Gene wrote:
On 29 Oct 2006 15:59:53 -0800, "
wrote:

I believe the thermostat in my Mercury 115hp 4-stroke outboard is
broken. Now, I need info about which thermostat that I should use to
replace it.


Easy answer. Go to the boat dealership with your engine's model and
serial number. Based on that information, ask them for the correct
part. Tip: Never assume that the part you removed was the correct
part.

Yes, I asked the dealer, and according to the stock info system, mine
should use 120 degree thermostat.

As Larry noted, if the thermostat is in the condition you suggest,
your engine is probably toast. If it is not, then the thermostat must
be admitting at least some cooling water to the water jacket.... or
some information you have provided is faulty.

You are exactly right! I checked the old thermostat in a wrong way.
Actually, the old thermostat is not broken. I mistakened the axis of
the thermostat as the valve.

I decide to replace the old one anyway because the old one starts
opening the valve at 140 degree instead of 120 degree as what it is
rated (the new one starts opening right at 120-125 degree).

Thanks for pointing out that my test might be faulty. Otherwise, I may
not give it a second test.

Jay Chan