Impeller ?
 

Just got through de-winterizing boat (I know first of June, but it won't stop raining here in S. Oregon) hooked up fake-a-lake like I have for years. The way I do it is barely turn water on, and when boat starts turn it all the way on. Started boat, went over to turn water up, checked out exhaust and there was just a mist coming out, looked under boat at intake and fake-a-lake was not tight to hull, as I jump up to turn key off started to squeel then turned off. Total time for all this about 30 seconds. Hooked fake-a-lake tight to boat used same procedure as always started up water coming out exhaust like it should. Brought it up to temperature right at 175f totally quiet at impeller housing. Should I have any concerns that I did premature damage to impeller (just put new one in). Don't want to have problems on the lake, it's a Mercruiser and it's kind of a pain on dry land.

Also forgot to say, right exhaust manifold is fairly hot and water coming out of same side is pretty warm, whereas left side is very cool, never noticed before, is this something to be concerned with?