coolant flow - (follow up to cooling diagram)

[rita]

Can't air get trapped between the bottom of the radiator and the thermostat ?
Your diagram
shows that it rises upwards, if the thermostat hasn't got an air hole, or it gets blocked if it does have one, then air will be trapped until the Thermostat opens, hence needing to make sure it does open and a hot lower hose shows that it has and that air isn't trapped.

That's what I thought, and indeed, it was the very reason I produced that drawing, to show where air could get trapped.
....and then.........
I examined a thermostat very closely (in fact, took one apart). What I found was that not only was the 'jiggle pin' a very loose fit in the main flange, it is also in the direct line of fire from the heater return flow coolant (providing the stat has been correctly fitted). Jiggle pin shaft is 1mm diameter fitting into a 3mm hole - what in engineering terms is a 'piss fit'. I don't think a 3mm hole could be tolerated anywhere else on the pipework. Conclusion? - designed to leak.
As far as 'getting blocked' is concerned, of the 7 stats I have tested, all the jiggle pins were loose (as per a new stat)
When the engine is running, the pump creates a turbulent flow within the stat mixing chamber, which in turn gives the 'jiggle pin' a fair old buffering. Because I cannot physically see inside the housing during normal working conditions, I can only assume that any air trapped below the stat flange will take its easiest route, and that would be through the jiggle pin hole. I hate assumptions, but I honestly believe that this is the true function of the jiggle pin - a bleeding aid. I cannot think of any other possible purpose for it being there. Always open to ideas though.

Most thermostats have a Jiggle pin. Its function is to allow trapped air past a closed thermostat as a build up of air in front of the wax capsule could cause engine damage. The wax capsule relies on coolant to relay heat to operate. If air was surrounding the capsule and the engine was at operating temperature, the stat would remain closed and cause the engine to overheat.

[widdowson2008]

Any thoughts though on whether a hot bottom hose might be indicating poor cooling instead of good circulation?

I agree with most of what Kirsty has said - very well explained, but again I find myself sat on the fence, listening.
One thing Kirsty is constantly banging on about (sorry Kirsty, but you do and long may it continue), and I must stress that I fully agree, is that if you reach a point where a coolant change is necessary, then clean the system properly, fit the correct parts and add the correct coolant. On this issue, I am certainly NOT sat on the fence.

Where did this 'bottom hose must be hot' come from? Not the Mazda manual. Who coined the phrase?

Currently, I have one foot in Mikes camp myself (re:poor cooling...good circulation), but prepared to be swayed. Why? If you took the rad out of the equation and connected the top and bottom hoses together, what would happen? The bottom hose would get hot. And surely this could be simulating the real life scenario if the rad was partially blocked, but a hot bottom hose appears to be what folk are looking for. Doesn't add up, unless I am missing something very simple

Not really convinced that sealing face inside the stat must be clean is a valid issue. Reason I say this is that the force keeping the disc in the closed by-pass state is 22kg.f @ 96degC, rising to 30kg.f @ 98deg.C (test figures) That is one hell of a force on that small area, but again, prepared to be swayed given the numbers.

[g8dhe]

Most thermostats have a Jiggle pin. Its function is to allow trapped air past a closed thermostat as a build up of air in front of the wax capsule could cause engine damage. The wax capsule relies on coolant to relay heat to operate. If air was surrounding the capsule and the engine was at operating temperature, the stat would remain closed and cause the engine to overheat.

But in the Bongo the thermostat has the wax cylinder ABOVE the lower hose, in the flow of the bypass at all times hence the air is trapped below it.

Do any of the pictures show the Jiggle pin ? I've been looking and can't see it in any of the pictures or diagrams, its only been spoken about ?

[widdowson2008]

Most thermostats have a Jiggle pin. Its function is to allow trapped air past a closed thermostat as a build up of air in front of the wax capsule could cause engine damage. The wax capsule relies on coolant to relay heat to operate. If air was surrounding the capsule and the engine was at operating temperature, the stat would remain closed and cause the engine to overheat.

Thanks for that - yet a little further along the road of understanding

[widdowson2008]

Most thermostats have a Jiggle pin. Its function is to allow trapped air past a closed thermostat as a build up of air in front of the wax capsule could cause engine damage. The wax capsule relies on coolant to relay heat to operate. If air was surrounding the capsule and the engine was at operating temperature, the stat would remain closed and cause the engine to overheat.

But in the Bongo the thermostat has the wax cylinder ABOVE the lower hose, in the flow of the bypass at all times hence the air is trapped below it.

Do any of the pictures show the Jiggle pin ? I've been looking and can't see it in any of the pictures or diagrams, its only been spoken about ?

Jiggle pin - viewed from underside (rad side) genuine Mazda KL01-15-171A stat (still in one piece Ian )

[g8dhe]

Thanks Steve, I guess some of the pattern ones don't have that then unless they all just happen to have been photographed at the wrong angle !

[widdowson2008]

Thanks Steve, I guess some of the pattern ones don't have that then unless they all just happen to have been photographed at the wrong angle !

All the ones I have tested have one. They were all Blueprint except one which was a Ford.
Probably no one thought the little dangly bit worthy of a pic.

