Checking thermostat

[Skin diver]

I'm coming up on my 100 hour service and was wondering how do I check my thermostat? How can you tell if it needs to be replaced?

[fairdeal]

Some here advocate simply discarding it and installing a new one.

Nonetheless, they are capable of functioning properly for many years.

Just the act of removing / replacing it is prophylactic -

forestalling corrosion of the housing around the thermostat

(a possibility, when run in seawater)

It should be closed when you see it (below 60 C)

it should not be significantly "crudded up" with "salt" or "corrosion"

then, test that it opens properly by taking it into the kitchen,

and suspending it with a wire into a pot of water on the stove

as you heat the water up to >60 C

[99yam40]

See that it opens and closes according to the spec in manual and that it moves as far as it should

[fairdeal]

I asked my Yamaha (former dealer) mechanic the other day while on the boat drilling out another gummed up pee hole assembly (by the regulator) the same question about thermostats.

He said look/check/change at 1000 hours.

Hmmm.

Well, I don't know what the previous owner did while he had it

but this is what my F225 looked like when I got it - at 750 hours

about 0.040" metal left before "eating through"

[99yam40]

I think it is a good idea to change them often or at least clean it up real good every year or 2.

there are copper parts in the ones I have looked at and if salt or corrosion builds up enough to cause a bridge from the copper to the aluminum housing you will find that pitting in the housing the stat sits in

[robert graham]

Hmmm.

Well, I don't know what the previous owner did while he had it

but this is what my F225 looked like when I got it - at 750 hours

about 0.040" metal left before "eating through"

I'd be tempted to clean that deepest/largest pit with a wire brush and apply a blob of JB Weld, let it set up good, then file smooth....better than a hole there after another .040 inch of corrosion....

[Skin diver]

Hmmm.

Well, I don't know what the previous owner did while he had it

but this is what my F225 looked like when I got it - at 750 hours

about 0.040" metal left before "eating through"

What year is your engine? That's bad for only 750 hours.

[boscoe99]

Corrosion works on calendar time, not so much on engine hours.

Put a shovel outside and don't put any operating time on it. Watch what happens to the steel.

[TownsendsFJR1300]

I had a mercury (150HP roughly?) given to me years ago as it didn't run right.

Water was getting into one cylinder. Rarely flushed...

Removed the head, water jacket cover and found a hole direct to the combustion chamber from the water jacket.

Cleaned up the hole, ground up a piece of aluminum to fit tight and had it welded in. It was easily 5/16" thick.

Worked great, boat another hull, and put them together and sold it..

[fairdeal]

What year is your engine? That's bad for only 750 hours.

This is a TXRD - mfg'd 11/04. Its on a 2005 boat that I bought "second hand" in 2014.

The boat was in excellent shape,
the Yamaha looked good overall and had been "checked out" by the dealer,
who had done a compression check, impeller, lube, etc.

And it ran great - neither overheat nor cold.

However, when I went to have a look at the thermostats, a few months later:

I had to use a pry bar

they were solidly encrusted into the housing with white "salt"

so obviously, they had not been "removed for inspection yearly"

maybe, never before?

[zenoahphobic]

This is a TXRD - mfg'd 11/04. Its on a 2005 boat that I bought "second hand" in 2014.

The boat was in excellent shape,
the Yamaha looked good overall and had been "checked out" by the dealer,
who had done a compression check, impeller, lube, etc.

And it ran great - neither overheat nor cold.

However, when I went to have a look at the thermostats, a few months later:

I had to use a pry bar

they were solidly encrusted into the housing with white "salt"

so obviously, they had not been "removed for inspection yearly"

maybe, never before?

The shame about this is that it probably would have made little difference if you replaced the thermostats regularly as electrolisys has caused this corrosion.

Except for the fact that the cavity would have had the salt etc cleaned out every time, enabling flushing water to aide in keeping the salt washed away.

[rodbolt17]

best I recal Yamaha recommends T stat inspection/replacement every two hundred hours.

OR OR OR OR
once a year.

gotta member ponies, its hourly OR calander.

heck my F150 is 8 yrs old and has had 3 water pumps yet only has 262 hours on it.
8 or so cause I forgot it was running at the dock one day.

[capnkingfish]

Twin '02 225 TXRD's with the same cancer as you are experiencing. Boat / engines meticulously cared for. It's obvious that the recommended method of flushing the engines is not effective. We ended up making an aluminum sleeve and inserted it into the water jacket where the thermostat sits and secured it with JB weld. The other three thermostats were pulled and the surfaces required significant cleaning and a coating of JB weld to hopefully retard any further corrosion. Ran the engines today for the first time and the repairs seem to work. Only time will tell. Pull your internal anodes and check them as well. One of the four on my starboard engine looked like a piece of rock candy ( salt deposits). Very disappointing considering I felt I was flushing the engines sufficiently after each trip (15 minute flush upon returning and another 15 minute flush while the boat is cleaned up the next day).

[fairdeal]

I decided against applying epoxy to the inside of the bore;

I was imagining saltwater getting in behind it and continuing the corrosion

so I "built up" the outer surface with Marine Tex for reinforcement.


On the advice of a Honda mechanic

(apparently Hondas are susceptible to the same problem)

I painted the inner bore with chromate primer (after thorough cleaning)

and that has held up perfectly, so far: one year, ~300 hours running

[capnkingfish]

It's encouraging to hear of your success. I hope I can report the same at 300 hrs post-repair. It sure beats the 11k repair bill I was quoted to replace the powerhead.