Bongo Fury

Bleeding experts required for this please.

i am trying to bleed system (i have done this many, many times !) however, this time, I cannot get the car up to the temp when the thermostat opens !!

What does happen when i try to do this is that lots of coolant comes through the bleed pipe (into my bleed plastic bottle, held higher than the expansion tank) and i have to keep topping up the expansion tank. The more i rev up the more i have in the bottle - what causes this? Is there an air lock stopping the circulation? when i stop the engine it does bleed back but after about 5 mins.
Should i keep the bleed pipe blocked until the engine heats up beyond 85degC then try again?

Are all the heater controls set to hot front and rear to ensure the system is fully open ?

Coolant will come out of the pipe when you rev the engine as the pump will be turning faster and the pressure will be greater.

M 80NGO wrote:Are all the heater controls set to hot front and rear to ensure the system is fully open ?

Coolant will come out of the pipe when you rev the engine as the pump will be turning faster and the pressure will be greater.

Heater controls do not control coolant flow they just control airflow over the heater matrixes, you can turn them on to check if there's heat in the heaters to see if there's airlocks/blockages, but they'll make no difference to your overflowing issue.
Until the stat opens, when the engine is revved, the level in the bleed pipe should drop when the engine is revved.
It sounds like what happens when you get to the point when the stat opens fully, shutting in the recirc/bypass port in the top of the stat, I'd check to see if the stat is jammed open or you've got another blockage, either rad or matrixes top suspects IMO.
Is the bottom hose from the rad getting warm/hot to show the stat is opening at all? are fans kicking in? Why are you having to bleed it? Fulll story may help diagnosis. Worst case scenario, head/gasket issues?

missfixit70 wrote:

M 80NGO wrote:Are all the heater controls set to hot front and rear to ensure the system is fully open ?

Coolant will come out of the pipe when you rev the engine as the pump will be turning faster and the pressure will be greater.

Until the stat opens, when the engine is revved, the level in the bleed pipe should drop when the engine is revved.

Are you sure Kirsty, the bleed pipe is on the positive side of the pump so the level should rise with revs or have I missed something?

dont know what method you are using to bleed your bongo but, did you start by filling the rad, cap it off, then filling the epansion tank,bleed pipe open,and raised.(all done with the engine not running).then start the engine.
the only way i can think of it pushing coolant out of the bleed pipe if its raised above the expansion tank height,is if there is a major airlock,or major blockage.with the stat closed(bottom hose cold)the more you rev the engine,the more it pulls coolant back into the bleed pipe,once the stat opens(bottom hose very hot,not just warm)the bleed pipe flow becomes neutral(neither expelling coolant,or sucking it into the system.


3 videos on youtube,titled bleeding a mazda bongo,may help.

Thank you all for your comments

History: coolant in rad and front heater froze - felt slush in rad. Leak in front heater matrix. Repalced it (boy what a palava!) now trying to bleed.
No bubbles at any time so i think the head is ok.

If the thermostat is stuck open I think (?) that i would have seen bubbles as the engine heated up - but maybe not ??

Why does the bleeding tube have a head of coolant? Is this because the thermostat isn't open?

Top and bottom pipes of rad hot but this could be via heat conduction rather than water flow as I had the engine running for about 40mins

Re: action of heater controls (ie no effect on water course) - OF COURSE ! it's obvious really, but you're the first to mention it - thanks missfixit

to me its still a bit unclear whats going on. what i would do is check flows through every bit of the system.remove as many pipes as is necessary,and establish that everything is clear.put in a new gen stat, then refill everything,and fill it carefully,with the bleed pipe open and raised.

just a thought----did you put the front heater pipes on the correct way round.check the flows through the rad to the stat housing,as this may still be frozen (no flow)the water ways are very fine.

If the bottom hose is hot, the stat is opening/open, if that starts getting warm once the engine temp/rad inlet starts warming up, then I'd go with the stat being jammed open, this would not be shown by bubbles in the system. It should not really start getting warm until the stat opens allowing flow through which is 82-85 c at the stat.
The fact that the level rises in the bleed pipe, (as I said above) tells me that the stat is open or ther is some other obstruction, with the recirc/bypass on the top of the stat shut, this seems to force the coolant up the bleed pipe when revved once at/past this point. This is from observation/hands on bleeding of MANY bongos, see the bleed videos on youtube, not the definative method (there isn't one), but it seems to be the one you (& many of us) use.
If the stat is closed, the coolant should "suck down" the bleed pipe when revved.
Worth pressure testing the coolant system, if it got cold enough to freeze the coolant, I'd suspect more damage than just the front matrix.
Valuable lesson in making sure antifreeze concentration/quality is correct.

