Outboard jet over heating on idle?

[MSRiverdog]

I have a 2004 Merc 3Cyl 50HP I put a jet pump on a few years ago, it will over heat idling but if I bring it up to about 1000 RPM does fine. Any thoughts, I did put in a new impeller and checked the installation on the pump. Not a big deal except at the ramp.

 

[RiverBottomOutdoors]

Check thermostat.

 

[MSRiverdog]

Check thermostat.

Not that expensive to replace, may as well change it out at the same time, wouldn't pull it without replacing the gaskets. 143 or 120 degree, I'm in CT.