Bad move on my part. Powering out of my 18" deep mooring at dead low yesterday, prop almost out of the water and chruning through black muck I got an engine overheat alarm. I shut down, waited 10 minutes, poled out to the channel and caught a few schoolies while I waited.
10minutes later I cleared the water intakes of the muck; submerged the prop fully and started up. No alarm.
I didled out of the pond at ~ 1000 RPM's; when I got out of the pond and opened up the engine it was not right; it sounded like it was not burning fuel correctly; it would not go above about 2500 RPM's without a scary vibration. Lots of smoke also from unburned gas.
Shut down once more; wait 10 more minutes and start up in neutral. This time I revved the engine in neutral up to 4000 RPM's for 30 seconds or so; it sounded fine. Dropping back to idle I brought it up slowly to 2000, then 3000 RPM's and found it running normally. I ran gingerly that morning staying below 4000 RPM's and powering up more gradually than I usually do.
I talked to the dealer today who suggests I got sand or muck in the impeller of the water pump or in the thermostat. He suggests replacing both to be safe even though they were both replaced last fall and are brand new. he also suggests to see whats going on:
run the engine at idle 10 minutes to get it hot
take the cowling off and feel the block - if cold I have a problem; if on
fire I have a problem, if hot to the touch, but not burning, I'm OK
he also says if I run carefully, 3-4000 RPM's even if the thermostat is bad, that I'll be OK for a week or so.
The engine is a Yamaha 130 Saltwater series.
Any knowledge or wisdom is appreciated.