Hot water backing up to thru hull

[flycavalry]

Moter has been not started in years. Finally got started but only a trickle of water out exhaust. I checked impeller and t-stat, all ok. When I bump the starter I get a good initial flow but when it is running is slows to a trickle. While the temperature climbs the water line to the thru hull starts to get warm. Might my outlet from my exhaust manifold be clogged or maybe the exhaust itself be rusted up?

[Al Schober]

Coolant flow is a good thing. Don't run the engine without it, at least not long!
Some quick things to do are a) make sure the hull valve is open and clear (disconnect the inlet hose and open the valve), b) remove the thermostat (you can always put it back later), and c) check the outlet elbow on the manifold.
It's really just a step by step process. Hull valve, strainer (if you have one), pump, etc - until you find the piece that's restricting flow.

[Sam]

Lining of any rubberized [exhaust] hose may be coming loose with some heat. As an additional note, if engine has been sitting for years I would not put much faith in the long run in your impeller [probably not your current issue].