Melandre wrote:
This is not a closed cooling system just a standard cooling system
where the boat draws sal****er from the ocean. The manual says that
the thermostat should start opening at a temp of 160F and be fully
opened at around 180F.


If I read that last sentence literally, it is simply describing the
operation of the thermostat and not the recommeded operating temp for
the engine. There is no reason the engine coolant temp could not or
should not rise above the temperature at which the thermostat is fully
opened.

I'd be surprised to discover that you truly have raw water cooling. Are
you sure you don't have two coolant circuits on your engine? One
comprised of
fresh water and antifreeze that circulates through the block and heads
(after the thrermostat opens of course) and the other the raw water
flow that is pumped through your heat exchanger to extract the heat
from the engine coolant (and often through the exhaust manifoolds or
risers) before carrying the extracted heat out through the exhaust
hose?

However, as you are operating in salt water, it is better to keep the
engine coolant temp down to about 190 or less. At about 190 degrees,
the suspended salts begin separating from seawater and will begin
building up
in your cooling circuit. Not a good thing.




I plan to remove the thermostat housing (and the new thermostat) and
reassemble the housing without a thermostat in it. This should allow
me to determine if the problem is the thermostat or not. Without a
thermostat, I am assuming that cooling water is drawn all the time so
in therory, the boat should not overheat. If it does, it probably
means that the problem is elsewhere (plugged hose, riser, water pump,
impeller, etc..)

A.

On 17 Aug 2005 21:26:53 -0700, wrote:


Melandre wrote:
I am suspecting my boat's (1990 Ford OMC Cobra 2.3L) overheating
problem comes from a defective thermostat. Today, I replaced the
thermostat but the gasket that I was given does not fit the housing at
all so I had to reuse the old worn gasket for now. I started the
boat and it gradually went to over 200 degrees which means the problem
is not fixed. I also noticed that steam was coming out of the
thermostat housing around the old gasket. So obviously I don't have a
100% seal and I will need to find the proper gasket.

However, I am wondering if the leaking gasket would be enough to
cause the new thermostat not to work or if I simply misdiagnosed the
problem in the first place and will have to look somewhere else?

Impeller and water pump was replaced 2 months ago so I don't think
this is the cause. Will have to also check the hoses and the water
intake I suppose.

Andre

It may be OK for a pressurized cooling system to run at 200 degrees.
What does your OM say? However, if you have steam leaking out from
around the thermostat gasket you don't have proper pressurization and
that will lower the boiling point of your coolant substantially.

No, it is (unfortunately) just a standard cooling system (it is only
17.5' boat). Simply put, recently the boat starts hot (needle creeps
to the 200F to 250F range) and after a random period of time (averaging
1 to 4 minutes) needle suddenly drops to around 150F and all is well
and engine appears to stay at approx. 150F.

If it was the impeller or clogged hoses, wouldn't the problem continues
after 3-4 minutes of running? Andre

Melandre wrote:
No, it is (unfortunately) just a standard cooling system (it is only
17.5' boat). Simply put, recently the boat starts hot (needle creeps
to the 200F to 250F range) and after a random period of time (averaging
1 to 4 minutes) needle suddenly drops to around 150F and all is well
and engine appears to stay at approx. 150F.

If it was the impeller or clogged hoses, wouldn't the problem continues
after 3-4 minutes of running? Andre

If you are dropping back to 150 degrees after an initial heat up to
200-250 degrees, it does indeed sound like the thermostat. Impellers,
hoses, obstructions, etc are permanent situations, not self correcting.

If you test the thermostat in a pan of water, (using a candy
thermometer to note the temperature at which it is opening), and it
appears to be opening within specs you might need to go to a thermostat
with a lower rating. There's no good reason to heat up to 250 degrees
if your engine is happily running at 150.