Bongo Fury

Or there is the argument that a completely drained system could have been filled up from scratch, the coolant just glugged in (thus introducing a lot of air initially) Then a rather large airlock in or around the stat housing... One side of the housing having hot coolant, the other "side" having cold coolant. Now i know the stat (regardless of whether it being a spurious or genuine mazda stat) Doesn't open at the rate of a swung open front door It opens gradually, swirling the hot and cold coolant together, the stat (via the internal wax of the stat which dictates how much it opens or closes) then senses the combined hot and cold coolants mixing together, and adjusts it's opening/closing rate to suit. I suggest that if the bottom hose gets suddenly much warmer, then an airlock has moved as the stat opens, and suddenly the hot water side has heated the bottom hose also.

The stat only has to open a little for the flow through the Rad and bottom hose to take effect....it is being pumped and is under a fair bit of pressure once it reaches 82C....it is not the coolant in the bottom hose that causes the Stat to open, it is the coolant in the bypass system....heaters/ex tank/red top tank....cylinder head flowing above the Stat that opens it..

If you hold the bottom hose....it goes from Cold to Hot very quickly

haydn callow wrote:
If you hold the bottom hose....it goes from Cold to Hot very quickly

In every single case? Or just with your experience? Like i've said elsewhere, i, personally have never experienced that to occur But it could just be me!

bigdaddycain wrote:

haydn callow wrote:
If you hold the bottom hose....it goes from Cold to Hot very quickly

In every single case? Or just with your experience? Like i've said elsewhere, i, personally have never experienced that to occur But it could just be me!

I suppose I have bled around 40 bongos to date and with experience I know roughly when the Stat is about to open...at that point I hold the Bottom hose....it goes from Stone clold (engine been running for about 30 mins at this point) to luke warm for about a min then too hot to hold in another min or so.......it really is a very positive rise and once you carn';t hold it you know the stat is open and the bleeding (vidio way) is just about complete.

I belive you bleed a differant way so perhaps you don't get the stat open....Thats fine and you can get all the air out of the system except perhaps a small amount trapped in the Bottom hose....this would explain why you normally have to have a small top up for a day or so.....I have never found that needed..

Oh the stat definitley opens when i bleed a bongo Haydn, as the coolant level drops in the expansion tank when it does open! Perhaps i've been too busy keeping an equilibrium of coolant level as the stat opens to check the temperature of the bottom hose,as you know there is a fair bit to do with just two hands with all this bleeding malarkey! I'll make a note to check the temp of the hose next time, i've probably simply not checked the temp as much as yourself.


I've heard of the youtube video, but never seen it, as i use a slightly different bleeding technique.

Perhaps i should give the other method a try... I've always (and still are) of the opinion that a bongo cannot be 100% bled "on the spot" as it were, as there is always a follow up top up required after the bongo has completely cooled. In fact, i've heard of quite a few bongo's down the years that have employed the same bleeding technique as yourself and have still required a top up following a cooldown. Perhaps they didn't get the stat open either, and not followed the bleeding technique 100% perfectly.

Sorry, i forgot to mention, i've only bled around 20 or so bongo's thus far,so you are twice as experienced as myself!

mike-- i have been experimenting with the standard bongo temp gauge,after finding a fault on a friends gauge,which i also had,this made my mason whistle occasionally,this was traced to an electrical anomally,which was a low voltage being sent down the wire from the gauge to the sender,as the sender works on low voltage this registers on the gauge as a reading.i had to remove the mason in the end as the mason is very sensitive to voltage fluctuations and redo the gauge diodes.this inturn points me to the voltage stabilizer which smooths the voltage to 12 volts for a steady reading on the gauge regardless of engine revs.
the mason works well in my wifes bongo where there are no problems with the electrics,and is a cracking piece of kit.

on the airlock front,the more i bleed bongos the more conviced that any airlocks present whilst bleeding,are not to be found around the stat housing,the jiggle pin allows any trapped air to be pushed through the stat,all be it slowly,in my opinion they are to be found in the front heater,rear heater,head,but mostly trapped in the top hose outlet from the head where it dives down to the rad.whilst the engine is stopped and there is no flow the pin drops and opens the little hole,(self venting) the hole is positioned in the highest point on the stat. but when the flow increases whilst the pump is running the jiggle pin closes the hole.the trapped air in the top hose always tries to rise so this air goes backwards up to the head when the engine is not running.