[mikeonb4c]

If air was surrounding the capsule and the engine was at operating temperature, the stat would remain closed and cause the engine to overheat.

May need to be a bit careful to qualify that? It is quite possible (likely, in a confined space with no external cooling) that heat will conduct from coolant to air and it will reach the same temperature as the coolant. The issue really I'd have thought is how much air may damp (cause a delay) in the transmission of heat from coolant to wax in the stat.

[widdowson2008]

....
conclusion imho is that the jiggle pin is actually a float and only opperates properly when in contact with water ??????

ady

Sorry but I don't think so. It's solid steel, not a hollow float construction. The only way it can block the hole would be if there were a swift flow of coolant going past it, and even then I don't think it likely. ....but I could be wrong

[widdowson2008]

If air was surrounding the capsule and the engine was at operating temperature, the stat would remain closed and cause the engine to overheat.

.

If the capsule were surrounded by air, it would mean that both the heater and cylinder head coolant return circuits had failed and the head was full of air. If this happened, the head would be history surely?

Can I get back to the original question which was 'why must the bottom hose be hot to bleed properly'
The reason I am persisting is the following:
For this hose to be hot, the following circumstances must exist:
1 - The stat must be fully open.
2 - The rad must be full of hot coolant
It follows that the cooling system is well out of the stat control range and in a dodgy place because the engine is calling to be cooled and the rad can only deliver hot coolant (thus keeping the stat open)
Isn't this potentially dangerous?

[missfixit70]

Looks like people are not understanding how the cooling system works again
The stat wax cylinder is above the stat & in constant flow of water circulating around the heaters etc, if it's in air then your system really is F***ed.

As for the theory that hot bottom hose menas a goosed sytem, if you are stationary ie when bleeding (no airflow, no fans), the rad is only going to have a small cooling effect, so hot coolant going in from a properly warmed engine 90 degrees plus, is going to be coming out the bottom at 70 degrees plus if everything is working as it should ( mine is about 15 degrees drop & I know my system is spot on).

I can't be arsed explaining it again I've already done it several times, this is just going round in circles now going over ground that's already been covered, so I shall leave you all to it.

[missfixit70]

If the capsule were surrounded by air, it would mean that both the heater and cylinder head coolant return circuits had failed and the head was full of air. If this happened, the head would be history surely?

Can I get back to the original question which was 'why must the bottom hose be hot to bleed properly'
The reason I am persisting is the following:
For this hose to be hot, the following circumstances must exist:
1 - The stat must be fully open.
2 - The rad must be full of hot coolant
It follows that the cooling system is well out of the stat control range and in a dodgy place because the engine is calling to be cooled and the rad can only deliver hot coolant (thus keeping the stat open)
Isn't this potentially dangerous?

When you are bleeding it , it is stationary, as it would be in a traffic jam, with no airflow, the temp will rise to a point where the stat is fully open as I described earlier, if it continues to rise, that triggers the fan/s (which is part of the control system) which brings the temp back down again, simple
All perfectly safe & a good opportunity to establish whether your system is working as it should when called to operate at the top end ( which a lot don't ever do, which is why when after 6 months of pootling around quite happily not having to call on this "top end" of control, the bongo gets loaded up with kids, in-laws luggage & a caravan then overheats on the motorway )

[dandywarhol]

If the capsule were surrounded by air, it would mean that both the heater and cylinder head coolant return circuits had failed and the head was full of air. If this happened, the head would be history surely?

Can I get back to the original question which was 'why must the bottom hose be hot to bleed properly'
The reason I am persisting is the following:
For this hose to be hot, the following circumstances must exist:
1 - The stat must be fully open.
2 - The rad must be full of hot coolant
It follows that the cooling system is well out of the stat control range and in a dodgy place because the engine is calling to be cooled and the rad can only deliver hot coolant (thus keeping the stat open)
Isn't this potentially dangerous?[/quote]

As Mizzzy says - the stat is opened by the coolant above the stat getting hotter than required - this opens the stat and allows COOLER coolant to circulate from the radiator - I can't see anything potentially dangerous about it. The stat regulates the system's temperature, full stop.

[mikexgough]

There is one area I still can't get my head round and that is the bleeding procedure.
What I can't understand is why it is necessary to get the bottom hose hot. What does this PHYSICALLY do/prove. (apart from the obvious - getting the engine VERY hot)

It is widely stated that to bleed the system fully, the bottom hose needs to be hot, but no one has actually said why.
I know there are folk who successfully bleed their Bongos without over-revving, so I would like to hear from the pro-revving side.

[widdowson2008]

quote]

As Mizzzy says - the stat is opened by the coolant above the stat getting hotter than required - this opens the stat and allows COOLER coolant to circulate from the radiator - I can't see anything potentially dangerous about it. The stat regulates the system's temperature, full stop.

TOTALLY AGREE WITH KIRSTY - NEVER DISPUTED THAT PART - EVER
With all queries regarding cooling, sooner or later, things are taken out of context, and that is precisely what has happened here. However, with current temperature monitoring tests being rigged up on a healthy Bongo and data expected to start rolling in in a couple of weeks, I may be in a position to answer my own query.