Friday my son & I took our boat out for a while. After several
minutes, I had him take the helm & I went below to change. I was down
below for several minutes, and heard the RPMs start to slow. Thinking
he might have bumped the throttle, I glanced through the forward hatch
up at the fly bridge, and he seemed to be okay. I again hear the
engine start to slow, and went above to see what was happening. The
boat was falling off plane, and the RPMs were at about 2900, where
they are usually at about 3400. As I reached for the throttle, I
glanced at the temp guage, which was buried at 260+. I immediately
moved to shut the engine down, but it slowed & died on its own.

Lifting the hatch, the 5.7 Merc was HOT. I turned the key only to see
if it would turn, which it did. Later that day, I ran into my
mechanic in the evening at the boat club. He looked at the oil, &
there was no water contamination. He had me start the engine, & it
sounds and ran fine. He could tell the impeller was working & the
temp was normal.

Saturday, I started the engine & ran it for about 20 minutes in the
slip. It ran fine and the temp guage was right where it should be.

Questions:

1. Any idea on the cause? Did we pick up a plastic bag or such?

2. What can I do to verify the engine didn't receive any permanent
damage?

3. Any tests I (we) can run to insure the engine's integrity?

4. Can an impeller just quit working & then start again?

Thanks to all for any input you can offer!

Coff