"Custom" thermostat?

[walleye1]

put a stainless steel pipe plug in it.

[boscoe99]

If you decide to remove this fitting and tube, just plug the fitting hole with JB Weld.....who knows how much$$$ Yamaha gets for that thermostat cover?

Not as bad as I was expecting.
https://www.boats.net/product/yamaha...5e97fe03b4c0d6

[TownsendsFJR1300]

Not as bad as I was expecting.
https://www.boats.net/product/yamaha...5e97fe03b4c0d6

What's the hole in the second picture of that link for? Dead center...

[boscoe99]

What's the hole in the second picture of that link for? Dead center...

Don't know. It is not for the Yamaha pressure or temperature sender. Maybe just to some some aluminium or weight? Wild eyed guess on my part of course.

I am just guessing that some yahoo decided to take the tell tale water from the top of the block as opposed from the exhaust cover. Maybe he felt good when feeling the temperature of the water. He might have owned a Mercury which is a hot pisser as opposed to Yams being cold pissers. Maybe since it is a fresh water motor he is using hot water to make his pot of tea.

[TownsendsFJR1300]

Don't know. It is not for the Yamaha pressure or temperature sender. Maybe just to some some aluminium or weight? Wild eyed guess on my part of course.

I am just guessing that some yahoo decided to take the tell tale water from the top of the block as opposed from the exhaust cover. Maybe he felt good when feeling the temperature of the water. He might have owned a Mercury which is a hot pisser as opposed to Yams being cold pissers. Maybe since it is a fresh water motor he is using hot water to make his pot of tea.

NOOO....The NEW PART.. The second pic on your parts link, there's a hole from the factory there! ???

[mitch184]

I did run across a guy who mentioned having the tell tale up high like that helps get air out of the block faster. Also helps makes sure you don’t get air pockets trapped in the system.

makes sense I guess??

[boscoe99]

NOOO....The NEW PART.. The second pic on your parts link, there's a hole from the factory there! ???

Yes, I know. I saw it. I don't know what it is for. I guessed that it is for saving aluminium or weight.

The OP's motor has the same hole.

[TownsendsFJR1300]

Looking at the parts diagram, (part #44), it doesn't show anything (or a hole) going there.

Perhaps that close up pic (from your link), it's just cast into the piece and doesn't have a hole that goes all the way thru STOCK.

https://www.boats.net/catalog/yamaha...nder-crankcase

That wider end (where that "stock hole" is), is on the end of the PCV valve. The thermostat is at the other protrusion..

Perhaps to hold the PCV valve spring from moving about? Not fully drilled thru? Odd to say the least..


The Op's hole is at the thermostat end...(someone definitly modified that)..

[walleye1]

It is a dimple to line up the poppet valve spring.

[mitch184]

It is a dimple to line up the poppet valve spring.

That’s it I’m 99% sure

[boscoe99]

The internal part is that which holds the spring in place. The question is, as I understand it, why is there a hole on the outside of the housing. The dimple could have been solid. Apparently it is hollow. Why?

Was there some intent many many moons ago to install a sensor or probe of some sort into the hole? The dimple then could have served at leas two functions. On the inside it retains the spring in place. On the outside it (fill in the blank here).

Where the hell is fairdeal?

[panasonic]

Perhaps the OP can post a picture of the exhaust cover. Maybe the nipple for the telltale was broken off the cover or it is plugged up internally. Almost looks like there is a black hose coming from the left hand side in the picture that would have been the original telltale hose?

I don't see any reason to have a hose coming from the thermostat housing in terms of some kind of cooling modification. I think it was put there to act as a telltale because there is something wrong with the original one.

[holmen78]

Maybe previous owner wanted to confirm function of popit valve? I don’t know when the water pressure is opening the valve. Maybe he wanted to see when theromostat is opening? That mod won’t affect cooling much because the water from there goes between head cover and head cover gasket down to lower part of the block. In attached pic you can see the head cover gasket throug the 4 holes where the water from thermostate and pop it valve goes.

The thermostate is missing in first picture.

[TownsendsFJR1300]

Maybe previous owner wanted to confirm function of popit valve? I don’t know when the water pressure is opening the valve. Maybe he wanted to see when theromostat is opening? That mod won’t affect cooling much because the water from there goes between head cover and head cover gasket down to lower part of the block. In attached pic you can see the head cover gasket throug the 4 holes where the water from thermostate and pop it valve goes.

Heck, as I see it, if anything it's allowing water AWAY from where it SHOULD BE, which is not good..

[mitch184]

The exhaust cover has one nipple with a hose coming off. However the hose has a plug in it so nothing flows out of it.

So Does the water flow from the bottom up to the thermostat and then in? Or does it come out of the thermostat then down to the poppet? I feel like I should know this.