how does.....

Spammer Joined: 27 Jul 2004 Posts: 5717

the pressure cap work ?

i got the blue one as you do on the valver even though it builds up pressure in the system when hot ,it makes funny hissing noises when a water pipe is squeezed when cold .now comparing with my 1.8rt (which has the brown cap ) this feels a bit not right .

now what i want to know is ,how does this pressure cap thingy work ? does it also release unwanted pressure from the tiny hole in the middle of the cap or what ?

Site Subscriber Joined: 25 Nov 2004 Posts: 350

bit like a thermostat i thought Shocked

part inside the cap opens/expands when the pressure/heat builds up and then lets it pass through slowly. If im wrong im sure it will be made known before long Laughing

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

springs. theres 2 springs in the cap and 2 valves. 1 the big one is the pressure spring. The other is the vacuum valve, lets air in as the coolant cools etc.

The small vacuum spring can clog and thus jam and allow no pressure to build up.
You can take it apart and clean it.

Pop the colouired bit off then clean it all with a tootshbrush. To get the small valve apart squeeze the tags together to pop the spring and washer off.

Bear in mind not all caps can be sorted, some are damaged beyond repair.

Spammer Joined: 27 Jul 2004 Posts: 5717

just as you said sir ,i popped the cap out and came out a spring everywhere was full of surface rust .came out easy after wiping .

cleaned all nicely and stuck it back on the tank ,more pressure seems to be building up .nice Laughing

the brown cap has a shorter spring inside compared to the blue one btw

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

yes thats why they are rated differently!

Spammer Joined: 27 Jul 2004 Posts: 5717

nice one chris ,