Over heat on Yamaha

I have an Yamaha OX66 200 hp. The over heat alarm comes on when I idle for an extended time. It does not happen when I am running at higher rpm's for extended times. I recently had the impeller replaced but it still happens. Any ideas on what could be causing it ?

check the poppet valve see if its stuck or has a weak spring.

Change the poppit valve and the thermostat

The damper seal (Rubber Gasket) between the exhaust outlet and the water impeller section causes this issues as well. This should have been changed when the impeller was changed, but not always done by most.
If the poppet valve is free then this is the issue.

Ok, thanks for the replies.

Make sure it's peeing water at idle. My last one was a 2001 225 ox66 and it would sometimes clog up with mud and would take a little bit to get it cleared out when that happened.

Had the same thing happen. Replaced the impeller, no change. Replaced impeller, housing, plate, gaskets, etc. Once all was new, water pressure came back to 5psi at idle and 25psi at WOT. Could be the poppet like suggested, but for me it was a complete redo of the impeller set-up to do the trick.