overheat while stationary, thermostat?

[scanner]

You also talk about movement of the temp gauge needle, but this is notoriously inaccurate unless it's been modified with a "Mason" alarm.
Un-modified it supposedly only rises above 11o'clock AFTER water temp has risen dangerously high.

Have you got a Mason alarm fitted? If not needle movement really isn't much guide to actual temperature change.

[nigelginny]

No i didnt re bleed the system? is it that delicate? i say five litres but more likely it was about three, how much coolant would you have to lose before it was necessary to bleed the system? my wife drove over 3 hundred miles after i had topped up, not all in one go but over the week, would an airlock stay in the system for such a long time without showing signs of overheating? i have no alarm fitted but once this is sorted i am going to invest in haydn's alarm.

[mikeonb4c]

Its all guesswork here but, bleeding aside, there is still the significance of the rusty coloured coolant to consider. I know the expert view on here is that it is disturbed by the boiling episode but what I'd like to know is whether a healthy system (one that had regularly had it's corrosion inhibiting anti-freeze changed) would even have any rusty sludge deposit to disturb. Provided you have the enthusiasm for it, I think removing the radiator and backflushing it (do you need to remove it to backflush it effectively though?) is a good idea. Somewhere on BF (Have a search) is advice on testing the flow rate, based on pouring a known amount of water in atthe top and seeing how quickly it comes out the bottom. It would be interesting to test that. Even a 'before and after' flushing comparison might tell you how successful you've been in backflushing.

[haydn callow]

Your basic current problem is air in the system...You only need to drain about 1 litre for air to be introduced.. I.e. empty the header tank so the level drops below the in/out pipes. The rusty coolant is caused by boiling the coolant and stirring the crud up...As you now have to bleed properly (if you are unsure ...find out.) IT MUST BE DONE PROPERLY...I would advise flushing out the whole system and backflush the rad...When all is clean then refill with fresh coolant and bleed. Do not drive the Bongo till this is done.
Lets hope no lasting harm has been done.

[haydn callow]

nigelginny...have pm'd you

[Trouble at t'Mill]

Pure speculation on my part here, 'cos I don't know the intricacies of the Bongo cooling system, but now that you mentioned having drained off a few litres and replaced it with coolant, if the level dropped much below the expansion tank pipes - which it almost certainly did -then air would also almost certainly have been drawn into the system.

Is it possible that a small air pocket could be kept in circulation - and therefore not have any detrimental effects - by a higher-revving engine (one that's been driven), but once at idle - with a subsequently lower flow rate in the coolant - it can 'settle' at a point where it starts to cause chaos?

Nigel, you seem prepared to remove the rad and flush through? If so, then give you whole system a darn good clean through - I'm sure your Bongo will thank you for it.

As mentioned above, I've no idea how effective 'flushing' chemicals are, but since there's now a fair chance your rad isn't actually sludged up, then no harm in adding some just to clean out your channels and pipes, etc.

Then remove the rad, back flush - make note of anything that comes out - refit, fit new stat (why not?!), and then replenish with full concentration (50:50) of the correct (!) inhibitor, and bleed your system.

Replace any obviously dodgy looking hoses too, of course.

Very good chance you'll be ok after this, and you'll know your cooling system will be in tip-top condition.

(I did as you when I topped up my inhibitor level - opened the drain plug at the bottom of the rad and topped up with inhib via the exp tank, but I made darn sure the level never dropped anywhere near the pipes. I reckon I added around 3 litres of inhib before it started to come out the rad bottom, so ideal for topping up if your existing coolant is clean and already has a fair bit of inhib in it - as my did.)

[Trouble at t'Mill]

Oops - Haydn got there before me!

[mikeonb4c]

Haydn. Whats your view on whether a healthy system should have crud in it or not? Is an amount of crud an inevitability?

Good advice from TA t'M above there. In your situation, and obviously assuming I was able to handle the financial pain (not guaranteed!), I'd be tempted to fit new bits and alarms so that (hopefully!) I had a reconditioned and efficient system in place. But a good old clean etc. as advised above would make a good 2nd choice for action. Good luck

[scanner]

No i didnt re bleed the system? is it that delicate?

