1989 70 hp Evinrude Troubles

Hello. new to this board, I have a 1989 70hp Evinrude that has been driving myself and the prior owner crazy. It's on a 24ft Lowe Pontoon, that I purchased from a friend, here is what it does. We can run the toon all day long at 2000rpm and lower, take it up to full power and after a few minutes it will cut back and chug. Again it will continue to operate at 2000 rpm. It has had 2 power pack changes, 2 temp sensors been run on 2 differant dyno's and on the dyno's it never acts up. Take it back to the water and problem reappears. I have used the toon this summer and up until last weekend never acted up but now it's back. The water temp is much warmer and two other items I noticed, Volt gauge is running +14--16 volt when it acts up other times it's right on 12v. Also the temp gauge is way low and then we start a full throttle run and up comes the temp to about the center of the gauge and then it's starts to cut out and temp drops off. Toon does sit low in the water in the back and so raised the motor 1 hole, thinking that the exhaust was getting covered..no cure. Water pump was NOT been replaced but motor is very warm to touch. Any HELP would be great!

Re: 1989 70 hp Evinrude Troubles

Sounds to me like overheating.

Giver her an impeller and clean out all cooling passages. Maybe a news thermostat, too.

Re: 1989 70 hp Evinrude Troubles

Your motor head jacket temp. will rise to about 140-145 degrees. That's normal. If it's much higher than that you have a problem. I have not used them but there is a wax type stick you can buy and put it on on the cylinder and if it melts it's too hot and it's probably time for a new water pump. I have a 1987 90 and when I rebuilt it I also noticed calcium type build up in the water jacket cooling compartment which would have restricted water flow. Try to determine the actual temp your are running at. I just added a temp sender to mine just for peace of mind, $35.