Expansion tank cap

[lodgey62]

Was running the van stationary this morning as l do every week and water started to leak from the upper expansion tank filler cap,took it off blew down the rudder valve things and now seems to be ok but I'm going to buy a new cap as lm sure that's the original one,is it a know issue and am l doing the right thing?
Regards
Lodgey

[boatbuilder]

Is it connected via a pipe to the tank behind the flap? The idea is that when the pressure gets too much in the main tank the valve in the cap allows some coolant out into the tank behind the flap. Then when it all cools down and contracts it sucked it back the other way.
If in doubt best to replace it but beware of bad quality caps that don't work even when new. The brand to go for is Blau. Don't bother with any other.

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[lodgey62]

Cheers Boatbuilder,my thoughts exactly, putting my brickworks order in now.