Carbon Build-up in the Water Jacket

[Hasaler]

It's been a long time since I worked on engines and this is the first time I've worked on a marine engine.

I have a '73 Catalina 27 with an Atomic 4 engine. I've owned the boat for about two years. I think the engine has always run a little cold. I'm able to touch the engine and it never seem to warm up. I figured the engine just ran cold until the new problem.

I was recently doing some routine maintenance on the engine (oil change, fuel filter change, spark plugs) and I noticed that the belt was loose. As I was tightening it, the alternator adjustment arm came off from the water jacket side plate. The bolt that was holding it was stripped. I was going to re-tap it, but had trouble getting access. I ordered two of the water jacket side plate repair kits from Moyer Marine (I should have order all four). I took off the side plate and there was a thick black crust inside the water jacket. It also feels like there is debris from the build-up inside the water jacket. The build-up is probably about a 1/4" thick. At first I thought it might be a black iron oxide but realized it was probably carbon. Besides the fact that I can't mount the stainless steel bars without doing some cleaning, there is obviously a problem that needs to be corrected.

What is causing this? Is there a way to take care of this without overhauling the engine?

Thanks for the advice,
Steve

[Dana Paterson]

When I replaced my thermostat housing; I looked down into the water jacket and noticed a thin (<.5mm) coating of gritty black stuff. It feels kind of greasy. I just figured that's what cooked seawater looks like or maybe there was a blown head gasket in the engine's past. My engine temp is satisfactory. I'm curious, though.