Bongo Fury

Sorry dannyboy for coming into this thread a little late, so apologies if I go over old ground. Firstly, the idea of the expansion tank is so that when hot, the coolant under pressure expands and it needs somewhere to go and therefore the expansion tank. So after a run when the engine is hot you would expect the level to be high in the expansion tank. That's why there is a max mark. If you fill it higher than the mark when cold then there is a likelihood of it overflowing when hot.

Now your overheating problem. Are you losing coolant when the engine overheats? What happens when it cools down? What should happen is that on cooling down, the excess coolant forced into the expansion tank when hot is pulled back under vacuum. If you find that the level is down in the rad but high in the expansion tank then you are losing vacuum so that the coolant isn't drawn back and air entering the system is. This can be due to a faulty rad cap or leak in the system (which could also mean a HG). But before panicking and expecting the worst you need to know if you are getting a leak from a hose. A small pin hole leak can cause coolant to come out under high temp and pressure as steam but when cold all seems well. So first thing to look for are any tell-tale signs of coolant anywhere, including white/blue evaporation marks on any components especially around hose connections. If still no joy then try pressurising the cooling system (when cold). I've not tried this on the Bongo but you may be able to use a foot pump to pressurise the system by pumping air through the expansion bottle overflow. Failing that, temporarily replace the pipe from the rad to expansion bottle with a small hose and attach a pump to it. You only need about 10 psi or so, then whilst under pressure take another look around for small leaks. Best if you can do this when the van is stood on dry ground. Of course I don't have to mention about hot components and not removing rad caps when hot.

I know this sounds silly but I remember years ago (when I was a lad fags were 5 for 1d ) a mate who used to take a radiator off the car, lay it flat so the inlet and outlet pipes were pointing upwards, make sure the rad cap is on and now the bit you have all been waiting for - fill it with coca-cola and leave it for a day, all the crud was softened and came away with a hose pipe water flush through.

I can believe that. It's recommended to drink coke following watersports in rivers and lakes to kill any ingested bacteria (and to think that people pay good money to rot their digestive system with this stuff!).

Really excellent stuff here DannyBoy. I'd positive enjoy working through Veg_Ians checklist. Cheap and v. educational and may well be where the problem lies. And the Coca-Cola thing sounds highly plausible. I wonder what radflush would achieve and how long it could be left in to do its job before draining it off along with dissolved crud (mind you after carrying out Veg_Ians checks you might have it sorted anyway).

Good luck m'boy, good luck

what a absolute bummer dannyboy, iv just ordered a new rad as well will be here this afternoon i might as well leave the holey thermostate in iv got a long run down to somerset tomorrow so cant risk it overheating, mines still running spot on with the holey thermostate temp at 1030, ill see if it changes with the new rad, ill let you know

Now then!! just got back from Allans Vehicle Services in Plymouth. I went down co's a month ago when he checked over Bongo for me, his hawkeye spotted that my tophose was bulging a bit and could do with replacing. That what I've been down there to get done today.
Firstly, after driving down there (100 miles @ 60/70mph) my bottom hose was only slightly warm to the touch (stat not opened) Top hose was Very Hot and the expansion tank Hot and the two small hoses that go to this tank also very hot.
EDITED to prevent confusing information on forum.

im a little confused with the fact that a holey thermostat keeps the engine cool i know thats its being cooled by the radiator (as i thought all cars would) but surley if there were leaks in or out you would still lose coolant or get trapped air with a holey thermostat?? plus how does the bongo lose 60% of its heat through a red hot exhuast i hope someone can explain this. also on the thermostat theres a little hole anyway but does this close or allow water through??? maybe adding holes is just helping it along??????

Thats why the exaust is red hot. Co's it's taking heat away from the engine. The rad does not do any cooling on a Bongo under normal conditions, only when well stressed on a hot day ( and even then perhaps not)

yeah i understand the heat lost through combustion, but water temp being cooled through the exhaust? its beyond me

Hi Jamesnjane
The heat from the coolant isn't lost through the exhaust. 60% of the heat generated by the engine is lost through the exhaust, the remaining 40% is dealt with by the cooling system.

oh sweet

The heat generated by the combustion of gases is what causes the engine to get hot. It would seem that about 60% of this heat goes out as hot gas down the exaust, whats left is cooled by the engine cooling system. In the case of the bongo diesel most of this is removed by the coolant bypass system/fans/airflow. Only in extream conditions does the engine coolant at the stat reach the required 82oC to open the stat and pump coolant through the rad. This is why the bottom hose normally stays cool to the touch. Hope that makes sense if not perhaps on of the guru's would like to step in.

I have bled my bongo. I do not over rev the engine and use a funnel and the see-saw method
just seems a logical way to do it, I also squeeze all the hoses to disslodge the trapped air

There's something very odd about this. OK so the Bongo (and presumably most cars) lose 60% or so through the exhaust. So it is the other 40% we are interested in. OK so the Bongo loses a lot of heat without resorting to the radiator (sounds remarkable but I suppose I'll have to go with that). But I cannot buy the idea that the expansion tank is an essential part of the cooling system - that sounds downright weird. There it is, made of plastic, intended to take up the volume caused by expansion and contraction of water with temperature. It is plastic (I know plastics can handle heat, but they are not good heat dissipaters), has no cooling fins (or anything else) to maximise surface area to volume ratio. I haven't looked, but I'm astonished to find the pipes to it run to and fro from the cylinder block. Sounds like the expansion tank is about to practice constructive dismissal on the radiator.

And then there is this. If the thermostat only opens occasionally, when the engine is really heat stressed, what is it that causes my temp gauge to stay on the cold stop for 5 mins then visibly kick off and move up to 11.00 o'clock. I had always assumed it was a classic thermostat opening symptom but I now need another explanation

Yrs

Mike O'Confused (well I am that anyway, but I'm plumbing new depths here)

I tend to agree with you mike, seems a odd system to cool the bongo, I believe the thermostat takes a more active role.