Expansion tank cap wrong pressure

[Paltibine]

I've noticed that my expansion tank cap is marked as 0.9 bar but I have read that it is supposed to be 1.1 bar. This is for the 2.5l diesel engine.

Does anyone know exactly what difference that 0.2 bar really makes? I have been having coolant loss for some time but no sign of it coming out via the expansion tank. In fact I'd just bought a fluorescent marker die to use put into the cooling system to try and trace the leak. Perhaps I won't need this now?

Looking on ebay several people are selling 0.9 bar caps for the bongo so do I need to change it as I must have done several thousand miles with the existing one.

Thanks.

[Northern Bongolow]

Years ago I fitted a pressure gauge to watch the internal pressures to relate to temps seen whilst driving.when fitted to a good system the temps seen and the internal pressures were well under the cap pressure blow of setting, the problems seem to occur when things were not maintained, temps go up or are not controlled quickly enough. When temps go up so does the pressure. When the bongo diesel is at it hottest, after working hard and ticking over, no airflow through the rad because it's parked or moving slowly, front fans on low, on/off trying to cool things down the internal pressure is just below 1 bar, it would only take a older rad, or an older stat, poor quality coolant, etc to push it over the the 0.9 cap setting, even the 1.1 cap.
I used the pressure monitoring more than the temp gauge measurement because pressure is a full system measurement rather than a locally measured temp sensor.
I also made a tank cap testing device and that about half the caps I tested for people at club meets failed, they either blew off early or failed to close quickly after venting, from that I decided that as it's the safety device on the system that it would become part of my regular service swap items .

[Chris Bongo]

Where do you recommend getting a new 'OEM style' replacement Northern Bongolow?

[Ian]

Choice of after-market or genuine Mazda in Bongoland at https://bongoland.co.uk/product-categor ... em/page/2/

[haydn callow]

Depending on the type of radiator fitted, if the rad has a vent like the expansion tank, I would expect the rad to have a 1.1bar cap and the tank a 0.9bar cap.........you don’t want the rad to vent before the tank. If the rad is the non venting type I don’t really think it matters much which cap you have on the tank as long as it’s sealing and venting properly.

[Paltibine]

Thanks everyone for your comments!

The cap on the radiator is 1.1bar but I don't know if it's a sealed one or sprung and I'm too scared of getting air in to take it off and look!

Doesn't sound like it's a really big issue but I get the impression it probably won't be the culprit for my leak.

I guess I should check the radiator one and if it is sealed then I should get a 1.1 bar cap for the header tank.

[haydn callow]

To check the rad, look at the neck below the cap, if there is no spigot then you have a sealed rad and you can put a non pressure cap on.
However, I would just leave everything as it is.

[JulesMartin]

Hi, Just had to bleed out my Bongo this afternoon and this evening rechecked I'd done everything right by watching the 3 utube videos. I notice in the video's that the Bongo does not have a pressure cap on the rad. mine has a pressure cap on both the rad and expansion tank and both are marked up at 1.1bar. there is no overflow pipe from the neck of the rad to the expansion tank. there is a 1" hose running from the top of the rad to the middle of the expansion tank and a 1/2" hose coming from the bottom of the expansion tank disappearing back towards the engine. is this correct to have two pressure caps on this system? I'm thinking not and that the rad should have just a flat cap. Bongo is 2.5 TDi 1996. Any advice as always much welcome.

[Northern Bongolow]

The rad can have either a flat cap or a pressure release cap it does not matter on the rad as the filler neck is a different design or each, the rad has no bottom seat for the pressure seal to sit against, it just uses the top cap seal to seal the rad. The expansion tank has a duel seat, one at the top and a lower seat flange for the pressure seal to sit against. This is all presuming the rad has no spigot at the side of the rad filler cap which a standard spec bongo rad does not have but may have had a non standard rad fitted in a past life. If it does have a spigot at the side of the rad filler cap this must be blanked off using a short pipe with a bolt inserted and clip to stop it possibly vent under work. All venting is done at the expansion tank, this complex cap is also the cap that allows air to enter when the system is depressurising when cooling, you may here it doing this at this time of year as the coolant quickly cools down, you may hear it make a 1 second groaning noise as the coolant cools, this is cap allowing the coolant pressure to return to atmosphere pressure or just above.

[Bob]

Those long pipes go to the rear heater.

This is sometimes removed when a conversion is fitted or sometimes just capped off because of a leak.