The quick answer is YES as many many threads on here will tell you

i say five litres but more likely it was about three, how much coolant would you have to lose before it was necessary to bleed the system? my wife drove over 3 hundred miles after i had topped up, not all in one go but over the week, would an airlock stay in the system for such a long time without showing signs of overheating?

Easily - If she only did shortish trips that never properly got the system thoroughly warm right through. With all it's hoses and heaters etc. the Bongo cooling system is more complicated than most others and doesn't forgive treatment other systems happily cope with.

i have no alarm fitted but once this is sorted i am going to invest in haydn's alarm.

Haydn's alarm and Dave Mason's alarm are very different creatures that do very different things.

Haydn's warns about low coolant level, whereas the Mason alarm warns of high temperature AND modifies the operation of the gauge so that is more sensitive and more accurate in that it ACTUALLY moves when the temp goes up and not suddenly jumps up AFTER the temp has risen to dangerous levels.

[Aethelric]

Have you checked BOTH fans? (Can someone tell me the difference between them - what each does?!)

One fan has five blades and the other one has seven. The seven blade one is higher power. I have no idea why!!. I believe they always operate together, at low speed, usually when stationary or at high speed, when the engine gets hot due to heavy load and low roadspeed (going up hills).
I know from experience that it is possible for the fans to appear to be OK (you hear them come in), but for at least one to be defective. The entire blade assembly one one of mine had broken off the motor. It was fine around town or stationary but the temperature got dangerously high going up hills.

Dave

[haydn callow]

Mike...I would say that a system properly maintained from day one (coolant flush/change every 24 months) would stay clean..However it seems that this is not the case in Japan and in fact does it happen over here. Once crud settles in the lower recesses it would be very difficult to flush out so it probably takes a overheating event to get it moving..This is the time to flush before it starts to settle again. A badly stained tank is a sure sign that at some time the system has boiled up.

[haydn callow]

concentrate on flushing/cleaning/refilling/bleeding for now....anything else is probably a distraction at this point.
The bottom line is...it was fine....you drained it/topped up...it wasn't fine.

[nigelginny]

Right, heres an update, Haydn it looks like you were right, ive back flushed everything, i then re-bled the system exactly the way described on BF, the temp stayed at eleven oclock even at 2500 revs for 6 mins, i must admit there was some rusty coloured coolant when i backflushed but after about 30 mins it ran clear, i then took her for a 10 mile ride to get some antifreeze, and ten miles back, there wasnt any coolant loss through the expansion tank, or any visible leaks, i believe my problem was caused by an airlock, although i have been pm,d by another bongoer who had the same symptoms and sadly it turned out to be a new head, im not the main driver of our van my wife uses it very little, short journeys mainly, she has noticed that it has lost coolant and has just topped it up as normal (as i would have done), not knowing that loosing just a litre may introduce air into the system is something i think many owners dont know? I am today gonna purchase haydn's alarm, that way we wont asume that theres enough coolant.

[haydn callow]

You now say you have been topping up the coolant for some time....You need to find out why....fitting a Haydn alarm will stop you loseing more than about a mug full

[bigdaddycain]

Hi Nigelginny, you were right to increase the strength of the coolant, but there is a way of doing it with the bongo....

Basically, to avoid re-bleeding the sytem, the level in the expansion tank should never drop below the minimum mark...even for an instant, this gives air the chance to be introduced into the system, if the entire system is full of coolant, then air cannot be introduced, therefore a subsequent bleed wouldn't be required.

In other words, the coolant would need to be allowed to escape simultaneaously with fresh anti freeze going in the other end,maintaining a "full" level in the expansion tank at all times, a bit of a balancing act in other words, but entirely "do-able"

Your system will need to be bled, have a good read up on the factsheets, or type in "bleed AND air" or "seesaw AND method" or "hosepipe AND tank" or any combination into the search facility...Make yourself a brew and have a good old trawl through.