I recently bought a flatbottom with a 81' 35 horse Evinrude in running condition. I know the guy I bought it from and he said it had not been run in about a year. I ran some Seafoam through it and had it out on the lake 3 times everything went fine. This last time I went I noticed a small amount of steam coming out of the exhaust port along with the water. The tell tale was flowing and warm to the touch but not hot. The lake is a power plant lake and water temp on that morning was 94 degrees. I decided to head back in and go back to the house. Once there I ran it in a barrel of water and checked the exhaust water temp with a thermometer. Water temp was 120 degrees and no sign of any steam. I could hold my hand on the cylinder heads for 3 or 4 seconds before it was to hot to touch. Pulled the plugs and check compression and the top is 143 psi and the bottom is 140 psi. The impeller was changed about 2 years ago but the motor went about a year without running.
you can drop your lower unit and attach a hose to the water tube and let it rip. If you take the hose off of the telltale where it goes through the cowling and let it hang free it will have a better flow. The little nipple it runs through restricts it when you are trying to flush something out.