What is this strange small pipe for?

Link to image   https://drive.google.com/file/d/1KFO2-DO2jCJ9hQ9L9tquZA4vZXH2qqYM/view

What is this strange small pipe near spark plug 1 for? Is it to do with the cooling system? I haven't done a coolant change for a while (garage usually does it when servicing) so I removed the small rubber cap over this tiny protruding pipe besides first spark plug expecting this might be an engine coolant outlet?  No coolant flowed from it when refilling or with the engine running hot.  Could someone tell me it's purpose please?

Could the strange small pipe be what's referred to in workshop manual " When the cooling water starts to overflow....from the port (2) provided at the engine side..."?  See this link  https://drive.google.com/file/d/1sDVf1RijA7C3ZS6GEkXoTqHmLEjJ75Yd/view

g149 wrote:.....  See this link  https://drive.google.com/file/d/1sDVf1RijA7C3ZS6GEkXoTqHmLEjJ75Yd/view

Above link may not connect. Try copy and pasting it.

Sadly, no - that refers to the cap on the metal pipe.

Can't believe no one in this magnificent forum can recognise and state the purpose of the small pipe besides first spark plug? (Link photo on first thread)

Hmm, that's interesting, was there a rubber tube connected to it?
Just replied to your message, I'll have a look at mine later see if I can remember anything about it

elfin girl wrote:Hmm, that's interesting, was there a rubber tube connected to it?

Yes, both PFM and myself have rubber caps on this short pipe.  My mechanic says it's a breather - but then why the cap?

Can't see one on mine, bit of a mystery