Motor getting hot

I have a 1984, 15 H.P. Yamaha that runs well. But this past week while I fishing I noticed that the back of the motor, just below the head, got extremly hot. I couldn't keep my hand their longer than 20 seconds. The out spout had water coming out of it, and the lower unit and head was not hot. Is this normal? Should I replace the impeller? Average cost for the shop to replace the impeller?

I just picked up the motor this spring, so I don't know the history of it. But it starts right up, and is a strong motor.

Thoughts?

Sounds normal to me, explosions going on in those cylinders, its gonna get hot. As long as the pee hole keeps flowing is a positive.
Tim

Yes put an impeller in it. Also look at the cup and lower wear plate. IF there's a groove in either one, the water volume can be decreased, which causes them to run warm.

It might be peeing but is it peeing HARD? Yamaha's pee real hard. Not just a dribble like most of the others (Mercs are notorious).

If you find that the impeller has come apart, make sure to clean out the water tube (back flush with air). Once the new impeller is in, I'll sometimes pull the thermostat and start the engine...if there's anything in the powerhead, it'll usually come out of the thermostat hole.

For peace of mind, I'm taking it in next week.