The Great Pretender wrote:Looks like I missed something then.....

What did you miss Mel?

missfixit70 wrote:

The Great Pretender wrote:Looks like I missed something then.....

What did you miss Mel?

The interaction between pump, bleed pipe and stat housing on the standard system Kirsty.

It's there

Bear with me missfixit70 for I cannot see it either. But I may be a bit thick on this.

"The fact that the level rises in the bleed pipe, (as I said above) tells me that the stat is open" - I would have thought that the thermostat being closed would increase pressure! What causes the high pressure on the bleed pipe - is it just natural system pressure differential that you get in any pump system ie the resistance to water flow-the pressure out of a pump is high than on the inlet. Or is it due to the thermostat being closed ?

" or ther is some other obstruction" - where ?!
"With the recirc/bypass on the top of the stat shut" Forgive my ignorance - do you mean the hole in the diaphagm or is there some other bypass pipe?

[b]"If the stat is closed, the coolant should "suck down" the bleed pipe when revved."[/b] - I have bled my bongo about 8 times now and this has NEVER happened, there has always been a 'head of coolant', are you sure about this?

"Worth pressure testing the coolant system, if it got cold enough to freeze the coolant, I'd suspect more damage than just the front matrix" - perhaps but it would be a leak wouldn't it, not a blockage

Regarding bubbles - all other times i have bled there comes a point when lots of bubbles come out - this has not happened. Weather stat is open or closed, wouldn't they come through? Perhaps they did come though very early and i missed them ???

Finally do you know of a diagram that shows the bongo cooling system.

Sincere thanks for your comments so far.

I stand by everything I've said already, evidence on the 3 bleeding vids on youtube re rising/falling levels - http://www.youtube.com/watch?v=jRAKOSxgbKo
There are no other valve's etc in the cooling system (what hole in what diaphragm?), but there may be a blockage/obstruction in matrixes or rad as these are very fine waterways. Freezing/thawing maybe coulda distorted sumat, or dislodged some crud that's now causing a blockage? maybe clutching at straws, but it doesn't take much to upset the system, & it sounds like sumats wrong, or there's sumat you're missing/not telling us?
I suggested a pressure test to make sure the system is tight, if it's boiling over it COULD be air getting in, eg water pump seals maybe? have you checked the telltales?
When you have bled previously & you reached a point where bubbles have come out, this is where the stat opens, so no, this wouldn't happen if the stat was stuck open or closed (did you check it opens properly at 82-85c in a pan?).
There are loads of threads with the cooling system - http://www.igmaynard.co.uk/bongo/forum/ ... =3&t=35902 - http://www.igmaynard.co.uk/bongo/forum/ ... =3&t=36433 for starters (these may also help you understand what's happening with the bleed pipe levels/ pressures within the system relative to the stat position, it's not as simple as outlet & inlet pressure as it's an interconnected looped system) , there's also a factsheet. If you can't be bothered wading through that lot, worth giving Widdowson2008 a shout, I'm sure he'll furnish you with the necessary.

I suspect some bongo's must be different Dave, i've never felt a hot bottom hose Warm yes, but i suppose the issue of temps are subjective. Have you tried extending the bleed hose with a hose sleeve and running it directly into the expansion tank as the engine warms? Keep an eye on things (level/temps/heat at both heaters etc) Then when the level drops in the expansion tank (stat opening) top up the expansion tank as required, not letting the level drop below "MIN". Once an equilibrium has been attained, (constant heat at the heaters,steady temp gauge,coolant level steady) Leave ticking over for another ten minutes, then replace the expansion cap. Allow to tick over for another ten minutes or so... If the level is still good, take a top up of coolant in a bottle with you and run the bongo round the block a few times, watch that temp gauge! When you get back home, allow the engine to cool for half an hour or so then check the level, (it should have dropped) top up coolant and repeat the engine re-heat procedure, take her for a run with the aforementioned top up coolant precautions, and repeat until the level reaches an equilibrium...sometimes it only needs a few runs to bleed, others can be a pig.