Bongo Fury

I imported my Bongo myself. It arrived in July 2006. It is in pretty good condition and has now done 53,000Km. At no time has my bottom hose ever warmed up when a thermostat has been fitted.

I was concerned about overheating and ran it for about 6,0000Km without a thermostat. I had a burst cylinder head gasket which once the cylinder head was removed turned into a cracked head. I changed that. Thanks to Declan Hicks for his useful factsheet. It was not difficult, but required great care. I don't know whether it was like this when I brought it in or whether it cracked over here. The thermostat turned out to be faulty, or at least tempremental, as it opened or possibly did not when checked on diffeent occasions

I replaced all belts, the water pump, and have fitted a new thermostat. A number of times! I bleed the system very carefully, make sure the front and rear heaters are blowing hot, but the only way I can get the lower radiator hose to warm up is to either not fit a thermostat or drill a few holes in one. Otherwise the temperature guage swings beyond the central point of the guage, indicating overheating. The radiator fan will also come on indicating the engine is too hot, but the lower hose remains cool. There is no point in having the fan operating if there is no flow through the radiator.

This suggests to me that the thermostat is not opening. It is fine when tested in a pot of boiling water, opening wide at about the 82 degrees temperature. Has anyone else experienced a similar problem?

My solution is to fit a new thermostat with about 4 small holes drilled in the perimeter. Eight holes are too many as the lower hose warms up but the coolant does not warm sufficiently to register on the temperature guage. The vehicle will run fine like this, but I can never be sure my temperature guage is working, and there is always the possibility that if the engine does overheat I will not be aware of it.

Any ideas please?

As you can imagine I now have lots of experience of removing and replacing he thermostat. In various places it is suggested it is necessary to remove a propellor shaft to gain access to the bolts below the thermostat. I used a universal socket with my socket set very successfully, doing away with the need to remove the propellor shaft.

Any advice will be gratefully received.

Cor - a real brain teaser. And are you absolutely sure you have free flow through the block, radiator etc.? I nearly tried to put my thermostat in the housing upside down - not sure if it would have allowed itself to be tightened up that way but its the kind of daft thing I'm capable of from time to time. I hope someone who understands these things properly may come to your rescue and good luck.

Mike

I have a new thermostat, radiator and head and the bottom hose remains cold when left ticking over on the drive.
Don't know about on a run.

Last night I fitted a new thermostat, bled the coolant system, waited for the temperature to come up, the front and rear heaters to work, then took it for a run. It immediately started to overheat. So back home. The top hose is hot, the lower hose cold, so there is no flow through the radiator.

This morning I fitted another new thermostat with five small holes drilled round the perimeter. Went through the same process and the bottom hose warmed up, therefore there is a flow through the radiator. Drove about 80 miles through the Trossachs, a beautiful area north of Glasgow, and had no overheating. The temperature guage varies widely from registering cold on long downhill stretches to registering normal on long uphill stretches.

I could drive like this for ever, but I'd rather get my thermostat to open normally. I checked whether it could be fitted upside down, but this would be impossible. I checked the inside of the thermostat housing using a mirror and torch but it looks fine, with no obvious blockage.

What next? I wish I knew!

It must be the thermostat not opening properly, musn't it?
Are you sure it's the correct thermostat? Have you been able to test that it opens and at what temperature?

hi danny boy
ive experienced the exact symptoms , new head , new thermostat,new rad, still over heated then new water pump & second thermostat had it back 10 weeks now with no probs fingers still crossed could your rad be at fault mine was full of sludge and told it was impossible to re core cos it was too bad . mine also ran fine without thermostat in couldn't understand this either. driven aprox 1500 miles since fixed now seems ok.
it still worries me as i never got a definitive answer to the problem.
good luck with yours, would love to know what the problem is if you find out

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simon

I'm bongoing mad R U?[/b]

Hi Simon, Francophile,

I'm sure it is the correct thermostat. i've bought two new ones and both are the same as the one that came out. They both open at around 82 degrees.

Simon, do you think the problem is with the radiator? When I do not have a thermostat fitted, or I use a thermostat with holes then the bottom hose gets warm/hot. It is only when I use a proper thermostat that I get the overheating and the bottom hose stays cold.

When I ran it today, not under load and going generally downhill, the temperature guage dropped noticeably. This would suggest that the radiator is working OK. Certainly when I run a hose in the top or bottom of the radiator, the water coming out the other end is clear, but possibly it could be bypassing the core or only passing through part of it.