WOW that was an interesting read to my initial post

Will keep a very close eye on temps, Thanks for your comments

mikeonb4c wrote:Haven't read through NB's post but my temp gauge starts to move of from the Cold stop after about 5 mins driving. I take this as a clear indication that the stat has opened and circulating/warming coolant is starting to flow past the temp sensor. Before I put a new thermostat in, it used to take twice as long for this to happen (which is why I feel confident in linking this event to the stat opening).

Turn your thinking around Mike, if your old stat wasn't closing fully or was blocking the bypass it would take longer to warm up than a closed stat.

haydn callow wrote:
What happens is !!!! The standard Bongo temp gauge is activated by a sensor which is located in the cylinder head......When the coolant in the cylinder head reaches 25C the gauge starts to move....when the coolant in the cylinder reaches 45C the gauge will be at it's "normal" 11 o'clock position.......it will then sit at that position untill the coolant in the cylinder head reaches "approx" 110C.....and you are on the cusp of a overheating event.....

Whatever you used to get those figures needs checking. As you know I had a thermistor in direct contact with the coolant located in the top hose, the temp was in the high 60's before any movement then quickly reached 11 o clock.

Hi
Mike
Regarding the chocolate fireguard...I believe , as is common in the English language, that there are two meanings to the word Guard...one being a physical barrier such as a machine guard, or a mesh screen, the other meaning being an act of minding, or watching, in fact...a sentinel....thus we confuse the chocolate fireguard of inventor Jedediah Tribble...Much like an hour glass with an elongated tube between two glass bulbs, it is placed near a boiler system, and if the solid chocolate in the bulb placed at the top melts and runs into the lower chamber, then it is time to damp the boiler. The chocolate can be cooled and re-used, and as with an egg-timer, just turned upside down
The Mazda gauge is perfectly O.K. It is not fitted for no reason...car manufacturers don't do that. It is just heavily damped. The Bongo is for the Japanese market...If the gauge moves, then the Japanese owner stops and finds out why, and calls the rescue services. Thus the gauge works in Japan. Now...enter the European owner...often Male, and they are the ones that buy a new product, and before they open the box at home and read the instructions, they know exactly what they are doing ...and when it doesn't work, the lady of the house reads the instructions and gets it going... ( I have one like that at home ). Right...when the temperature gauge moves, the European way is to drive home slowly and hope nothing happens....mmmmm....NOT what Mazda intended!
My personal preference is for a gauge that moves up and down according to the conditions...I still keep referring to the original, and who knows, it might pick up something the other gauges don't
Cheers
Helen

The Great Pretender wrote:

haydn callow wrote:
What happens is !!!! The standard Bongo temp gauge is activated by a sensor which is located in the cylinder head......When the coolant in the cylinder head reaches 25C the gauge starts to move....when the coolant in the cylinder reaches 45C the gauge will be at it's "normal" 11 o'clock position.......it will then sit at that position untill the coolant in the cylinder head reaches "approx" 110C.....and you are on the cusp of a overheating event.....

Whatever you used to get those figures needs checking. As you know I had a thermistor in direct contact with the coolant located in the top hose, the temp was in the high 60's before any movement then quickly reached 11 o clock.

Hi...I also have a temp sensor located inside the top hose...and a few elsewhere....my readings are much the same on all 3 Bongos I have owned........I am confidant the readings are good but I will recheck next time we go out.

