Overheating /Over Pressurised 1996, 2.5TD Bongo

[surfkernow]

Hello, two years ago, I was active on the forum as my Bongo was throwing coolant out of the expansion tank; after months of stress, a new cylinder head solved my problems. A new radiator, thermostat, water pump, low coolant alarm, haydn cylinder head temperature gauge, were also added to my Bongo. All the coolant pipes were replaced, and a self bleed kit was fitted. I had just spent 1300 on welding a month ago (rear arches + MOT), and now by Bongo is begging to show similar symptoms to two years ago.

My average temperature has gone from 84 to 89, and if I idle or get caught at 4 way traffic lights the temperature can climb to 95, when it used to just sit at 88. As soon as I start to drive, the temperature will start to come down to 85. Basically, I need to drive to stop my Bongo getting too hot. All my coolant hoses are now rock solid, after a short 10 minute journey. When I turn off the engine, I can hear the dreaded gurgling from my expansion tank for about 15 seconds. The pressure in the pipes will remain when cold. If I do take off the expansion cap, there is a massive release of pressure, and you can hear gurgling from deep within the engine. This is all new behaviour. Also, the blowers blow hot air when my foot is on the accelerator, but blow cold warm as soon as I idle at traffic lights or remove my foot from the accelerator.

I replaced the thermostat, and have also replaced both the temperature sensors, but to no avail. I have put UV dye in the coolant system, but have yet to find a leak. In fact due to how much pressure is retained when my Bongo has sat for days, I am pretty sure there is not a hole anywhere, or my pipes would not be rock hard.

I am thinking, head gasket /cracked cylinder head, but I would like your advice. My last cylinder head was brand new from Bongo Spares, not a cheap copy.

I feel like an expert in troubleshooting after my last head failure, but like last time, my van has technically never overheated, as my alarm set at 101 was never triggered when my last head was replaced . This time is the same, the highest it has been is 95.

Apologies for the long post, I am trying to cover everything. There is a slight decrease in power when driving. Leading up to me noticing this problem, my Bongo went through a period of just not starting over a period of 8 weeks , I could turn it over 10 times in 10 minutes, and just a click noise and nothing, this was becoming more and more frequent. I thought, fuel pump leak again, or the sensor under the gear stick etc. But, as soon as I replaced the thermostat, and changed the coolant, it starts everytime without fail. I can't see how the two are connected, but it was odd.

Anyhow, any pointers greatly appreciated, before I changed the cylinder head again, or at least take it out to be tested.

[g8dhe]

I wonder if your water pump could be having problems and your only get significant coolant flow thru the engine when your rev's go up ? In the past there have been reports of pumps missing vanes etc. which can lead to these sorts of problems ?

[surfkernow]

Hi Geoff, thank you for your reply. The water pump was replaced by a Bongo specialist 2/3 years ago, but it could be failing. Is there a way to check?

Someone on another forum has mentioned the front heater matrix could be clogged and could I temporarily by pass it. Is this possible?

I should have mentioned, I bypassed the rear heater matrix 2 years ago.

Off to bed now, but a full day of bongo troubleshooting tomorrow

[g8dhe]

Heating matrix problems normally only report lack of cabin heating problems, rather than engine overheating problems.
The pump makes me suspicious because your overheating seems to occur when stationery, which could be because fans aren't coming in on the radiator itself to cool the coolant but you make no mention of that so I assume your fans are switching in as expected ?

[teenmal]

I would think your system over pressurizing rather than temperature rise is the problem , have you checked the cap on the expansion tank .Its also worthwhile having a sniffer test done this will show you if any gases are in the system.

good luck

[surfkernow]

Hi Geoff thank you for your reply. I was up early and managed to get to the heater matrix pipes. After a short 10 minute drive, they were both hot. So I suspect you are right to discount the front heater matrix, which is good as it looks like a bugger to disconnect.

Both the fans behind the radiator do kick in. I am about to spend the afternoon, trying to get to the water pump, to see if I can see any leaks. Is it easy to tell if it is seized, without removing the pump.

Teenmal. I went down the sniffer test two years ago, it passed and I still had a head failure, so I am going to leave that as a last resort. You ars correct, it is a pressure problem, as well as an overheating problem.

How would I test the expansion tank cap?

Thank you

[Bob]

If the water pump was seized I think you would get a loud shrieking from the drive belt sliding over the pulley.

[surfkernow]

Hi Bob, thank you for your reply. No shrieking, so I presume it is not seized. It is only two years old. I am going to get a mirror down there now and see if I can spot any leaks

[g8dhe]

There have been cases where the vanes inside shatter/destroyed and hence it spins happily without pumping as much coolant.

[surfkernow]

Here is a photo of my waterpump from underneath. Does that look like it is leaking?

https://postimg.cc/gnj6WHv7

Higher resolution

https://postimg.cc/D84y6jQ7

It is certainly wet below the housing. Albeit everything is covered in oil, so when you touch it, you just get wet oil. It is not glowing with my UV torch

[g8dhe]

You didn't originally say you were loosing coolant ? Merely that it was ejecting coolant, which could be from overheating due to slow moving coolant boiling or as mentioned previously a crack with exhaust gases pressurising the system.

[teenmal]

Hi Geoff thank you for your reply. I was up early and managed to get to the heater matrix pipes. After a short 10 minute drive, they were both hot. So I suspect you are right to discount the front heater matrix, which is good as it looks like a bugger to disconnect.

Both the fans behind the radiator do kick in. I am about to spend the afternoon, trying to get to the water pump, to see if I can see any leaks. Is it easy to tell if it is seized, without removing the pump.

Teenmal. I went down the sniffer test two years ago, it passed and I still had a head failure, so I am going to leave that as a last resort. You ars correct, it is a pressure problem, as well as an overheating problem.

How would I test the expansion tank cap?

Thank you

You are perfectly correct , the test will show if it has gases it will not show that it doesn't have gases, its a one way test. Regarding the water pump you can test them various ways (just think pump )you could disconnect a suitable hose and start the engine .you can also tell by removing radiator cap and watching the flow ,the cap can be tested with a pressure gauge but I would strongly advise replacing them as a matter of course especially after a replacement head has been fitted.

[surfkernow]

Hi Geoff, it is not throwing coolant out of the expansion tank, that was a reference to my problem two years ago.

I am on my way back from Euros with a new water pump. I will try and fit it tonight /tomorrow.

Thanks Teenmal. I will try out another cap. I think I have a selection from a few years back.

I am just going to swap out various parts until I am just left with the Head as the only possibility. Two years ago I did this and ended up spending 600-700 pounds on garages going it could be the : radiator, thermostat, water pump etc. I can change them all myself for a fraction of that, so I am just going for it this time. I don't want this to turn into another 4 month saga.

Thanks for your help guys

[Hazzobongo]

I feel your pain mate, its bad enough having one head letting go without having another a couple of years later. I've just bought the bongo but had the same problems with a hilux surf ten years back so I'm in the process of installing temperature monitors along with the already installed low coolant alarm so I can pull in and let the system cool right down rather than continue till the head goes pop.

Till someone can actually pinpoint the reason why or find out if these initial heads are just weak I reckon we're all stuck with the paranoia.

[surfkernow]

Thank you Hazzo. Waterpump installed, will test tomorrow night.

Can I suggest you fit a High, coolant alarm as well.

When my last head cracked, my Haydn Alarm was never triggered, as it did not get hot enough. The low coolant alarm was never triggered, as the system was over pressurised, and pushing the coolant out of the expansion tank.

The low coolant alarm is good if you have a leak.