1988 Merc 5.0 I/O running hot

[Jim Harpold]

Hi, I have a 1988 Winner with a 5.0 Merc I/O with under 100 hours. I purchased it to fish Lake Michigan. The motor runs great and trolls at low 2.3 mph. Today when I took out for the first time since buying I noticed that the temp got hot while trolling 240 degrees. I turned the motor off to pull my fishing gear then restarted the engine the temp had dropped about 20 degrees. I started for the harbor and was running about 3200 rpm within 100 yard the temp dropped to 120 degrees. Any idea on my problems as I really want to be able to troll this boat and don't want to buy a kicker

 

[cr2k]

Re: 1988 Merc 5.0 I/O running hot

First guess is the sea water impeller. These are a replace every other year maintenance item and the first thing you do to a new to you boat before you even take it out. The impeller is rubber so if it is used it wears, if it is not used it sits bent and gets a set in the blades (they get hard) and doesn't pump well.

If you ever start it with out muffs and water you will fry the impeller in 15 seconds or less. Also any impeller pieces missing MUST be found as they will restrict water flow somewhere in the system and cause overheating.