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.

OK, I will ask the dealer when I go there to buy a new thermostat.

I have a couple questions related to the old/dead thermostat:

1. What does "sticking termostat" mean, like when people say "the
sticking termostat is causing problem"? Does this mean the termostat
sticks at the "close" position and cannot open up like what my old
thermostat is?


A thermostat can "stick" closed, open, or anywhere in between. It just
stops working mechanically.

Thanks for the explanation.

2. What's the effect of having a thermostat that refuses to open? I
am asking this because I have a problem getting water coming out from
the telltale, and I have a hard time finding out the cause of this
problem, and I am wondering if a constantly-closed thermostat may cause
this problem or not.

A thermostat that refuses to open (and is stuck closed) will cause an
overheating engine. It will not affect the telltale.

OK, I can rule out the stuck-closed thermostat as the cause of my
problem of not seeing telltale from the outboard.

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.

I only ran the motor at low speed for a minute without the telltale
(and it ran fine last year when I winterize it). I don't see any paint
peeling off from the motor yet. I guess it should be fine. I will see
when I try to winterize it in the coming weekend or the next weekend.

Jay Chan