Overheating Again!!

mobyfix · Post by **mobyfix** » Thu Mar 29, 2007 9:45 pm

actually

from reading the original post again...... an interesting bit i overlooked was the fact that he says the electric fan goes on ...missed that..Is that with the stat removed / with holes drilled or with the stat in place untouched.

I need to know where the thermo switch is......on the side of the radiator ?

Duncan

Dannyboy · Post by **Dannyboy** » Thu Mar 29, 2007 9:51 pm

Thanks for all the comments. The trouble is they all seem so convincing. I spent monday evening with the garden hose flushing and back flushing the radiator, the engine, the heater matrices and anything else I could find. The water ran clear at the beginning and at the end and there was no sign of blockages.

I will spend more time at the weekend looking further for a possible blockage in the bypass circuit. I will then use radflush or something similar on the system. If the new thermostat does not work at that point I will remove the radiator and get it flow tested, however if it is blocked I do not understand how the bongo will run with a "holey" thermostat.

I think the thermostat must be heated from above and the coolant is circulated by the pump as the water in the lower radiator pipe will only warm up once the thermostat is open.

I absolutely agree that it would be very worthwhile to get to the bottom of the overheating problems as soon as possible as it does to be a very common problem. The engineering company who checked my cylinder head and ordered me a new one told me his supplier, GTI possibly, had 40 bongo cylinder heads in stock as cracked heads were such a common problem.

The reason I am using a "holey" thermostat is not because I particularly want to, it is in order that I can use my bongo without overheating the engine. I will resolve the problem eventually... I hope. I'll keep you posted.

Dannyboy · Post by **Dannyboy** » Thu Mar 29, 2007 10:03 pm

Mobyfix, I've just picked up on your question about the electric fan. The fan does not go on with the holey thermostat or no thermostat. There are no overheating problems like this because presumably there is a good flow of coolant through the radiator and the engine is cooled effectively. In fact the engine probably runs below its optimum temperature as there is no reading on the temperature guage.

If a properly functioning thermostat without additional holes is fitted however, the thermostat appears not to open as the lower radiator hose stays cold. The engine then starts to overheat to the extent that the electric fan comes on to cool the coolant in the radiator, but as the coolant is not flowing through the radiator this will not help cool the engine. It is time to switch off and nurse the bongo home to try again.

Hope this makes sense.

haydn callow · Post by **haydn callow** » Thu Mar 29, 2007 10:42 pm

This is by far the most interesting and informative topic I have come across to date on this forum. I downloaded the coolant chapter from the NZ workshop manual site and what has been discussed and discovered all adds up. As far as I can see the stat is indeed located where the lower main hose enters the engine. If this stat is not opening it can only be for one of two reasons. (1) it's bust (2) the heated coolant that opens it is not reaching it. As in this case all is well with stat out or a hole drilled in it the main circuit must be free of obstructions. So ! somthing else must be the trigger that opens the stat, i.e. a bypass circuit. Find this and make sure it is clear and in theory all should be well. All this has been stated before in this topic. Just thought I would let you know even a numpty like me is beggining to see the light due to all your comments.

Vanmanerik · Post by **Vanmanerik** » Thu Mar 29, 2007 11:16 pm

I had a look around the engine compartment today, tried to take some photos of the thermostat housing and circuits coming off it but no good they were not usable . It looks like one is just a bypass circuit, another is a cooling circuit for the turbo-charger, and the other for the cab heaters.

I also started my engine and waited for the bottom hose to get hot, I gave up in the end after about 20 mins, the temperature gauge was on the 11 o'clock position which for my Bongo is normal so I can only assume that the flow through the heaters, the turbo and the bypass is enough to keep the engine below 82 degrees so the thermostat never opened. I assume that under road conditions the engine would get hotter and eventuall the thermostat opens. A very strange set up.

mikeonb4c · Post by **mikeonb4c** » Fri Mar 30, 2007 12:22 am

I noticed too Vanmanerik that the tem gauge doesnt seem to move off the stops even after a v long time at tick over from cold. Move off, and up it comes. Also, when bleeding, the runs at 2500rpm as instructed by workshop manual had it coming off the stops no probs. As you say, a strange beast.

francophile1947 · Post by **francophile1947** » Fri Mar 30, 2007 12:26 am

On tickover you are not putting the engine under load and not using much fuel, hence less heat is generated.

grumpo · Post by **grumpo** » Fri Mar 30, 2007 1:14 am

Quite right Francophile, a point worthy of note.

The gauge needle starts to rise from the stop at around 40 degees C.
Running a really cold engine at tickover could take up to 15 minutes to
achieve this low temperature. You should get in and drive it as soon as
possible after starting it, less pollution and less engine wear.

