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

wrote in message
ups.com...


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


I don't know if you actually ran it for a full minute or just for a "little
bit" of time.
The reason I mention it is that I recall that water flowing from the
telltale doesn't happen right away when you start the engine. It takes some
time (don't know the exact period and probably varies from engine to engine)
for the water pump to get the water up to the head and out the exhaust and
telltale. I know my outboards would initially run for (guessing) 10-15
seconds before the telltale started flowing.

Eisboch

Eisboch wrote:
wrote in message
ups.com...


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


I don't know if you actually ran it for a full minute or just for a "little
bit" of time.
The reason I mention it is that I recall that water flowing from the
telltale doesn't happen right away when you start the engine. It takes some
time (don't know the exact period and probably varies from engine to engine)
for the water pump to get the water up to the head and out the exhaust and
telltale. I know my outboards would initially run for (guessing) 10-15
seconds before the telltale started flowing.

Eisboch

Well, this was something like 30 seconds to one minute. I didn't look
at the clock. It was definitely much longer than it should take for
the telltale to show up based on my prior experience in winterizing my
motor. I don't remember how soon the telltale should show up right
after starting my motor. But when I see someone's past post about
seeing the telltale a few seconds after starting the motor, I have a
feeling that this is about right.

As mentioned in one of my reply, the old thermostat actually is not
broken. This means the thermostat has nothing to do with the "not
seeing telltale" problem. I really have no idea why the telltale
doesn't show up (the thermostat is OK, the impeller looks OK, the water
passage way in the powerhead and the telltale hose is not blocked...).
Now, my theory is that the water pump is missing the sealing ring on
top of the water pump housing, and the water goes all over the place
instead of going up to the powerhead. I will test this theory when I
get the lower unit back from the dealer. Hopefully, I can finish
winterizing the motor in this weekend.

Jay Chan