coolant flow - (follow up to cooling diagram)

[widdowson2008]

I am tring to produce the cooling fact sheet based on FACTS, and because there will still be folk who believe the jiggle pin floats, I produced the following showing both a pic and a dimensional drawing .

The pic shows there to be no joints in the jiggle pin bulb which could suggest it to be of float type construction.
Coupled with this, I have made several attempts to make it float whilst emmersed in water. Each attempt failed.
As the pin is made of steel, and hence denser than water, the only conclusion that can be reached is that it is solid.

The drawing shows the physical dimensions of the pin and the associated hole in the stat flange. The figures shown were obtained with a vernier calliper and are accurate.

First thing to notice is that the difference in area between the pin and the hole through which it passes is 5.1mm². This is the area through which air trapped below the stat (in the radiator connection) escapes. When fitted into the housing, the jiggle pin is located at the higher end where trapped air will gather.
The only force that can cause the jiggle pin can to block this hole is for a strong flow to exist between rad side and wax bulb side, and this flow will only affect the stat through-flow temperature when the stat is closed. ie: the jiggle pin is 'going with the flow'. Personally, I don't believe this happens.

For those who believe this hole has to be blocked so that on warm up, no coolant from the radiator is allowed into the mix, consider the following. The area through which this flow passes is 5.1mm², whilst the area of the stat housing outflow to the engine is 962mm² (35mm diameter) ie 0.53%. Would this very small percentage dramatically affect the coolant temperature? No.
The conclusion I reached is that the only logical function of the jiggle pin is to bleed out any air which may be trapped beneath the stat in the rad pipe section, and that this only occurs when the stat is closed.

[mikeonb4c]

I don't think, being that the jiggle pin doesn't float, that we get too hung up over it and just accept that it is a means for allowing coolant through and to aid bleeding to a (pardon the pun) degree.

that sounds about right to me

[widdowson2008]

I don't think, being that the jiggle pin doesn't float, that we get too hung up over it and just accept that it is a means for allowing coolant through and to aid bleeding to a (pardon the pun) degree.

that sounds about right to me

FACTS and numbers Mike - the fundamental components for getting at the truth. I'm leaving the wooly bits to others.

[dave_aber]

The only force that can cause the jiggle pin can to block this hole is for a strong flow to exist between rad side and wax bulb side, and this flow will only affect the stat through-flow temperature when the stat is closed. ie: the jiggle pin is 'going with the flow'. Personally, I don't believe this happens.

If the jiggle pin doesn't "go with the flow", then why not just have a hole? I can see that if there is air on the bottom side (i.e. trapped) then the pin will drop into this space and let the air through. I also agree that the pin can't float as it is solid, so what's it for if not to block the hole under influence of the water flow?

[mikeonb4c]

The only force that can cause the jiggle pin can to block this hole is for a strong flow to exist between rad side and wax bulb side, and this flow will only affect the stat through-flow temperature when the stat is closed. ie: the jiggle pin is 'going with the flow'. Personally, I don't believe this happens.

If the jiggle pin doesn't "go with the flow", then why not just have a hole? I can see that if there is air on the bottom side (i.e. trapped) then the pin will drop into this space and let the air through. I also agree that the pin can't float as it is solid, so what's it for if not to block the hole under influence of the water flow?

Amongst the stuff I read yesterday I noticed people saying that some thermostats don't (well maybe didn't have, if it was the old days being referred to) have jiggle pins at all, and other people happily saying 'just drill a 1/8 hole - it'll do the same job as a jiggle pin''. So yes, what is it all about? From the shape of it , it does look like something that would always allow air through, but that seems to want to have some kind of crude non-return valve like function. So (whilst the thermostat is closed) if coolant flow is lazy or pulsing, it is likely to let some small volume of coolant through, but once a decent head of pressure is established, it stays shut.

Is Steve (widdowson) able to advise on which way coolant normally flows through the jiggle pin hole and/or do a crude test to see how effectively the jiggle pin stops flow through the hole when a decent head of pressure is applied? That might help determine what (if any) purpose it might have apart from letting air through.

One other question. Is the thermostat housing always fitted (on different designs of cars) so that air can rise through the jiggle pin hole?

No-one could accuse the Bongo Tribe of not thoroughly chewing over the smallest piece of meat

[mikexgough]

For those who believe this hole has to be blocked so that on warm up, no coolant from the radiator is allowed into the mix, consider the following. The area through which this flow passes is 5.1mm², whilst the area of the stat housing outflow to the engine is 962mm² (35mm diameter) ie 0.53%. Would this very small percentage dramatically affect the coolant temperature? No.
The conclusion I reached is that the only logical function of the jiggle pin is to bleed out any air which may be trapped beneath the stat in the rad pipe section, and that this only occurs when the stat is closed.

Enough said.... .... I have nothing further to add , too much has been suggested that has diverted this process already and it needs to be concluded with out further ado.....

