1997 Volvo S40 - What the heck is this plug ?

[blacktony]

hello !
yesterday i was investigating a coolant leak when i found this plug

before

and then in a few hours it popped out on the highway .. ofcourse that did not end well

after

.
my question is : what the hell is it ?
and can i just leave glued like i put it ?
thanks

[difflock54]

Its a venting valve for removing excess air trapped in the coolant system.
If they are not treated gently and cautiously I believe they can come away.
They do actually help with burping the system although gently squeezing the hoses themselves helps push any air up into the coolant reservour also.

[blacktony]

yeah... well eventually that s what i did .
So i guess i can leave it glued with epoxy like that .
Any type of hoses and small stuff like this are impossible to find.
Thanks for the reply!