Black + Blue coolant caps and cooling issues...

[Mr Blue]

Hi all,

Burst another core plug today after a good caining on the way home. It is like the system just over pressurises but have replaced the cylinder head and gasket so gasses are not leaking into the cooling system.

My blue coolant cap always leaked coolant once I parked up. I noticed it was missing the rubber seal.

I fitted a black coolant cap off my other mk2 (which was running fine) and my core plug decided to let go with all the pressure.
I already replaced a core plug on this and now another has leaked where it was weak.

I can't understand how these coolant caps let out pressure? Is there a way to have a pressure relief built into the system and can it be found on another vag model?

I know the blue ones are the better ones but why have all my other mk2's been ok with the black one?

Annoying 

[raferackstraw]

i understood that the black ones did not have a pressure relief valve or faulty whereas the blue ones had a good valve. never had a problem with a blue one on my kr.

[tech1889]

Thats very strange you shouldn't ever really blow a core plug.. As you said the system is definitely running high pressure.. Maybe buy a new blue one with seal

[clipperjay]

Did you seal up the new core plug? Reallllllllll goodddddddd?   

[Mr Blue]

The new core plug has been fine. Its the next core plug thats gone.

New blue with a seal time. The plugs must have been badly corroded and finaly let go due to topping up with water when the cap leaked out my nice pink coolant. 

Hope its not an engine out job 

[mk2bal]

Something is impeding the flow of water I reckon. Thermostat faulty + not opening? Radiator blocked?

[tech1889]

Your core plugs sound like mk4 coil packs once one goes they all start going 

[Mr Blue]

deffo like mk4 coil packs 

new thermostat, water pump, radiator. Change the lot tomorrow hopefuly as they must all be corroded!

Guessing its just the three cores at the back of the block?

[clipperjay]

Just had to do the water pump recently aswell it started to rumble thought it was alternator changed it out no difference so must be water pump 

[tech1889]

Not sure whether 3 or 4 core plugs might be worth getting them done for peace of mind