, and backflushed the system.

Still doing it.

Installed new manifolds & riser. The old ones didn't look bad enough to be causing the problem.

While the engine was accessible, decided to replace all the hoses as a precaution.

Problem # 1 was found, the honeycomb engine oiler cooler was partially clogged even after backflushing the system. I took it off & used a straight piece of wire to poke out all the organic debris.

Problem # 2 was found by the mechanic, the fresh water hose coming from the outdrive was crushed by salt build up and restricting flow!

Problem # 1 didn't cost anything to fix. Problem # 2 cost a bit, but still a heck of alot more then overheating the engine.

Just a few things to look for outside the ordinary.

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Hm, I just went through absolute heck replacing that line through the transom. Original variation has no support where it goes through the gimbal housing, and the update kit replaces it with a hard plastic tube. I had heard the update was due to corrosion crushing the hose, guess they were right!

Must feel good solving that problem. Happy boating!

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