Bongo Fury

miker wrote:To answer a point that seems to be made quite often on this forum and was made early on in this thread, and happy to join the queue at the wall if I'm wrong, but the comment about bottom hose of the rad being cool while top is hot - surely this means the rad is doing its job.ie. cooling the fluid passing through it. That of course assumes the coolant flows from top of rad to bottom.

Welcome to the wall Anyone else want to join us?

miker wrote:To answer a point that seems to be made quite often on this forum and was made early on in this thread, and happy to join the queue at the wall if I'm wrong, but the comment about bottom hose of the rad being cool while top is hot - surely this means the rad is doing its job.ie. cooling the fluid passing through it. That of course assumes the coolant flows from top of rad to bottom.

But there will be no flow through the bottom hose until the stat opens.
I agree that the temperature of the water exiting the rad will be dependant on how well the rad is doing its job, BUT, when we are bleeding the system & the vehicle is stationary, there is no air flow across the rad until the fans kick in (can't remember if they do or not during the bleed process), therefore the rad isn't doing a lot of cooling & the water will exit the rad warm/hot.
When the vehicle is in motion, there is an airflow across the rad, therefore when you come to a stop & check the bottom hose immediately, it will be cool, wait a few minutes & it will start coming through warm.
How much of this function is affected by the function of the bypass system which in turn affects the inlet temp to the rad?
Now retiring to a safe distance

missfixit70 wrote:

miker wrote:Now retiring to a safe distance

For Gods sake DON'T RETIRE
Your opinion is one that I have always trusted and have another look at the subject line - that's what I'm trying to achieve.
Please don't go

widdowson2008 wrote:

missfixit70 wrote:

miker wrote:Now retiring to a safe distance

For Gods sake DON'T RETIRE
Your opinion is one that I have always trusted and have another look at the subject line - that's what I'm trying to achieve.
Please don't go

Relax man - you can't keep a good woman down for long

Well..................OK then



But only if you promise she really will come back

I didn't say leaving - just retiring to a safe distance awaiting any flak
This thread is looking like it may actually start getting the answers without anyone getting too overheated, good input from everyone on this one so far

I think overall there is quite a bit of understanding between forum members as well as the guru's of the Bongo cooling system, it is just there is perhaps is a need for a "how it works" for the not so informed.

The fact sheet on bleeding is "gospel" but some folks need to understand why the various operations in the technique are there and what purpose they serve although some members have variations on the process.

As for the Radiator, I agree totally that it will not flow coolant until the Thermostat opens and obviously the degree of air flow determines it's heat transfer properties and as Dandy pointed out the thermostat is on the return side of the cooling system which is "unconventional".
As other posts including my own have shown the way that these system work and they seem to be more common place these days.

I think that Widdowson's goal of a diagram is good project and I know there have been a couple already but if something can be done with a "how it works for Bongo dummies or whatever" sheet it could have some value.
I for one, have discovered quite a bit from this thread and looking on the interweb and chatting to mates "in the know", and now understand why Mazda decided to fix the temp gauge to "11'oclock". That strategy was okay when the vehicle was new and with longlife 5 year coolant would leave the vehicle cooling system virtually trouble free in it's life with the Japanese system of car ownership.
It is when the vehicles age that the problems occur and since fitting a Mason alarm I see the fluctuations in the Temperature gauge under differing road conditions and now can understand these changes and how the system is controlled progressively via the Thermostat as it gets hot and as the coolant reduces/raises in temperature with air flow through the radiator.

missfixit70 wrote:I didn't say leaving - just retiring to a safe distance awaiting any flak
This thread is looking like it may actually start getting the answers without anyone getting too overheated, good input from everyone on this one so far

Hi Kirsty
sent you a pm for your consideration

How strange, I was just about to say the same thing.

If anyone's still in any doubt about how the stat's fitted, look here http://www.allansvehicleservices.co.uk/32132.html scroll down & you'll see some very useful piccies & descriptions - nice one Allan

that confirms my thinking.......

Here's my thoughts on the workings of the cooling system. I somehow picked up from previous threads that the thermostat "pointy end" faced up the way - now that its been confirmed otherwise I can make sense of whats happening. If this has already been said in previous threads then apologies.

On "conventional" cooling systems with the 'stat at the outlet from the head the cold coolant heats up in the water jackets and convects upwards towards the thermostat. It does't get past the 'stat at this stage but circulates by a bypass system back round to the waterpump and further convects until it is hot enough to open the 'stat. The 'stat valve is opened by the wax contained in the "bulb" of the thermostat expanding through heat and it opens the valve. There's always coolant at either side of the 'stat (assuming no airlocks) - its the heat transfer by convection thats taking place through the coolant which keeps the cycle going.
The hot coolant, at around 90 degrees, then transfers to the radiator and depending whether it is a crossflow or vertical flow type, travels through the radiator which, as the name implies, radates the heat to the atmosphere. Because modern vehicles have the lower tank on the radiator at a position lower than the engine block, the waterpump then lifts the cooled, dense coolant back up into the engine. Then the coolant recircluation cycles starts all over again.

