Got time to investigate the root cause of the starboard engine overheating today. Put it off for a week but it had been running hot on the way back from Sylvan last weekend. The engine only ran hot at higher speeds so I had a feeling it was something blocking a coolant line or an impeller that was starting to fail.
After a few hours of taking things apart I found a pretty large blockage in the thermostat housing at the top of the engine.
Taking the water pump off didn’t show any damage so I believe this must have been left over from an impeller failure a few years ago and come loose from where it had been lodged and got caught in this spot.
Impeller fins all checked out OK.
Had enough boat project for one day and came home for dinner. Still digging the last few stubborn bits out of the housing…
Day 2
Fished the last piece out of the housing and returned to the boat to reassemble everything. It went pretty smooth:
Started both engines and let them run for a bit, tighten a hose clamp or two but still had a leak where the thermostat manifold mated with the engine – which wasn’t a huge surprise since I re-used the gasket. New gasket on order: https://www.amazon.com/gp/product/B09H2N6NRY/ref=ewc_pr_img_1?smid=A355RQQR8E2O1&psc=1. Getting the entire assembly was cheaper from Amazon that getting this part: https://www.mercruiserparts.com/530451-gasket ($5.50) and paying for the standard shipping fee of $22 🙁
Turned the idle down on the port motor while I was in there. It was dieseling the last few times I shut it off. After some reading on the internet lowering the idle was the easiest possible fix, and it was ~100 RPMs higher than the starboard side.
