ANOTHER OVERHEATING BONGO, HOPEFULLY SORTED

dandywarhol · Post by **dandywarhol** » Fri Apr 06, 2007 11:24 am

Phew.......just returned from a few days away and tried to get my head round this thread

......jamesnjane, the hole in the stat is to help air pass through the stat when bleeding/filling the system.

What's interesting me is hadyn's theory that the coolant path is from the BOTTOM of the radiator to the TOP.......

haydn callow · Post by **haydn callow** » Fri Apr 06, 2007 12:12 pm

POST EDITED TO CLARIFY COOLING SYSTEM DISCUSSION: OOp's. I did say earlier that I have misunderstood Al at Allans Vehicle Services instructions. I apolgise!!
Well I misunderstood and I do apologise.
Dandywarhol has consulted Allan the oricle and I am sure he will post a reply explaining all.
Sorry again but it did get you going. I had a red herring in my tank. I will shut up now on this subject.

The debate that follows is based on misunderstanding, as explained in the edit above.

dandywarhol... Yes that was the opposit to what I thought but now I've got my head round that things make more sense. The Bypass circuit leaves the cyl head and then appears as the smaller of the two pipes on the side of the expansion tank, coolant then leaves this tank via the larger hose and goes to the top of the Rad next to the main top hose by which means it returns to the cyl head.

Vanmanerik · Post by **Vanmanerik** » Fri Apr 06, 2007 4:23 pm

Copied from another lead on the forum as I thought it bore more relevance here (Erik)

This Bongo cooling problem is a real pain, the only way for you to diagnose it is to take your rad. off, block the bottom outlet, stand the rad upright and pour hot water in through the filler hole, now feel the rad and see if it has any cold spots, if so it is blocked in this area.

Looking at other threads in the Forum covering overheating you can see where people have replaced their rads and are still having overheating problems.

I think what I would like to do is:
a) Install a piece of 'see through' hose somewhere in the top or bottom pipe so you can observe if the water is flowing, if it flows you should not have a problem, if it doesn't flow when the engine is hot then the thermostat needs checking to see if it is working OK, if it is OK then the radiator needs flushing and cleaning out or replacing.

b) If after carrying out all the above then I would think that fabricating a thermostat housing that will fit in the top hose and removing the thermostat from the bottom hose would be worth a trial.

Its a lot of work, so do I leave it and take a chance, I am not overheating but I am one of the top hose hot, bottom hose cold category.

or

Does anyone know if you can get thermostats that open below 82 degrees.

If so the if we all buy one of a different 'size', say 70 to 82 and fit it to our Bongos we can report back and see if the bottom hose is getting warm.

haydn callow · Post by **haydn callow** » Fri Apr 06, 2007 4:56 pm

vanmanerik... Thats the way it should be. Top hot /bottom cold. If and when you stress the engine enough to open the stat it will be hot/hot. Try letting the engine idle for about 10 mins then rev at about 2500 for five mins. Observe the system pressurising and the expansion tank getting really hot. Soon the stat will open and hot water will go along the bottom hose into the bottom of the rad and up to recirculate.

Vanmanerik · Post by **Vanmanerik** » Fri Apr 06, 2007 6:00 pm

Thanks for that info Haydn.

Unfortunately I could run the engine for a month on idle and then run at fast speed and the bottom hose will not get hot, can fry an egg on the top hose!

As for the water flowing hot along the bottom hose to the rad I think you are off the mark there, water flow is more likely out the top of the cylinder head, top of rad, bottom hose back to thermostat, return to base of crankcase.

I have tried everything in my extensive knowledge - I have maintained / repaired all my own vehicles since 1968 from a Standard 10 through to a Skoda Octavia - but the Bongo is a real pig where overheating is concerned.

Normal logic does not seem to apply to the Bongo setup.

I am sure that with enough of us now contemplating this problem we will through trial and error and sheer bloody mindedness find a long lasting cure. I just can't imagine why this has gone on so long without a solution being found.

What we really need is feedback from all the failed Bongos, what was done to correct it and did it work successfully, i.e.

People with cracked heads - did they check the old head for blocked water channels???