[widdowson2008]

Hi Dave
I believe the answer to that one is in the name 'jiggle'. To move or rock lightly up and down or to and fro in an unsteady, jerky manner according to Farlex free dictionary definition (and Arkwright in Open All Hours)
If the stat is correctly installed, the 'jiggle pin' is directly in line with the heater return flow. This flow will 'jiggle' the pin which is fairly loose in the hole, thus breaking up bubbles just below the hole and encouraging the air to escape.
I can't see any other purpose for it.
I have read of folk drilling a small hole in the stat flange, presumably for the same purpose. (Just seen Mikes input and he seems to remember the same)

Mike
The flow is upward as viewed on the recent sketch, and I have no idea about the pin orientation in other cars, but I would think it would be the same - it makes sense to have the escape at the highest point don't you think.

[g8dhe]

Did some googling and there do seem to be sum Mazda OEM's that don't have a Jiggle pin or hole see http://michael-david-palmer.com/gallery ... _itemId=26

also this little comment (click it for the link to reference);

If you have a jiggle pin in your old thermostat, carefully bend the tabs to remove it. Install the jiggle pin in the new thermostat so that it will seal for flow toward the radiator.

The emphasis is mine and perhaps explains why the Jiggle pin and not just a hole is require, it seals for reverse flow and also as Steve suggests above assists breaking up any bubbles or even crud from the radiator that might block the hole.

[widdowson2008]

Did some googling and there do seem to be sum Mazda OEM's that don't have a Jiggle pin or hole see http://michael-david-palmer.com/gallery ... _itemId=26

also this little comment (click it for the reference);

If you have a jiggle pin in your old thermostat, carefully bend the tabs to remove it. Install the jiggle pin in the new thermostat so that it will seal for flow toward the radiator.

The emphasis is mine and perhaps explains why the Jiggle pin and not just a hole is require, it seals for reverse flow and also as Steve suggests above assists breaking up any bubbles or even crud from the radiator that might block the hole.

Not sure what you're saying here Geoff - 'reverse flow'?
Are you sure the above quote is refering to the Bongo type system with the stat on the flow TO the engine as opposed to the more 'conventional' system - flow FROM the engine to rad?

Just read the jiggle pin link (missed it first time) Seems to be saying something similar to my thinking, but again I stress, to compare other systems can be misleading unless they are exactly the same as a Bongo.

[g8dhe]

I was really trying to think what the function of the Pin itself was as opposed to just having a hole, if its just to let trapped air out then a hole is all that is needed, why put the Pin in ?

[widdowson2008]

I was really trying to think what the function of the Pin itself was as opposed to just having a hole, if its just to let trapped air out then a hole is all that is needed, why put the Pin in ?

As previously said......
I believe the answer to that one is in the name 'jiggle'. To move or rock lightly up and down or to and fro in an unsteady, jerky manner according to Farlex free dictionary definition (and Arkwright in Open All Hours)
If the stat is correctly installed, the 'jiggle pin' is directly in line with the heater return flow. This flow will 'jiggle' the pin which is fairly loose in the hole, thus breaking up bubbles just below the hole and encouraging the air to escape.

[The Great Pretender]

I was really trying to think what the function of the Pin itself was as opposed to just having a hole, if its just to let trapped air out then a hole is all that is needed, why put the Pin in ?

I have to agree, turn the stat over and look at it the way it would be fitted on the outlet of the head and the pin takes on a meaning.

I may as well get shot for a sheep as a lamb so here is my take on how I think about the cooling system.
Each part of the system is a leg, some have sub legs. The only way to have flow through them all is by having the same resistance across each off them. Accept that and it gets easier.
The system can now be divided into two main sections, engine to heaters (primary) and engine to radiator(secondary) although there is some cross mixing they work mainly independent depending on thermostat position and that is controlled by flow from the primary side at all times.
When flow over the stat is hot enough to open it the primary flow is still in control so minimal flow from rad.
As heat is slowly transferred the stat eventually closes the bypass (the resistance link between primary and secondary systems) only then does the system work as one with equal resistance throughout. This is the state required to hopefully fully bleed the system.

Seemples.............????

[dandywarhol]

I haven't seen a bongo stat so unable to add to the thread but seen/fitted plenty of stats with nylon pins in them which float and "jiggle" as mentioned, then seals against the stat to avoid coolant to pass until the stat has opened

[missfixit70]

I was really trying to think what the function of the Pin itself was as opposed to just having a hole, if its just to let trapped air out then a hole is all that is needed, why put the Pin in ?

I have to agree, turn the stat over and look at it the way it would be fitted on the outlet of the head and the pin takes on a meaning.

I may as well get shot for a sheep as a lamb so here is my take on how I think about the cooling system.
Each part of the system is a leg, some have sub legs. The only way to have flow through them all is by having the same resistance across each off them. Accept that and it gets easier.
The system can now be divided into two main sections, engine to heaters (primary) and engine to radiator(secondary) although there is some cross mixing they work mainly independent depending on thermostat position and that is controlled by flow from the primary side at all times.
When flow over the stat is hot enough to open it the primary flow is still in control so minimal flow from rad.
As heat is slowly transferred the stat eventually closes the bypass (the resistance link between primary and secondary systems) only then does the system work as one with equal resistance throughout. This is the state required to hopefully fully bleed the system.

Seemples.............????

Fantastic simply put description , wish I could have worded it that well, it scares me when we agree Mel

[Northern Bongolow]

ABSOLUTELY SPOT ON well said that man great pretender.

ady.