Now for the Bongo system........................

I think it was TGP who said the waterpump is actually "pumping" coolant around the system on the Bongo, I contradicted him.................and he is right! The Bongo system, with the 'stat in the return to the engine setup does rely on the pump “pumping” the coolant around the engine, whereas the “conventional” setup has the pump “lifting” the coolant from the lower radiator tank to the engine block.

Righto……………I think this is what happens.

The cold coolant is warmed by the cylinders, the waterpump assists the heat travel process by taking coolant from the bypass system above the thermostat (the ‘stat is closed at this point but the disc shaped valve (seen in Allans excellent pics mentioned by Kirsty), is open allowing the bypass system to be open. The coolant heats up, convection currents lift the coolant to the highest outlet in the head, to the pipe seen under the driver’s seat and directly forward to the top of the radiator. As the hot coolant mixes with the cold coolant in the radiator its easiest path for heat transfer is to go up to the expansion/auxiliary tank (because heat rises and the radiator coolant isn’t allowed to circulate at this point due to the closed thermostat not allowing circulation). This hot coolant circulates through the expansion/aux. tank and carries on to the heater circuits and ends back in the previously mentioned bypass system above the thermostat. The waterpump then takes the coolant back from the bypass into the engine block. From memory, there are no external coolant hoses on the pump – it just takes coolant from A to B internally.

The coolant in this system, including the block/head/hoses/metal pipes/radiator top tank/heater matrices/turbo cooling system and various metal pipes will be staying at a fairly uniform temperature. Fluctuations will occur (probably as previously mentioned the reason the gauge is damped) but the volume of coolant and expanse of piping does its job in keeping the system at a safe working temperature, just below thermostat opening temperature. There will a few “glitches” when stopped in traffic/hill climbing/hot ambient temperatures when the coolant temperature will be high enough to heat the “bulb” on the ‘stat enough to open the thermostat. And as the coloured diagrams that Mike Gough posted of the Elise/MG system shows, there will be a mix of bypass coolant and some colder coolant allowed to enter the system from the radiator, via the now partially opened thermostat. This would explain the temperature fluctuations recorded on the TM2 gauges.

If the conditions then really demand extra cooling then the ‘stat will fully open, the bypass system will close off by the disc shaped valve and the entire cooling system will constist of the block/head/outlet hose under the driver’s seat/radiator/lower radiator tank/thermostat/expansion, aux.tank/heaters et al until things cool off enough to partially close the ‘stat again and the system reverts back to the former setup. The closed off bypass system then allows the warm coolant from the radiator bottom tank to go past the thermostat directly into the engine block. Allan’s photos show this.

If this the case, then vehicles used in cold climates in Japan or Europe might rarely have the complete system functioning in full flow and possibly why the radiators in these vehicle choke up.

Thanks for reopening this one widdowson, I think it’s becoming clearer through time……………………….and nobody has fallen out …………………..yet!

Dandy
I don't think you are right on the Bongo system, I am 100% sure you are right.
The reason for me saying this is:
I have produced, totally independantly of yourself (apart from cribbing some of the thoughts penned in this posting), a simple schematic of the system in its various stages through a complete cycle.
I have studied the photos from Allans Vehicle Services. I have studied the Mazda pipework drawings posted earlier. I have discarded all the negative crap which this topic (and so many like it) has attracted, I have utilised the positive comments, and stuck to my original plan (see subject of topic).
The result is so close to what you describe - it's uncanny. You were describing my schematic..... and its totally logical.

This has got to be progress surely?

Where to go from here?

Kirsty suggested that I run the diagrams past certain folk to get their constructive opinions, and your name is one that came up.

If you are willing to spare the time, I will email them to you for scrutinisation.

They will not be perfect first time round, but they will when all the constructive info is fed back - believe it.

I am so happy - you would not believe it I've got a schematic that I understand - yipeeeeeeeeeeeeeeee

That makes complete sense to me, nice simple explanation especially the bit about the stat not needing to open on many bongos (resulting in the rad getting choked) as the cooling is being taken care of by the rest of the system. This is something Bob (Freewheeler) & I were discussing earlier in the year, basically saying exactly that. I reckon this also leads to the stat not functioning properly through lack of use, I know of one or two that had basically "welded" themselves shut. How many bongos in the uk are only really doing short runs or just pootling around at low speeds & never actually opening up? Then when they are called upon to do so on a long run, or fully loaded, towing a shed- disaster

From this can we also draw the conclusion that if your bottom hose does not get warm during the bleed process, that you are not getting full flow through the rad to the stat & therefore not bleeding it properly, chances are it'll be a stuck stat & maybe a blocked rad, either way, a cold bottom hose is a problem that needs sorting IMO.

It looks like someone's going to have to factsheet this lot before it all gets lost/pruned/forgotten

Keep it coming Looks like we may finally reach agreement on this one