Seems like you nailed it with the cap suggestion Marc.

Should the bleed valve open and close on its own, with the bow in the down position?

2000 Boxster S Arctic Silver/Grey GIAC, Stainless Headers, GHL Exhaust, EVO intake

when the pressure rises to above 1.4 bar and when it begins to release pressure the pressure should not drop below 1.0 bar. If it does the cap should be replaced.

BTW, a 2-stage cap is referred to and is the preferred cap. (Part # 99.106.447.00 though of course the last 2 digits are now up to at least 02 and some have reported buying a new cap and getting an 03 or even an 04 version.)

And a pressure test of the cooling system should have the coolant system (cold!) pressurized to above 1.3 bar. If the pressure decreases there's a leak. (Of course the cap must be tested first and found good.)

Sincerely,

MarcW.

I replaced the cap last night, and when I got to work this morning, the bleed valve was still closed. After reading a few forums, someone had stated that the caps can fail after the car overheats, which happened when my waterpump went out a few weeks ago.

As far as the cap goes, I decided to try a local alternative. I purchased a Murray from Oreilly auto parts. Part number 7025, for $6.99. It was marked with a VW part number 171 121 321 D. I'll keep a close eye on it for a few weeks to see how it does. So far so good though.

Thanks for the response.

John

2000 Boxster S Arctic Silver/Grey GIAC, Stainless Headers, GHL Exhaust, EVO intake

Minus 40 degrees... Is that Fahrenheit or Celsius?

Interesting- I have been watching my bleeder go up and down on its own for 2 years... I have had no cooling issues even though I beat the piss out of the car.

I am going to put a new cap on and see what happens.