People who replaced thier radiators, did they check it for blockages? Did a new rad cure the problem?

Did a replacement thermostat cure the problem?

Did a whole engine clean and flush remove much crus? Did it cure the problem.

How can you tell if the water pump is not working?

If we had these answers we can start building up a picture of common problems and cures.

haydn callow · Post by **haydn callow** » Fri Apr 06, 2007 6:07 pm

The bottom will never get hot on idle unless somthing is wrong. The engine must be well reved for quite a while before the stat opens and the bottom hose will then get hot. This is as it should be.

Peg leg Pete · Post by **Peg leg Pete** » Fri Apr 06, 2007 6:14 pm

Well after a long spell of overheating, I replaced the thermostat,tested old one it was opening very slowly and probably not to fully open. once I fit the new one, did a thorough rad flush, bled the system, not from the manual, did not have that info to hand. I have had a year of normal temp running, I put it down to sludge in the system, that was restricting coolant flow, poor stat operation and leaking radiator and expansion bottle caps. I also replaced a few hoses that were a bit dodgy looking, one had a pinprick leak that was not obvious when the engine was not running.

Vanmanerik · Post by **Vanmanerik** » Fri Apr 06, 2007 6:58 pm

Just found a good article of a similar problem on MGF car. Its well worth a look at as it offers good reasons for heads cracking on engines with themostat on lower hose, good test data to prove it, and an inexpensive answer.

http://www.mgfmavhh.ukf.net/

What doo you think?

haydn callow · Post by **haydn callow** » Fri Apr 06, 2007 7:02 pm

Hi !! me again, this is going to be my last post on this subject co's I now find I'm repeating myself to no avail. If you read Bongopatrol's comment on the other topic Poll. is your bottom hose hot/cold. He states he went for a 85/90 MPH drive down the motorway and idled in traffic for long periods.. His bottom hose was only cool and his temp gauge rock steady at 11 o'clock. That tells me that his stat was closed and coolant was not circulating round the main circut or through his rad.His engine was being cooled by 1, the bypass flow, 2, airflow round the engine, 3, fans. his engine is I would think in good condition and free of crud. This is how my Bongo behaves and I suspect the vast majority of the thousands of Bongos out there. F1 cars are well thrashed and only rely on airflow/oil coolers.

Jamesnjane · Post by **Jamesnjane** » Fri Apr 06, 2007 7:04 pm

temp gauge just slightly lower with new rad, so maybe was a little blocked, sticking with the holey thermostat for the time being until i have time to mess around again.

Vanmanerik · Post by **Vanmanerik** » Fri Apr 06, 2007 7:18 pm

Hi Haydn, I like your latest theory - so why bother with a radiator at all?

Me thinks there is more to it than meets the eye.

Jamesnjane · Post by **Jamesnjane** » Fri Apr 06, 2007 7:39 pm

vanmanerik, thats a quality article well found, thats what iv been thinking, no where near as in depth as that, but that the bongo cooling system isnt upto the job, yeah yeah i know thousands of bongos are running fine at the moment, but it seems to be a common problem with bongos no one can deny that.

haydn callow · Post by **haydn callow** » Fri Apr 06, 2007 7:40 pm

o.k. just one more.I read the MGF link and it is a very well researched topic. However does it apply to our Bongo's?? If the the system works the way I am suggesting, then as the stat rarely opens under normal conditions thermal shock will not be present, and when it does open it is to let hot coolant pass downwards to the bottom of the rad, as the top of the rad is already hot due to the bypass circuit passing through it only hot coolant will be sent to the cyl head.

Vanmanerik · Post by **Vanmanerik** » Fri Apr 06, 2007 7:53 pm

Haydn, what makes you think the water flow is from the thermostat to the bottom hose and then UP the radiator to the top hose to the engine??

Explain please and then maybe I can see where you are coming from..

Jamesnjane · Post by **Jamesnjane** » Fri Apr 06, 2007 7:56 pm

i ran the bongo today with new rad and holey stat after a run the top hose hot the bottom hose warm so the flow is going from top to bottom right?????

ANOTHER OVERHEATING BONGO, HOPEFULLY SORTED

Over heating.

Hot engine.

Overheating.