OK, I am a new boat owner and am learning the hard way. I am pretty
sure that I have fried the water impeller in the stern drive. I have
an '81 Glastron SX-190 with a Mercruiser 228hp 305. I didn't know,
until now, that the boat should never be started even for a few
seconds without water supply at the stern drive. Well sure enough, I
got the boat out to the lake for the first time this year and I have
an overheating problem. I took out the thermostat at the lake
thinking that maybe it was the culprit. Still the boat overheats at
idle. When I rev the engine to about 2000 rpm, it cools back down.
The only thing I can think is that the impeller is not working at idle
speed and barely working enough when I get it up to 2000 rpm. Does
this sound like the impeller is working poorly or could it be that I
need to put in a new working thermostat? The stat that I took out was
140 degrees. Is this too cool or the right one for this engine? Any
info would be appreciated. I am good with cars but am learning
quickly that not everything I know is true anymore (i.e. cranking the
engine and running it without coolant for 5 seconds is NOT acceptable
like it would be with a car). Any other things I should be aware of
would be appreciated. Also, there appears to be quite a bit of
voltage loss in the 23 year old wiring. I am thinking about rewiring
the boat. Any advise or horror stories?

Chris

Almost surely you have a bad impeller. Even though I have long known not to
run it dry (a friend did that to a 188 Mercruiser in the 1970's), I was having
the same symtpoms: Overheat at low speed, cools down at speeds over about 1500
RPM. Shop replaced the impeller, and no problems since.

I suggest that you contact the local Power Squadron . . . not meaning to be
snide about it, but the water is full of people who "think" they know
everything . . . and don't.

I've been affiliated with the Power Squadron her for 29 years . . . and I learn
new stuff all the time. Don't be afraid to learn!

Almost surely you have a bad impeller. Even though I have long known not to
run it dry (a friend did that to a 188 Mercruiser in the 1970's), I was having
the same symtpoms: Overheat at low speed, cools down at speeds over about 1500
RPM. Shop replaced the impeller, and no problems since.

I suggest that you contact the local Power Squadron . . . not meaning to be
snide about it, but the water is full of people who "think" they know
everything . . . and don't.

I've been affiliated with the Power Squadron her for 29 years . . . and I learn
new stuff all the time. Don't be afraid to learn!

Second thought:

Re-wiring the boat. Modern boats are wired with "tinned" marine grade wire, at
least the good ones, and the ones intended for salt water.

Ask an expert about how to do it, even if you're competent to do the "grunt"
work yourself.

Second thought:

Re-wiring the boat. Modern boats are wired with "tinned" marine grade wire, at
least the good ones, and the ones intended for salt water.

Ask an expert about how to do it, even if you're competent to do the "grunt"
work yourself.

"Chris" wrote in message
om...
snipped bit was here The stat that I took out was
140 degrees. Is this too cool or the right one for this engine?

I believe that is the right temp for the thermostat. At higher temperatures
the calcium will precipitate out of the cooling water and form scale in your
cooling passages, eventually blocking them. It doesn't happen in cars
because you have a limited amount of calcium available in the coolant (it
does happen actually but the amount available to precipitate out is limited
to what's available in the coolant). In a boat motor that has a whole
lake's worth (or ocean) to draw form it can add up.
--
Ken Heaton & Anne Tobin
Cape Breton Island, Canada
kenheaton AT ess wye dee DOT eastlink DOT ca

"Chris" wrote in message
om...
snipped bit was here The stat that I took out was
140 degrees. Is this too cool or the right one for this engine?

I believe that is the right temp for the thermostat. At higher temperatures
the calcium will precipitate out of the cooling water and form scale in your
cooling passages, eventually blocking them. It doesn't happen in cars
because you have a limited amount of calcium available in the coolant (it
does happen actually but the amount available to precipitate out is limited
to what's available in the coolant). In a boat motor that has a whole
lake's worth (or ocean) to draw form it can add up.
--
Ken Heaton & Anne Tobin
Cape Breton Island, Canada
kenheaton AT ess wye dee DOT eastlink DOT ca

Just fixed a problem with the same symptoms. Drove me nuts when replacing
impellers didn't help. Then I found a kinked hose while getting ready to do
a backflush. Prolly is a fried impeller but if that don't fix it look at
hoses.

"Chris" wrote in message
om...
OK, I am a new boat owner and am learning the hard way. I am pretty
sure that I have fried the water impeller in the stern drive. ....
..... When I rev the engine to about 2000 rpm, it cools back down. ....

Just fixed a problem with the same symptoms. Drove me nuts when replacing
impellers didn't help. Then I found a kinked hose while getting ready to do
a backflush. Prolly is a fried impeller but if that don't fix it look at
hoses.

"Chris" wrote in message
om...
OK, I am a new boat owner and am learning the hard way. I am pretty
sure that I have fried the water impeller in the stern drive. ....
..... When I rev the engine to about 2000 rpm, it cools back down. ....

"Chris" wrote in message
om...
OK, I am a new boat owner and am learning the hard way. I am pretty
sure that I have fried the water impeller in the stern drive. I have
an '81 Glastron SX-190 with a Mercruiser 228hp 305. I didn't know,
until now, that the boat should never be started even for a few
seconds without water supply at the stern drive.

Yep, true, never ever run the engine without a flow of water!

Of course, this is a "do as I say, not as I do" thing. I always hit the
starter before I get to the ramp just to make sure that the boat will start
when I get it to the water. Crank, Start, shut off! Not a good idea, but I
do it anyway. I get three or four years out on a water pump impeller.

Your boat is an '81. Any idea when the impeller was changed last? How many
hours it has on it?

It was possible, indeed likely that the impeller was on its last legs when
you bought the boat. There are two approaches to changing your impeller:
one is wait until it fails, the other is preventative.

On my ski boat, I can change the impeller with only a screw driver in about
10 minutes with the boat in the water. I carry a spare impeller at all
times, just in case (I have also sucked up weeds that chocked off the water
supply and caused the impeller to burn out). For me, running it until it
fails is not a big deal.

Not sure about Mercruisers, but some I/Os and all outboards the water pump
is in the lower unit. You don't want to be changing the impeller with the
boat in the water. Having the impeller fail can ruin your day, weekend or
even life if you happen to be off shore when the water pump fails and you
can't fix it. In such a case, changing the water pump impeller every year
or two is a good idea.

Rod