coolant flow - (follow up to cooling diagram)

[Northern Bongolow]

the best i will do is get it out in the morning and see what i can see in the inlet/outlet.and thats it

[The Great Pretender]

I wondered if "superheat" was the wrong term to use...........................I mean more of your second explanation - very hot air.

Trapped air, like trapped wind, although how long does human gas stay trapped for can eventually try to rise to the highest point I imagine, and if air is present in the system (with the exception of the expansion/degassing tank because it's higher than the engine) then the coolant cannot circulate properly IMO. I recall trying to get a Rover 25 engine bled and eventually found a bleed valve in the system - until that was opened and the air purged out the engine just continually overheated to a dangerous level. I guess it's much like having an airlock in your house central heating system - until its bled of air the radiator remains cool, once bled the coolant can circulate and in a vehicle's case, dissipate the heat via the pipes and matrices.

A heater martix is exactly like a mini radiator with core tubes.

Love it, lets start with the central heating system. Early system relied on cold water displacing lighter hot water to circulate just like early low powered engines. This required an upward or horizontal path for flow. Just as air does to escape. A modern pressurised central heating system works with up to 45psi (3bar) but as Dandy says you need to bleed off the air, pressure will not move it.
Now for trapped 'wind'...................... Pressure build up escaping............Fart............has an escape route,why? It is not in a sealed system.

IMHO it is extremely difficult to remove (if not impossible) all air from the cooling system.
Localised boiling around the exhaust valves (the hottest part) is difficult to control, slow moving high pressure coolant offers the best protection, unfortunately the Bongo doesn't do this. A restrictor in the outlet of the head would offer protection.

[widdowson2008]

Hi TGP
'A restrictor in the outlet of the head'? How would that work/help then?

BTW Ady - I knew you wouldn't let me down. Perhaps when you see its poor, unserviceable condition, you will see the sense in giving it the chop.
I did say perhaps. (please)

[The Great Pretender]

Hi TGP
'A restrictor in the outlet of the head'? How would that work/help then?

Reduce speed,increase pressure,raise the boiling point and improve heat transfer.

[widdowson2008]

Reduce speed - yup
increase pressure - yup - How much?
raise the boiling point - yup - again, how much?
improve heat transfer - explain yerself (to a thickie)

[The Great Pretender]

Reduce speed - yup
Ok, you understand the concept.
increase pressure - yup - How much?
Depends on the restrictor.
raise the boiling point - yup - again, how much?
Depends on the pressure supplied by the restrictor.
improve heat transfer - explain yerself (to a thickie)

Nuff said?

[widdowson2008]

Can we carry this on tomorrow? System keeps crashing when I try to reply

[Ron Miel]

Went to bed, after my last posting plus a quick reply to a PM from Steve. Woke at 5:30 for a comfort break, and was still thinking about this bleeding subject. How can I get release? I know, a bleed tube - I think I can verify that below!

My most recent post (and the earlier one it paraphrased) were both deliberately over-simplified by working up a hypothesis from basic principles, while not pouring over Steve's Bongo colant flow animations as such - bit like all the good relevant stuff on central heating systems, farting, Rover (who?) 25's and so on, while I slept.

Assuming my hypothetical musings did make some sense, let's try to refine the thinking from there:

1.) Of course my contention, that air blockage restricting coolant flow TO the head was the most rapidly catastrophic situation, was incomplete. Any air blockage which severely restricted coolant flow TO or FROM the head would cause thermal runaway, as described. So, I should have said restriction of coolant flow THROUGH the head.

2.) Also, of course, the most terminal air blockage in that context would be one which either filled the radiator top tank with air, or one which blocked off the top hose somewhere between engine and radiator. Either of these would terminally prevent dissipation of coolant-transferred engine heat by radiation to the atmosphere, from the radiator. Stage 3 of the coolant refill process (after Stage 1, rad and therefore top hose cold-filled to the brim then sealed, and Stage 2, expansion tank cold-filled to the flange but left open), when the engine is run with the bleed hose elevated and unbunged, is specifically intended to reduce those possibilities, by bleeding off any still circulating trapped air before it can reach and block either the top hose or the rad top tank. Omit stage 3 at your peril.

3.) The question then remains whether sufficient trapped air can then stll linger in the system to circulate under pumping to a blockage point anywhere - but still particularly to the rad top tank or top hose, although probably not exclusively there. Where else could it have that disastrous effect of severely restricting coolant flow through the cylnder head, and causing thermal runaway? I'm still not looking at flow animations, as that question is probably best answered by peeps who know the physical characteristics of the Bongo's veins and arteries better than I do.

Talking of veins and arteries, the human gas system, as stated above, is not sealed, so we gain relief by fart or belch - the Bongo bleed stage 3. However, Mr Munkey's recent brilliant analogy (in another thread?) is also very relevant. Human blood (with entrained-oxygen) circulation is a sealed system, and a blockage in a Bongo's cooling system can be terminal in the same way as a blood clot travelling to the heart or brain can be - the Bongo risk if Bongo bleed stage 4 (revving/de-gassing) is not carried out well. I just don't think though that a Bongo air block needs to actually reach the cylinder head to do its worst, as Mr M suggested.

Need a bit more shuteye, at this point!

[widdowson2008]

Thanks Ron - think I understand.

As far as I can see, the air collection points (danger zones) in order of criticallity (is that a word?) are: (correct me if I'm wrong)
1 - Cylinder head
2 - Radiator top
3 - Expansion tank
4 - Heaters

On filling, the radiator and expansion tank can be SEEN to have been filled, so for the moment, let's leave these out of it.
We are not entirely sure of the possible volume of air trapped in the heaters (YET - experiments are currently being carried out in Bulgaria as we speak - I jest you not). The results sould be confirmed by Ady later on today. (separate experiment), so I'll be back on this one.

