Are Sierra thermostats OK?

[collectorinspector]

quote FrankR:

But I still go back to my original question. If the ‘stat does not have a notched poppet, how can the water flow up from the cavity that it sits in, and if it can’t flow, how does it present itself to the pellet? Unless the gap in the cap is supposed to leak enough to let some through. Seems iffy to me. I still think it needs a notched poppet.

No "iffy".

Thermostats control the varying flow of water through a block in a lump, or just control the maximum head temperature letting general flow do the rest as per what the maker intended.

Thermostats do not control air which is displaced from a system such as those discussed under water pump pressures throughout the system.

No wheel to invent here.

There have been some excellent posts above so maybe revisit them aye.

I maintain that a thermostat is a vital part of the whole.

C.I.

[frankr]

Nuts! Y’all (I’m Southern) aren’t listening to my question. I fully understand how the system works and even tore down a powerhead to illustrate how it works. Furthermore, I am not disputing the need for a thermostat.

The Original Poster questioned the absence of a bleed hole in a new thermostat he bought. Others later assured him that the bleed hole is not necessary. I maintain that it is necessary, thus my question.

I say that the bleed hole is necessary to allow a bit of water to flow past the thermostat heat-sensing pellet (and to purge the air from the water jacket surrounding the cylinders).

Examining the cylinder head that I just tore down, there is no outlet from the thermostat cavity except for the bleed hole in the thermostat poppet. If there is no outlet, water can’t flow into it. And if water can’t flow into it, the thermostat can’t sample it.

Unfortunately, I don’t have a thermostat, but it is kind of obvious that if I did have one, it and it’s rubber seal would sit on the flat surface surrounding the thermostat cavity and be pressed down tightly by the cap. Therefor the only way through the area would be the bleed hole in the poppet.

The public is watching this, and we shouldn’t even be arguing about it here. I’m signing off.

[collectorinspector]

Well done Frank.

CYA Mate.

C.I.

[Casey Lynn]

Frank, bring your block to the Suwanee and we will get it figured out. Deal?

[frankr]

quote Pappy:

Frank, bring your block to the Suwanee and we will get it figured out. Deal?

I would but I can’t make it to Suwanee. Next meet I can do will be Lake Shipp

[amuller]

OK. I’m just trying to learn more about this, not start a squabble or promote Amazon as a place to buy stuff. I’d feel more comfortable with a bleed through the thermostat poppet, but maybe it works out in practice without one….

Never got an answer to my question about what the blank fitting passage in the thermostat cover plate is for (306198).

Can see it here: http://www.ebay.com/itm/NEW-NOS-OMC-Joh … 0608304715

I’ve wondered if this could be for a pee-hole (telltale) and, if so, would that serve as a bypass?

[fleetwin]

Not to worry amuller, we are usually just looking for an excuse to be cranky!
I’m not sure just what you are asking about the ebay thermostat cover…So, please re-ask your question….In any event, the early style thermostat cover was designed way before the overboard indicators/pee-holes were introduced late in the 70s. So, I’m thinking whatever the blank passage you are referring to is just part of the manufacturing process.
I too feel that most thermostats need a bit of a bleed to make sure the block is not air bound until the thermostat somehow opens….I will have to look at one of the new BRP SS thermostats when I get home…

[frankr]

amuller, the motor I tore down has a bit different thermostat cover. It does not have that passage across the top. However, I think I can answer the question, hopefully without getting into another discussion. Look at the pictures I posted earlier and note the flow that is not thermostat controlled. See where it comes up from the head, goes through a groove on the bottom of the cover plate, then back down the backside of the head?

OK, the cover on e-bay is used on a different motor (maybe 10hp???). On that one, the uncontrolled water comes up from the head, goes through the passage you are asking about, then down directly over the center of the thermostat. When the thermostat is closed, it is free flow for the uncontrolled water passage. But when the thermostat opens fully, the poppet rises and partially blocks the flow from that passage across the top. Because that flow is partially blocked, water pressure (and flow) from around the cylinders increases, which increases the cooling of the cylinders. (Something to consider when contemplating whether or not the ‘stat is needed)

Following is the 6hp ‘stat cover that I tore down

image hosting free

[amuller]

The last post I wrote disappeared, which happens about 25% of the time on this board. I must be doing something wrong. It wasn’t valuable enough to do over, but I do have another thought:

If part of the flow control action is that the poppet bears on the inside of the cover plate when the stat opens, it makes sense that the stat would have, and need, a poppet spring-loaded onto the spindle. I don’t believe the Sierra SS state I put in has that feature. Unless there is equivalent flexibility built into the stat in some other way, it seems to me that the new Sierra state is not equivalent to the original in two ways: (1) lack of a slot in the poppet, and (2) lack of spring loading of same.

[frankr]

That is a subject I don’t have an answer to.

Btw, I am not a moderator, but I’ve had postings disappear also. I assume it was because I hit the submit button at the same time as somebody else did.

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