overheating question for a 79 mecrusier 470

[kjohn2007]

I have a 1979 Mercruiser 470 that is warming up too much past normal spot on the temperature gauge it's supposed to be 160 but it goes up to around 180 then when I put it in gear and goes back down some. I'm pretty sure its the thermostat not working properly. Anyone have any other suggestions what it might be?

 

[Bt Doctur]

impeller, riser/res, collapsed water inlet hose, growth at the inlet holes,