coolant cap hising ???

flushed out my coolant in my top fill rad filled up ok ran it with cap off to get rid of air bubbles etc heater on hot and full blast and after letting fan kick in put cap on then was gonna wait to let it cool down but i could hear a hissing sound coming from the cap, does this mean the cap is kaput ! infact should i just buy one incase cant be too exspensive ?? has the following info on the cap itself - no. 171121 321C  BPO238 cheers all ! noticed that coolant temp gauge needle sat at 3/4 mark bit too hot i think and this was even when driving along ! is that ok also ?

anyone got any ideas ? gonna use a proper coolant flush no as well !cheers

Coolant caps can wear fom age or being overtightened, the hissing sounds like yours needs replacing. Not sure ifyou can still get them from VW, but Euro Carparts and German & Swedish do them for a couple of quid. Car's temp does sound a bit high, it usually should sit around halfway, replace the cap before worrying about this though as a faulty cap can cause this ort of problem.

Cheers

Cheers for reply ones on the way cheers Mark !!