We had the same problem a couple years ago, it was the elbow. Many "Experts" told me not to waste time with the elbow on a freshwater boat. Wrong.
Duly following the "expert" advice I fixed / replaced everything else and reamed all the tubes in the heat exchanger using wood dowels. It was not an entirely bad exercise as some tubes were in fact clogged, the pump bearings and "cam" were iffy (The cam is not a replaceable item), and the belt as well as all the rubber hoses had seen better days. But in the end elbow was completely sealed shut by deposits. I did a lot of research on this here's the bottom line: - If your elbow is rusted in place / un-removable from the riser: Remove and replace the riser too. The riser is easy to remove / I got a brand new one almost free as they are a common take-off item these days - Elbows self-destruct in freshwater the same as saltwater. The deposits are the real problem. Much like seawater, lake water is a soup loaded with stuff in suspension that gets separated from the water because of the heat and steam / the very shape of the elbow and gravity does the rest. No matter what metal it's made out of. -From all the research I've done stainless elbows get stuffed-up at the same rate as cast iron units and the corrosion resistance is pretty much immaterial as they clog-up / need to be replaced as well. - If the elbow would have been replaced sooner, my hoses would not have been exposed to high pressure which caused leaks and their ultimate somewhat premature demise. I think the same could be said about my pump. I was eating through impellers like they were dirty underwear because it had to work that much harder to push water through a partially obstructed elbow. The cam wear is probably related to that as well (Not 100% sure on that) - Checking the elbow yearly or every 2 years is a great idea. - Once you get the hang of it, they're pretty easy to remove / replace, even in my extremely cramped engine compartment. My 2 cents. Good luck on the project. -Francois Rivard 1990 34+ "Take Five" Lake Lanier, GA
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