On Thursday, we dialed the speed up to 7 knots. This means a bit over 2,000 RPM on the tach.

And the temperature started to increase. And increase. I don't often check the temperature. But I did manage to notice it in time.

Did I mention we had guests?

We had guests. See Friends and Boats. First-timers on Red Ranger, too, so everything's mysterious and a little scary.

I pull the throttle back. I run below, calling out, "Nothing to worry about. Remain calm." As if that makes anyone feel calm.

There's no cooling water spraying around the engine room or bilge. (whew!) There's a lot of steam coming out the exhaust pipe. With the gauge over 200°F, Cooling water is boiling away. Which makes sense.

There were no alarms. Yet.

At low RPM's, the temp fell. At high RPM's it rose.

Possible cause 1. Blockage in the input — i.e., grass in the strainer.

Possible cause 2. Failing impeller in the raw water pump.

Remotely possible causes include broken or leaking hoses or jammed up heat exchangers.

Saturday, CA cleaned the strainer. She found grass. ✅

I took out the impeller. You can see a vane partially missing. ✅

I poured the water out of the oil cooler and didn't see any obvious rubbery parts. So. I'm guessing the busted up pieces flowed on through the system and out the exhaust.

Ran the engine at idle to pressure test it when I was done. Worked.

Now to run up the RPM's and race around at 7 knots again to see if it's fixed.