I have a 2001 Baja 272 with a single mercruiser 502. If memory serves me correct, the engine ran aroun 160 degrees water temp all of last year. I changed the impellar last fall just before winterizing the boat. Now, after summerizing the boat, the water temp is between 175 and 180 degrees. Can anyone tell me if this is normal and acceptable running temperature or do I have a potential problem on my hands.

160 is the proper temp. I would check it out right
away,do you have a water pressure gauge? Is the
pressure o/k, maybe the thermostat is sticking
or there is a restriction somewhere from the pickup
foward. Ck the oil cooler & make sure there are no
pieces of the pump stuck in there. Did you lube
the impeller on installation, It will burn right up
if you didn't. Good luck . Rick

My 502 will run at 160, but when you are running it goes up to about 170-180 during hard runs.

Thank you for the words of wisdom. I phoned Mercruiser and they are saying that the water temp should be anywhere between 175 and 190. However, I agree that I should be around 160-165 while running at 4500 to 4800 rpm. If I am not mistaken, I have a 160 dergree T-Stat as well.
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Mine runs at 130,but mine are carbed.

160 is simply when the thermostat starts to open. Ambient temp; boat load; etc. factors in. But 160 should be about right idling thru the no-wake and 175 is in zone for on plane operation. But right now with water temps being very cool, it should be running cooler than say, late July. Immediately upon coming off throttle the temp will spike temporarily due to sudden loss of coolant water pressure after working hard.

Did you add any kind kind of lube when installing the new impeller? If yes then this could be causing a little loss of suction until it wears off. Otherwise you may have some scoring inside the housing, and it doesn't take much, which will also cause loss of suction especially under loads.