The Great Pretender wrote:

mikeonb4c wrote:Haven't read through NB's post but my temp gauge starts to move of from the Cold stop after about 5 mins driving. I take this as a clear indication that the stat has opened and circulating/warming coolant is starting to flow past the temp sensor. Before I put a new thermostat in, it used to take twice as long for this to happen (which is why I feel confident in linking this event to the stat opening).

Turn your thinking around Mike, if your old stat wasn't closing fully or was blocking the bypass it would take longer to warm up than a closed stat.

Thanks Mel - now that's the kind of answer that gets my attention (though I hope you've bled a sufficient number of Bongos to be qualified to give it ). I'm still puzzled by what seems like a v. positive lift-off of the temp gauge needle from the C stop (and that time to do that halved when I fitted a new stat), as I imagine this as being linked to a rapid rise in temp of coolant passing the sensor, such as might happen when something had opened, allowing hot coolant from somewhere to flow past the sensor.

Anyway, I musn't waste any more of people's time with my endless questioning. If I can find the energy, I must go off and do some head-scratching about what (if any) link there is. But it does seem that the behaviour of the (standard) temp gauge reflects the performance of the thermostat (and never mind the sceptics), and so may have some value as a diagnostic tool.

Like Helen, I'm not one of those quick to dismiss the standard temp gauge as no more use than a chocolate fireguard: in some respects I wonder if it is better than an undamped gauge. As an example (taken again from gliding), pilots use a device called an 'averager' to tell them what the real strength of a thermal (current of rising air) is, as it is much harder to make an accurate assessment on whether the thermal is worth staying in (in order to gain height) based on the constant fluctuations in thermal strength as indicated by the standard undamped instrument (variometer).

To the original topic poster: apologies, anything that gets near to a question about the Bongo cooling system is well known for setting off a heated debate (no pun intended, yea right ha ha )

This is an excellent thread for any newbie on the forum! As it's varied in it's nature, yet maintaining the overall subject matter, thus covering a few aspects of one particular issue.

It's brilliant that the whole coolant debate (for want of a better term) is now taken seriously (sometimes a little too seriously) when i'm in the correct state of mind i "contribute" what i can here and there on the subject. I'm no expert, have no mechanical background, but i have been told i'm quite sympathetic with anything mechanical. I'm also the type of fella that you won't see arguing unless i'm pretty sure i'm correct! (that's why i don't lose many arguments)

So let's get this whole subject into perspective... I have (as have others) Carried out a bit of research in Japan to see if they too have issues regarding our beloved bongo's overheating... (the biggest barrier in easily attaining info is the language barrier) Computer based translations just don't cut it The japanese appear not to have an issue with bongo's overheating... EXCEPT, if work has been carried out on the cooling sytem and the follow up bleed is problematic. I maintain, (as i have said previously) A fair share of problems with UK based bongo's can be attributed to the wrong type of coolant being added to the original japanese coolant with dire consequences. Until recently this has mainly been overlooked. Of course, another issue is that old,tired hoses have passed their prime, fail, then perhaps minor undetected damage has occured which would eventually lead to a major failiure (usually the cylinder head). Thankfully, no matter what bleeding technique is employed over here, the bongo has a back up self venting feature that often saves our bacon. The self venting isn't always adequate to remove all the air quickly enough, hence our efforts to intervine with our own bleeding. Bottom line? If the majority of the air is shifted, the bongo does the rest in a healthy system (yeah i said it!) Now you can debate this with me as much as you like, but the fact remains that's just how it is!

We can argue the toss over the subtle nuances of the finer points of bleeding till the cows come home, the main thing is, we know we need to bleed,we know we have to be vigilant, we know to respect the system, if we look after it...it'll look after us!

Can i just add my 2 pence worth for what its worth i bleed my bongo simply through bleed pipe into a demi john lock the bleed pipe off ( home made locking bleed pipe) top up with antifreeze keep repeting untill air has gone this method worked for me when changing my rad and water pump, i had no problems with air locks,,, i dont know the right way or wrong way to bleed a bongo i just know that this way worked for me! jus my opinion