5.7l omc cobra overheating at low idle

[hays4]

Help: my 1988 IMP ELenganza 5.7l omc cobra is overheating at low idle. I have replaced the water pump, even removed the thermostat. I have good water flow. Boat will not overheat on watermuffs, but when I run it on the lake, it heats up at low idle. As soon as I open it up, it cools back down to 120 - 130 °.
What else can I check?
Thanks again fellow boaters.

Brian

[indybleck]

Check some other threads about a small leak somewhere, or losing prime from your lower.