My gut feeling is that the thermostat cannot be opening properly, but at the same time this seems unlikely.

Dannyboy wrote:My gut feeling is that the thermostat cannot be opening properly, but at the same time this seems unlikely.

I think you're right, even though it is very unlikely that it is happening with 2 thermostats. Let's face it, if the stat was opening, the flow of water would be greater than through a few small holes drilled in it. As the water is circulating with the holes drilled, it doesn't sound as if the stat is actually opening.

hi dannyboy
my radiator also looked as though the water was clear when i flushed it no sign of any blockage i was only told the rad was in a bad way by my mechanic after head and thermostat was changed and still overheated.
even though i had a new rad it overheated again and then i replaced water pump against the mechanics judgement and 2nd thermostat did not expect this to solve the problem but it seems to have only wondered if it could be your rad as it seems to be the only thing i changed which you haven't. leads me to believe that my entire cooling system needed changing.
best of luck

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simon

I'm bongoing mad R U?

This is an absolute mystery!
Simon, I would agree with you if it wasn't cooling down so much when going downhill - wouldn't this indicate a good flow through the radiator? Can you get a radiator flow-tested, or could you run hot water through it and feel for cold spots?
If I had more hair I think I'd be tearing it out!!

hmmmm.... logic tells us that the temperature at the top of the thermostat never reaches the 82 degrees to open it... so i would be looking at a circulation problem... not having had my bongo for long i haven't worked out where the water flows. Really you need to draw up a chart to work out why the hot water doesn't reach the thermostat... somewhere in the cooling system is blocked i guess....

hi francophile
when mine was first over heating i also had wide fluctuations of temp which made me think of a faulty thermostat ( going up one hill it would overheat turn right normal temp etc, heaters blowing hot one minute and cold when overheating) i had no usual blown head symptoms and every thing we tried failed until every thing had been changed ( desperately touching wood as i speak) still afraid to say that it is finally fixed.
i had my rad flow tested at a local radiator manufacturer(newquay radiators)

________________

simon

I'm bongoing mad R U?

actually i will try and expand on my last post........your bongo has two main cooling circuits..... the first minor circuit ( for when it is cold ) does not take the coolant through the radiator... but it goes across the top of the thermostat..... when the temperature at the top of the thermostat gets to 82 degrees it opens...... and the main cooling circuit is used....IF the minor circuit is blocked and the flow is restricted then the temperature at the thermostat will not reach 82 degrees.....( imagine this circuit at a Y with the bottom part being the thermostatic valve - the water flows past the valve until it opens.... then it can flow down into the main cooling system ) if the hot coolant doesn't flow past the thermostat it won't open

So, by making holes i the thermostat or removing it allows the larger cooling circuit to be used full time and hides the blockage in the small one....

please correct me if this doesn't make sense...

Thanks for clearing that up Simon - puzzling ain't it?
I have never seen a system like that mobyfix, but I ain't needed to work on cars for many years so you could well be right.
So Dannyboy, it looks like a flow test of the radiator is needed.

Thanks for all the advice. Having spent some time on this now, I can confirm that Mobyfix's description of the cooling system is correct. The flow to and from the front and rear heaters is via a hose at the front top left of the engine which splits in to two, one hose going forward to the front heater and the other going back to the rear. Once through the heaters they join again and enter the engine low down at the rear right.

This allows the heaters to work even though the whole engine/cooling system is not up to temperature. Once it is, the thermostat opens to allow water to flow through the radiator to cool the engine and keep it at the correct temperature. Without looking at my engine I cannot picture exactly where the hose leaves the front of the engine to reach the top radiator hose, but once it has, it flows back out of the lower radiator hose to the engine, entering directly below the thermostat.

When bleeding the system, both front and rear heaters work effectively which suggests to me that the system is not blocked and the water at the thermostat housing should be at 82 degrees.

I am not sure what to do now. I think I will get my garden hose out and try to clear out every water passage I can. I'll then take it to a radiator specialist and ask them to check the radiator.

If all else fails I'll do what I've done for the last two days. I'll fit a thermostat with a few holes round the perimeter and accept that the temperature will fluctuate as I drive. I've done 200 miles in this fashion in the last two days. I'll be disappointed to do this because I won't have solved the mystery, but I'll accept it.