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

On 4 Aug 2003 10:39:06 -0700, (Coff) wrote:


Questions:

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

Sucked up something that blocked the intake, like the plastic bag,
which fell away when you shut it down. Go find out why the big
honking warning horn either isn't working or isn't installed! You
should have got a big BEEEEEEEEEEEEEEEEEEEEEEEEEEP before that guage
got that high! If there isn't one....INSTALL IT!

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

Compression test on all cylinders. Watch cylinder banks for signs of
leakage outside, in the oil and in the closed circuit cooling if you
got it....indicating warped heads.

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

Got a good mechanic? Let him look it over.

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

Hmm....don't see how. I like the temporary blockage theory much
better. When impellers fail, they fail hard and for good.

You COULD have had a stuck thermostat. I'd change it anyways after
it's been to 260F!.....wow!



Larry W4CSC

"No, NO, Mr Spock! I said beam me down a WRENCH,
not a WENCH! KIRK OUT!"

On 4 Aug 2003 10:39:06 -0700, (Coff) wrote:

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?

Probable. Unless the thermostat "stuck", overheats don't just go
away". (BTW- the thermostat in my van stuck last week. Buried the
engine temp and oil pressure gauges.)

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

You can check compression, and compare oil pressure now with oil
pressure before. That's about it, unless you want to tear the engine
down. An oil change is in order, and I'd change the thermostat.

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

See #2.

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

Yes, and no. A bit of seaweed or other "munge" could temporarily
block the intake, or foul the impellor, and then be chewed up and
passed through the block. See #2 to protect your investment, don't
count on a "happenstance".

Thanks to all for any input you can offer!

Coff

Good luck.
noah

Courtesy of Lee Yeaton,
See the boats of rec.boats
www.TheBayGuide.com/rec.boats