I have a 1988 mercuriser 5.7 (carb) Alpha 1 equipeed boat and it
recently started running a little hot - not overheating but hotter than
normal. It normally runs at an indicated 130 degrees or so under any
conditions - idle, cruise, wide open, summer and winter. The other day
it started climbing up to 180-ish at low rpm's and went down to 150-ish
at cruise (3000 rpm). It ran at a steady temp for a while and then I
decided to try wide-open. The temperature started climbing pretty
quickly so I brought it back down. The temp came back down to less than
160 and stayed. This happened all of the sudden with no known causes.
The pump in the outdrive was replace in May (annual maintenence), the
recirculatiing pump on the front of the engine was replaced 2 years
ago. The manifolds have not been replaced since I bought the boat in
November of 2001. I'm in salt water (Chesapeake Bay) BTW. Oh I
forgot, I took out the thermostat and it seems to be working properly.
Both it and the temperature sender were replaced at the same time as the
circulating pump. So, what's up? Is it a clinker?

JohnH wrote:

On Tue, 13 Jul 2004 23:24:33 -0400, mike hicks wrote:
[snip]

Mike, I have the same engine in a 1997, also in the Bay. If this were
mine, I'd replace the thermostat first, and then see what happens. Have
the manifolds and risers *ever* been replaced?

My normal operating temp is about 160. It gets there and stays there.

Hopefully, some of the mechanic types will provide a little more, and
better, information.

John H

On the 'Poco Loco' out of Deale, MD,
on the beautiful Chesapeake Bay!

Greetings:

On my friend's boat there were a couple of hoses that (IIRC) came
out of the thermostat housing to the front of the heat exchangers. Inside
these two hoses (one on either side) was a small check ball mounted on a
brass rod with a spring on it that passed through the thermostat housing so
that there is one ball on each side. They have a nasty habit of getting
mineral deposit buildup and sticking (closed) to the thermostat housing. If
you have these try cleaning them up real good. Good luck!

-Jason

Jason Bourne wrote:

JohnH wrote:



On Tue, 13 Jul 2004 23:24:33 -0400, mike hicks wrote:


[snip]


Mike, I have the same engine in a 1997, also in the Bay. If this were
mine, I'd replace the thermostat first, and then see what happens. Have
the manifolds and risers *ever* been replaced?

My normal operating temp is about 160. It gets there and stays there.

Hopefully, some of the mechanic types will provide a little more, and
better, information.

John H

On the 'Poco Loco' out of Deale, MD,
on the beautiful Chesapeake Bay!



Greetings:

On my friend's boat there were a couple of hoses that (IIRC) came
out of the thermostat housing to the front of the heat exchangers. Inside
these two hoses (one on either side) was a small check ball mounted on a
brass rod with a spring on it that passed through the thermostat housing so
that there is one ball on each side. They have a nasty habit of getting
mineral deposit buildup and sticking (closed) to the thermostat housing. If
you have these try cleaning them up real good. Good luck!

-Jason


Thanks for the reply. I pulled the housing off and it looks like it's
not long for this world. There is lots of corrosion. The area with the
balls was particularly bad plus lots of gunk in the springs. I've
cleaned it up (probably replace it this winter) but I haven't put it
back on yet. I'm replacing the thermostat even though I think it's OK..

mike