Engine exhaust and manifold overheat

74 Mercruiser 5.0 302 V8, How warm/hot should the water be leaving the exhaust through the prop with the hose connected? I have an older boat and I know the little things should be failing and not working properly like my engine temp gauge, manifolds, & risers...So one of the many questions I have are my engine temp says it is overheating but I can still put my hands on the manifolds and risers without getting burned (put hands on for 10 secs or so). Also my boat is stored in a shallow channel and I pulled the t-stat to clear up debris and let water flow easily, when doing this there were flakes of rust in the t-stat, leaves, and little nuts. So commonsense tells me thats not right. To unclog or clear this debris do I pull the manifolds/ risers and use a shop vac to suck everything out or disconnect a hose and flush it out? Please any help will do!

Re: Engine exhaust and manifold overheat

True; that's certainly not right.

A bit of rust is to be expected but where are the leaves and little nuts coming from? Was a hose left off at one time while on a trailer, to allow mice to make a nest?

I'd open all the coolant connections and flush with a hose, 2 directions alternately.
If you have lots of clear water flowing after the junk is out of there, should be ok.