Bongo Fury

Right, thats that sorted then Just getting my head around the cooling system Franco

Ok vanmanerik, have you thought about how the themostat when mounted on the way out of the cylinder head increases the pressure in the head, so better cooling the hottest part of the engine (around the exhaust valves)?

I haven't seen a Bongo 'stat yet but looking a photo, can someone tell me what circuit the lower valve blocks off when the stat opens?

Bypass Dandy?

That's what I was thinking too but it looks like it closes off the hose to the radiator bottom in the exploded diagram

Hi Dandy

The thermostat is in-fact the other way up from the pic. As the thermostat opens to permit the flow from the radiator to cool the system, it closes off the bypass (the pipe running from the head, to the thermostat; behind the alternator).

We think that it is likely that the thermostat is constantly opening and closing to maintain a constant coolant temperature, according to driving conditions (up hill, down hill, speed, load in vehicle, etc.).

We think this results in a steady minor flow though the radiator that results in the lower pipe being cool to warm but not hot, as the radiator is very large and efficient, as it is designed for a hotter climate.

Thanks Dannyboy - you willing to discect your old rad as mentioned in the schematics thread??????????

Hi Dandy

We will have a look at it later in the week, but after pouring water through the old and new ones we don't think that there are any sensors or valves inside.

A minor, random input from me. I was thinking about the little hole in the thermostat, which seems to have a simple gravity type valve (little ball on a stick!) device in it. I know it was mentioned earlier tat it was for allowing trapped air through, but there is another possibility. Could this be intended to allow a small flow of water so that whatever temperature the water is reaching as it warms up after engine start, that temperature is experienced all round the thermostat (not just on the 'upstream' side) so it can respond in a smoother more predictable fashion. If the flow is sluggish due to a blocked rad, then it might explain why drilling 3 holes helps to achieve the desired result in allowing the thermostat to sense the rising temperature, open as it should, and prevent a boil up.

Cant really think what the little valve is for unless to stop blow bakc of cold water coming (for some reason I cant fathom) from the far side of the thermostat.

Any thoughts?

It won't Mike - the "jiggle pin" is there to allow air past but whenever coolant gets to it it closes as the "ball" part of it floats. It's only purpose IMO is to be used in the filling process and allow coolant past and air out of the system

So Dannyboy, if the system is made for hotter countries and can cope with anything we can through at it in the uk, why the head problems?
If the hottest part of the engine is where the problem is, its down to a cooling problem, and size here aint important, design is.

Hi mikeonb4c

We think that the little toggle valve is there just to let the air up and out of the bottom hose when filling etc, as as soon a flow of water goes up it closes off the valve.

if you squeeze any of the main cooling pipes when the engine is off you can hear the toggle valve close.

We assume that as the water pump is constantly pulling the water through the system it would be impossible for the flow to pass down past the valve to the lower pipe.

The Great Pretender wrote:So Dannyboy, if the system is made for hotter countries and can cope with anything we can through at it in the uk, why the head problems?
If the hottest part of the engine is where the problem is, its down to a cooling problem, and size here aint important, design is.

Well there is indeed a problem, but... the comment was more to explain why the flow from the bottom pipe was cool, not hot, rather than the system working correctly. As we have now in the last 4 weeks (perhaps) changed/ switched the {thermostat (old, new, holly with different number of holes) and radiator}, bled the system 12 or so times, with only 3 occasions when the bottom hose warmed up with the new stat in place, as suggested in the manual, on these occasions, the bongo is stationary and the fans are off. As soon as the fans come on or the vehicle starts to move the flow of air through the radiator cools the water to enough of an extent that the lower hose is cool.

Hope that makes some sense, though looking back over all that I'm not so sure.

Dannyboy, think you have resolved your problem to a certain extent..........the water isnt going through the rad the stat is bypassing it. But putting the stat anywhere but on the return from the head to rad is a no-no

Exactly, The Great Pretender.

For some reason though we don't know what, the flow from the rad to the block is not working, without holes (as of this evening 4 holes; not 5 or 8 or 1) in the stat.

And in-order for the bypass circuit to be closed the stat has to be where it is.