Corroded hole through wall of thermometer housing

[Maverick70]

Hello,

Pulled thermometer out to replace and came two problems.

1) Broke off one of the bolts.

2) The side wall was pretty corroded and brittle and part of it actually crumbled through.

I'm a novice here, so trying to figure out what to do. The rest of the motor looks very clean and was running well and I've always flushed after every use, but I'm not sure when or if the thermostat was ever changed last. Also not sure how it was treated before I got it in 2012 (the motor is a 2007). The corrosion seemed to be very localized to one pocket right next to the thermostat, but of course there could be similar issues elsewhere hidden.

Is it time to start saving for a new motor, or can this be repaired? It looks like the thermostat housing is part of the main block, so can't be simply replaced. Not sure if it can be welded or can use something like Marine Tex to fill hole.

2007 70hp 2 stroke 70tlr

Any insight would be greatly appreciated.

Best,
Keith

[boscoe99]

Can we get a brand and model for the motor please?

[fairdeal]

I think this view is better:

hosting image

[Maverick70]

2007 70tlr two stroke

[boscoe99]

Ever tried to view an upside down or side ways photo on a Kindle? As fast as you rotate the Kindle to view the photo it reorients the damn photo. Reminds me of my dog chasing his tail.

[99yam40]

I had the same thing happen on my C40.
I had a welder use a high frequency welding machine on it from the outside.
he had a very hard time closing up the hole, but he finally got it done,
the material it is made of plus the corrosion/contaminants in the metal kept blowing holes in the molten metal as he welded.

I used some marine JB weld Epoxy on the inside to fill and shape the hole so the stat fit back in well.

It has held up so far, but who knows how long it will last.

I think the copper in the stat bridged to the side with corrosion and that accelerated the deterioration of the aluminum.

In my opinion Pulling the stat and cleaning that area more often would have helped keep this from happening

[boscoe99]

Given the ease of access to the damaged area, if that were my motor I would have it TIG or MIG welded. With maybe a thin section of aluminum tubing press fit into the thermostat bore first, if it will not interfere with the insertion of the thermostat. To act as a liner of sorts.

Others have been known to use JB Weld or similar type product. Clean the hole thoroughly. Use a piece of plastic inside the bore to help hold the JB Weld in place and get it to conform to the inside of the bore cavity. The plastic will come out once the stuff has hardened.

Once any type of repair has been made put the repaired area on your list of inspection items to be examined periodically. It is not good if salt water sprays out of the hold and drenches the electrical stuff down or if it gets sucked into the intake system.

The bore in which the thermostat(s) resides has been known to be a hot spot item for a number of Yamaha models. Too bad they don't talk about thoroughly inspecting the thermostat bore when the thermostat is removed yearly for its inspection and/or replacement.

You do pull the thermostat yearly of course. Correct?

[boscoe99]

I had the same thing happen on my C40.
I had a welder use a high frequency welding machine on it from the outside.
he had a very hard time closing up the hole, but he finally got it done,
the material it is made of plus the corrosion/contaminants in the metal kept blowing holes in the molten metal as he welded.

I used some marine JB weld Epoxy on the inside to fill and shape the hole so the stat fit back in well.

It has held up so far, but who knows how long it will last.

I think the copper in the stat bridged to the side with corrosion and that accelerated the deterioration of the aluminum.

In my opinion Pulling the stat and cleaning that area more often would have helped keep this from happening

Your opinion is shared. A gram of prevention in the form of spotting, removing and repairing internal corrosion early would be worth a kilogram of cure in the form of having to weld a hole closed.

[Maverick70]

I will now. To be honest, I have been taking the boat to the local boat shop every year and asking them to do whatever they recommended. I don't think that they had been pulling and checking the thermometer. I told myself that I will now start doing the annual maintenance and this will be one of the things that will be on my list. It does look like the proximity of copper accelerated the corrosion here.

[TownsendsFJR1300]

Looks like either welding or an epoxy to repair that hole..

I'd go to a GOOD prop shop as they weld thin aluminum blades (props) and should be able to clean that up and close it as well..

Not terribly long ago, we had a Suzuki LU welded that was paper thin. We had an machine shop do that, but if I had to do it again, the prop shop is the way to go..
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After:


BTW, I had a mercury (given to me) which had a hole (corrosion) from the combustion chamber direct into the water jacket. (the PO, my neighbor Never flushed).

The hole was large enough that I cleaned up the area for the welder, made a small chunk of aluminum to fit and he welded it in. Ran great, boat a hull, installed and sold...