I do not understand why some members consider the Bongo cooling
system to be "Strange", it's not that much different to a lot of modern
systems. It's simply a case that the engine is situated behind the main
bulkhead and requires some complicated pipework to connect to the
radiator and the additional cab heating and cooling systems, which are
not normally fitted to less well equiped vehicles.

alphabetter · Post by **alphabetter** » Fri Mar 30, 2007 8:24 am

Vanmanerik wrote:I had a look around the engine compartment today, tried to take some photos of the thermostat housing and circuits coming off it but no good they were not usable . It looks like one is just a bypass circuit, another is a cooling circuit for the turbo-charger, and the other for the cab heaters.

Yes very hard to get a photo. Here is my attempt.

mikeonb4c · Post by **mikeonb4c** » Fri Mar 30, 2007 11:58 am

grumpo wrote

I do not understand why some members consider the Bongo cooling system to be "Strange", it's not that much different to a lot of modern systems. It's simply a case that the engine is situated behind the main bulkhead and requires some complicated pipework to connect to the
radiator and the additional cab heating and cooling systems, which are
not normally fitted to less well equiped vehicles.

I think the word 'strange' is being used lightheartedly. However, just as with any system (motorways, Wide Area Networks), the more 'nodes' it has, the more difficult to diagnose the precise cause of a malfunction tends to become. In such cases, consumers have been known to find the behaviour of the system 'strange'. The Bongo could possibly qualify as have a number of nodes (i.e. interchanges across the cooling system)

Time to stop being deep now Mike and get back to the surface for air

Vanmanerik · Post by **Vanmanerik** » Fri Mar 30, 2007 3:18 pm

Well done alphabetter, a good photo.

Grumpo, I will tell you why this cooloing sytem is 'strange' - usually the water circulates from the hot top of the engine, through the radiator where it is cooled, and then through the bottom hose back to the base of the engine where the whole process starts again.

The Bongo is 'strange' because the water never seems to circulate at all through the radiator!

I did a test today, and I ask all of you to do similar and post your results here on this forum.

My test:- Drove the Mrs 2.5 miles to her Belly Dance class, tested the top and bottom hoses her - top hot, bottom cold. Drove a further 1.5 miles to ASDA, restested hoses - top hot, bottom cold. Left Bongo for 20 mins and then drove another 1.5 miles to see my mate Mick, top hot, bottom cold. left van 15mins, drove another 2 miles to B and Q, top hot, bottom cold, left van 5 mins drove 1.5 miles to home, top hot, bottom cold. All the above driving was in town so no fast roads. The bottom hose never even got warm as if the water had passed through the rad and had been cooled down, it was cold.

So is the radiator / thermostat only there for the times when the engine may overheat, say on a hot sunny day? Today was cool, the temperature gauge was showing normal, the heaters all worked fine, so is it that just the engine bypass circuit and the heater circuits are sufficient to do the cooling?

Now I say this is 'strange', 'very strange'.

So can you all do a similar test and see if it is normal for the bottom hose to be cold.

Please see poll in another thread.

francophile1947 · Post by **francophile1947** » Fri Mar 30, 2007 3:27 pm

That is weird Vanmanerik. If the radiator is rarely used, the lack of through-flow could explain why they seem prone to blocking.

mobyfix · Post by **mobyfix** » Sat Mar 31, 2007 8:44 am

Dannyboy wrote:Mobyfix, I've just picked up on your question about the electric fan. The fan does not go on with the holey thermostat or no thermostat. There are no overheating problems like this because presumably there is a good flow of coolant through the radiator and the engine is cooled effectively. In fact the engine probably runs below its optimum temperature as there is no reading on the temperature guage.

If a properly functioning thermostat without additional holes is fitted however, the thermostat appears not to open as the lower radiator hose stays cold. The engine then starts to overheat to the extent that the electric fan comes on to cool the coolant in the radiator, but as the coolant is not flowing through the radiator this will not help cool the engine. It is time to switch off and nurse the bongo home to try again.

Hope this makes sense.

Where is the thermoswitch to switch on the electric fan???....on many cars its on the radiator.... which would be interesting !! I suspect it is on the engine block in this case as it shouldn't go on if the radiator is cold.

Normally they design it so the thermoswitch tests and switches on the radiator tempeature ---- coz the fan only cools the radiator !! seems stupid to put the switch elsewhere as it ends up turning on a cooling fan to cool a cold radiator !

So..... someone.... where is it ?

Duncan

mikeonb4c · Post by **mikeonb4c** » Sat Mar 31, 2007 9:08 am

I wonder if bj4 could find a friendly Japanese mechanic who has worked on Bongos for many a day and might be persuaded (for free BF membership and a bottle or two of saki) to contribute an agony column. Wouldnt that be fun.

Taxiback · Post by **Taxiback** » Sat Mar 31, 2007 10:28 am

I think the thermoswitch to switch on the electric fan is at the rear of the block just above the hose to the rear heater above the starter motor.
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Overheating Again!!

Hot engine

Re: Hot engine

Hot Engine.