43 Merc Steam emanating from starbord side when flushing out

"Hi There
I have an 02 Mercr

"Hi There
I have an 02 Mercruiser 4.3TKS V6. The starboard riser appeared to be overheating (could only put your hand on it for 4-5sec before it was too hot to touch)after being ran for a few hours.Port side did not have much heat in it at all. The temp gauge was flucutating from 150-180F all day.Also, when flushing out, steam was coming from the rear of the boat on starboard side. I have remove risers/manifolds and water pump mounted on front of engine and all appear to be in good condition. Im not really sure what else to check for/where to chase the problem to from here.
Any ideas would be appreciated
Also, is 150-180F normal running temp. for this engine and is it normal for it to flucuate while running?
Thanks"

"has the impeller ever been ch

"has the impeller ever been changed ? if it was damaged at some point, there could be a blockage in the starboard riser. Temp will fluctuate depending on lake/pond/river/ocean water temp, engine load, condition of impeller, and a few other items..

I beleive 150-180F to be normal. but could be an idication if only recently has been fluctuating.

unless you remove the cover on the back of the engine circulation pump as aposed to the raw water pump, you wont know the actual condition of the vanes, which unless you run in Salt Water alot 'should' be in good condition for an 02, i would think.."