Merc 170 very, very hot to the touch but temp guage normal

[stuffer]

Just tuned up my 1985 Sea Ray Seville Cuddy with the Merc 170. Went out to the lake and while it was running rough at first, we did get it to smooth out somewhat and ran it at 25 to 30 mph for about 20 minutes. The engine rocker arm cover was so hot that I could only touch it for a split second. The temp guage ran normal all morning (170 degrees) Even the spark arrestor was so hot I couldn't touch it. Rebuilt the lower unit pump last year. It should be working fine. Got plenty of coolent in the resovior. Oil presure is normal, just above 40 after engine got warm.

What could be causing this. I can remember being able to touch the cover and it was only warm.:smt013