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