LouC wrote:
Are your manifolds on the closed cooling circuit or are they also raw water cooled? If they are raw water they and the risers both could be starting to clog with rust. I checked mine last year and after 4.5 seasons in salt water on one side 1 of the 4 outlets was starting to clog. I had a new set and replaced em, but that was not really the cause of my running hot issue. What it turned out to be (not thermostat, not impeller) was barnacles growing in the water intakes, I had to remove the plastic screen in the lower unit to get them all out. After that it runs at its usual 165*.
The issue with salt water cooled manifolds and risers is not just overheating, but if the water passage corrodes through, or the gasket between the manifold and riser leaks, it can put salt water into a cylinder. Most here recommend changing between 5-7 years.
Thanks for the run-down. I've had a diver doing the bottom work monthly but I'll have him double-check the intake. The strainer was pretty clear, just a few stray bits of leafy material. I've seen much worse. I'm less inclined to think it was blockage because the temp would run up just as I put an actual load on the engine. At only 1k RPM as I was maneuvering out of the marina it started spiking. So it wasn't a matter of it only happening under cruising or WOT load.
I pulled out the thermostat and that solved the overheating problem. But the side effect is the engine won't come up to temperature, of course. So it's not like I can run it that way.
They're FWC manifolds and RWC elbows (no risers in-between). Here's the page from the Crusader manual:

I've picked up a new thermostat and will give that a try. I've also picked up a set of elbow gaskets. I suppose the only way to tell if the elbows have issues is to remove them, correct?
I also plan on taking my IR thermometer with me next time (which I probably should just leave on the boat). I'll use that to compare temp levels between the two engines. Presumably if I've got a blockage I'll be able to narrow down where based on the temp differences between the two engines (at the same places, of course). The troubleshooting steps for cooling mention reversing the flow as a means to dislodge potential blockages.
I popped open the inward side of the heat exchanger and it was totally clear. I'm guessing that was just the FWC side. Getting to the other side is a hassle as the decking above has to be removed (and the seating above that too). I suppose I could pop off the other side over on the port engine to have a peek. If that looks nasty then it'd be reasonable to assume the starboard side isn't any better. The factory manual says pull 'em and have them cleaned by a radiator shop. But I'm guessing since removing the thermostat eliminated the temp spike then the exchanger is flowing freely enough to do it's job.
I've replaced the heat exchanger anodes before, usually every other season. They've never been totally eaten away though, probably just half-way. I did them last spring and when checked yesterday they still looked practically new.
Hopefully I'll be able to get down there tomorrow early. So I'll be able to get an overnight order in for elbows (~$150 each) Shipping will be a killer, but that's less "expensive" than losing another boating weekend.