High Temp. Alarm

[JCJ]

1999 200 Optimax (Ser. #0G886121) -

Been fishing an area that requires extensive idling due to high water. Noticed that when I'm idling for more than say 15 - 20 minutes, I'll get a continuous alarm followed by the high temp light coming on. I can shut the motor off and turn it back on, and the alarm will go away for about 1 minute before returning. No issues when getting on plane and running. The water pump was replaced less than 6 months ago, and my water pressure when idling is around 2.5 psi (WOT is 21 psi). The pee stream appears strong.

I cleaned the strainer, and back flushed the system, but that didn't resolve. I haven't checked the thermostats yet. They were replaced about 3 years ago, so not real old. One thing I noticed though, is that when I was running the motor on the muffs, my #1 and #3 cylinders were running about 20 - 25 degrees hotter than the others. I bought an IR gun from Harbor Freight, so know it's not perfectly accurate, but those cylinders were reading a consistent 170 - 185 degrees, while the others were in the 130 - 160 range. This temp reading was taken on the cylinder block, just behind where each spark plug is threaded in. Any ideas on what I may have going on? I'm really wondering if it's had this problem for a while, and I've never noticed it since I'm usually not idling for this amount of time???

Thanks in advance for the suggestions, ya'll. Appreciate it.

[Bob G.]

Since you have the IR temp gun, check the thermostat housings as it’s warming up. Should be able to tell if they are cycling.

[EuropeanAM]

ALWAYS start AT THE SOURCE: The Water Pump. Could be something as simple as a split gasket, bad seal, gear lube leaking into pump, or even one vane folded the wrong way for some reason.

[JCJ]

Appreciate it. I'll double check the pump and see if I see anything out of whack. I did see the thermostats cycle, so believe they're ok. Any ideas on why the #1 and #3 cylinders would be running hotter than the others? Do those typically run hotter for some reason?

[EuropeanAM]

That would be because there is no accurate measurement location (externally) on the cylinder head from which to achieve a consistently accurate temp.

Center of the thermostat cover is the "spot". Anywhere else (external) is subject to very erratic readings.