We now know for sure that the cylinder head (on filling) contains trapped air, and we can even quantify this. Under current bleeding methods, some of this air is expelled via the bleed tube, but not all.
The ONLY path for the remaining trapped air to get out is through the top hose connection, and this involves switching the engine on and pumping/shoving the air downhill (due to pipe layout) before it can escape through the radiator/expansion tank.
THIS is the air I can garauntee to get rid of (simply) without even switching the engine on.
So, all we need to concern ourselves about is the air in the heaters.

I'll wait to see if I get shot down here before moving on (or getting kicked out)

[dave_aber]

I'm with you 100% so far.

Are we heading to a couple of added bleed points on the 2 heater matrices?

[widdowson2008]

I'm with you 100% so far.

Are we heading to a couple of added bleed points on the 2 heater matrices?

Depends on exactly what the outcome of the heater tests come up with (hopefully Helen and Ady are working on that now - results imminent I hope)
Its the head I'm more focussed on clearing ATM.

Sorry it's slow but I don't want to miss owt if I can help it.
One step at a time

some of this air is expelled via the bleed tube, but not all.
I'm also working on a diagram which explains this. At the same time, looking at Chells bleeding video to try and capture the moment this happens. (just to tie it all together)

[Ron Miel]

Your latest post seems to give an answer to the question I posed in my point 3.), Steve, by assuming that the only problem area potentially affecting cylinder head cooling, is that of air still trapped in the upper reaches of the cylinder head itself - after correctly bleeding using the bleed tube, that is.

In my point 3.) I had asked whether peeps thought there could be sufficient air still trapped anywhere in the system, capable of critically restricting total coolant flow through the head - or of circulating to where it could do so? If there is not, as you seem to say (ignore heaters, which are not in the main engine cooling circuit, and are not themselves at risk even if they do contain some air), then at that stage, Mazda's high revving bleed/de-gas stages (bleed hose re-bunged), followed by normal running and an eye on the ex tank level for a day or two, is surely all that's needed - no need for a bleed valve on top of the head or whatever?

Don't actual head failures in WL-Ts (as opposed to short term post-bleed hot spots) normally follow a hose failure, or other catastrophic loss of coolant, quickly reducing levels to the point where coolant does not flow through the rad (and therefore the head), then causing rapid thermal runaway at the head unless the engine is immediately switched off? No device added to improve the removal of cylinder head air trapped during re-filling, would save that situation.

EDIT: (If a refill bleed is not done properly, head failures may, of course, occur without being caused by a hose or other ancillary failure first.)

In other words, I wouldn't have thought there is a problem needing a modification to the system to improve head bleeding. It's still all about maintaining hoses, pipes, thermostat and coolant and, after that, bleeding carefully, following any loss of coolant and a refill. Or have I missed something?

Adding bleed points to the heater matrices might be useful if heaters do usually fail to clear air on refilling the system - but again, they surely don't if the Mazda bleed procedures are carefully followed?

[widdowson2008]

Hi Ron
Mazda bleed process is fine - no problems with it at all. What I'm trying to do is remove, IN TOTALITY, the air trapped in the head at coolant change (pre bleeding). This will cut out the initial high revving sequence.
Essentialy, what I am proposing is to introduce into the top hose one of Haydns in line sensor fittings (£10 including sensor).
By removing this sensor during the filling stage, the hole is just above the highest point on the roof of the head (internally). This means that any air trapped in the head will come out here. When you see coolant, the head is 100% air free. Stick sensor back and continue with normal bleeding procedure.
Bonuses are
1 - You now have a sensor in a position reading the true head coolant temperature
2 - You have cut out the need for SOME of the 2500rpm's (always thought this was a bit brutal)
3 - You haven't disturbed the neighbours

I know bongonads (not a complete prat by any means) came up with this originally (using the existing Mazda sensor) but that sensor is a swine to get out/put back without breaking it. This one's easy.

[Ron Miel]

Gotcha Steve! Teased it out of you eventually! Not familiar with Haydn's in-line sensor but it sounds a good idea - for the WL-T, anyway. Perhaps a few peeps trying it first before a sales push by Haydn, would be a good idea. Presumably, my musings about the potential for bigger amounts of trapped air elsewhere, if not bled properly, still hold good? Didn't see bongonads deleted stuff here before it was no more but have been PM-ing with mikexgough on the subject and agree, both of them are on the ball. It just needed more careful cut up and see treatment as well - and you done good, dincha?

EDIT: I suggest that your sensor-bleed might cut out all the high revving (and yes, that is a nuisance to neighbours) but only testing will prove that - how about heater-trapped air, etc.?

[widdowson2008]

Gotcha Steve! Teased it out of you eventually! EDIT: I suggest that your sensor-bleed might cut out all the high revving (and yes, that is a nuisance to neighbours) but only testing will prove that - how about heater-trapped air, etc.?

Gonna put a pic up soon - very rough - cobbled together from different sources - but I think it may give you an idea of where my brain is at.

Agree - needs testing, so I was going to ask Ady if he would help me out. Why Ady? He has bled my Bongo before, made a good job, and I trust him.
What I was thinking of was:
1 - Carefully remove into a container a large volume of coolant.
2 - Fit the unit
3 - See how much coolant I can get back into the system.
any residue would represent trapped air. (heaters?)
If things don't go according to plan A, then it can be bled as normal and the idea put in the bin.
Upside is that I'll have a sensor unit.