Bongo Fury

Have you radflushed the system? I would give the system a thorough flush, new coolant and bleed the system. I do not undersatand drilling holes in the thermostat, surely ifyou have fit a new thermostat and the system is clear the thermostat would operate within the temperature tolerances, I would make sure you are getting a good flow through the radiator, if not perhaps a new radiator is needed.

I don't think it is likely to be the radiator..... as the the radiator is part of the post-thermostat circuit....and without the thermostat it runs cool...I still go for a restriction or blockage that is stopping or slowing the water from going past the top of the thermostat....you really need to test that or try and clear that out...

If the temperature is less than 82 degrees it will not open.... despite the fact that the head is overheating.....

I understand how confusing this it... as the simplistic two circuit model i illustrated was to demonstrate .... the heater circuit also runs as a parallel circuit of the pre-thermostat warm up circuit...so now we have three circuits !!

The system i speak of is the same in virtually all cars and is fairly logical if you put your mind to it....

If the water was not flowing past the "stat" then it would be queuing... and therefore with no flow the water would remain cold at the stat.....moving water increases in temperature as it goes round the block and through the minor cooling circuit......past the stat and back round the block - when the temp of the water gets to 82 degrees the stat opens and the water has free flow through the main cooling system and radiator... We know that there is a good feed to the stat as the flow is sufficient when it is open to succesfully cool the engine...so the blockage is in the return after it passes the top of the stat...

I used to be a RAC / AA approved roadside contractor in a previous vocation.... i repair and unlock mobile phones now !

Duncan

I would advise listening this this man (mobyfix). It could explain other mysterious episodes. Hearing this talk, I have a dim memory of having to deal with a similar mystery on a car of mine30+ yrs ago. As mobyfix says, its very simple when you think about it. BUT the circuits will need testing somehow. Any practical tips mobyfix? This is an interesting thread.

As with most Roadside Technicians... I am a diagnostic mechanic....good at fault finding and lazy to do real work on cars !! I can using logic work out the nature of the problem but as to curing it.....lol. If I can't do the job in 20 minutes at the side of the road, i would refer it to a garage and go to my next job... So in this circumstance i would have done a temporary bodge of removing the thermostat and sending them on their way with the recomendation of having a permanent repair done at a garage. Our job was to keep them going but with a relatively low turnaround time allocated to each job. The RAC or AA pay for a callout ( about £30 - £40 ) and milage if it recovered more than 20 miles, but they don't often pay for extended roadside repair work.

Seriously though, being relatively new to Bongo Ownership I am unfamiliar with this engine and would want to see a cooling schematic to work out where the restriction is likely to be ( in a pipe, hose or through the block ). When you know where it is you will have a better idea of how to shift it..... we are now talking about plumbing !!!

Duncan

Hi Mobyfix, I understand and agree with you about dual water circuits, we used to call the secondary circuit the 'bypass', it allows the water to circulate past the thermostat in a 'small way' untill the water temp is high enough to open the thermostat when of course you will have a full flow of circulating water through the engine.

I too would like to see a cooling schematic for the Bongo as it appears to be a very strange setup.

In a 'normal' engine the heated water flows out from the top of the engine, usually the cylinderer head through the thermostat to the top of the radiator, the water is cooled and then passes out through the bottom hose to return to bottom of the engine block to complete the circuit, the whole sytem being driven by a water pump somewhere in the circuit.

Now if you go and lift the driver and passenger seats and the bonnet of your bongo you will be able to follow the Bongos water circuit.
From under the drivers seat see the hot outlet pipe from near the top of the engine going to the top of the radiator, look under bonnet and see hot water pipe goes to top of radiator, now see bottom water pipe going to the engine, now look under passenger seat and the cold water pipe goes to the THERMOSTAT ???? before returning to the engine.

So whats that all about - a thermostat on the cold return pipe??
I have never seen that before. So in my opinion the whole engine block has to get very hot right to the very bottom to actually open the thermostat so the top of the block and the cylinder head will be screaming hot. No wonder the Bongo is well known for overheating.

Perhaps one of our rich members with the £60.00 service manual could check this out for us please?

No doubt you will let me know if I am wrong on this obsevation.

I think (though I havent traced the pipes carefully) that the hot water from the engine block must enter through the bottom hose, which is why the bleeding instructions (not trying to be rude ) say check the bottom hose to see if it is hot (i.e. water is returning OK from the block). This would fit with the position of the thermostat and with your point about it being on the return circuit Vanmanerik. No doubt the BF cavalry will be along to qualify/correct the above shortly

Right.....now we're on the trail - I didn't realise the thermostat was on the RETURN side.....good call vanmaneric!

This is common practice on VW/Audi and others and the only reason I can see for it is to allow the 'stat to open at a lower temperature and therefore be more reliable.
I should have sussed something was strange when you mentioned the 'stat was an 82 deg. one

Choked radiator HAS to be the problem then Dannyboy.......the coolant can't get to the 'stat in sufficient quantities to heat it to open it.........drilling holes in it allow some flow.

Oh, and vanmaneric......the water pump only assists the coolant to lift it up to the engine block from the radiator lower tank - then convection current flow takes over and the hot coolant rises to the radiator top.

Golden Oldies might remember the thermo-syphom systems of cars with huge high mounted radiators - no pump required as the radiator was higher than the engine......

Vanmanerik wrote: Perhaps one of our rich members with the £60.00 service manual could check this out for us please?

Well, don't expect it to tell you anything very useful (certainly no diagram of the cooling system is included) and it doesn't seem to mention the interior heaters that I can see.

Anyway the only clue is the diagram of how to fit the thermostat where the connecting hose is labelled "Upper radiator hose 2". Is this any good to anyone?

It certainly sounds like it would be worth trying to draw a schematic of the cooling system out of this discussion. I think those that can understand it (ie not me!) should have enough data.

alphabetter wrote:Anyway the only clue is the diagram of how to fit the thermostat where the connecting hose is labelled "Upper radiator hose 2". Is this any good to anyone?

This gets even more confusing - I guess the manual is wrong as it appears that it's the bottom hose that goes to the thermostat.

francophile1947 wrote:

alphabetter wrote:Anyway the only clue is the diagram of how to fit the thermostat where the connecting hose is labelled "Upper radiator hose 2". Is this any good to anyone?

This gets even more confusing - I guess the manual is wrong as it appears that it's the bottom hose that goes to the thermostat.

I thought you might say that. However I have just thought of another explanation. It could be "hose 2" on the "upper radiator", not the "upper hose 2" on the "radiator".

So my guess is that the main radiator is the "upper radiator" and the small one in the engine bay is the "lower radiator" and that this is "hose 2" going to the main rad!!!!

Can anyone scan a diagram of this??

To avoid any copyright problems here is my simplified version of the diagram in the manual along with how I think it connects to the radiator based on the description here.

Thats all I need to see thanks alpha.......and thanks for avoiding copywrite issues.

If the radiator is partially/fully chocked then the thermostat cannot open as there is no coolant circulation to operate it. It might get hot at the top but the waxstat capsule must be imersed in coolant at 82+ deg.

So radflush may help in that case

It might do Pete but if it's so bad I'd bite the bullet and fit a new radiator - as you know only too well, overheating can cause endless troubles, especially if the radflush only relocates the sludge.