on the alloy water tanks that ggr do,there is a pressure valve fitted to the top right connection,like a tyre valve, why?

 

Not really a necessity on a road car, but on the rally cars, If they depressurised the coolant during "service" they would re-pressurise to keep temps down as quick as poss before heading off

 

oops read that wrong!

 

good one damo

 

Higher pressure raises the temperature that the water boils at.... some systems have a schreader valve to pressurise the system..

 

Which is what I said

Which is what he asked about

 

nearly!
the pressurisation does not reduce the temp- it just stops the water from actually boiling.

 

the systems are pressurised to 2 bar all the time....to increase boiling point.....

 

what is the benifit of higher water temps as all the newer cars have higher boiling points these days

 

there is no benefit to higher water temps- you would only use this system in a situation where you can not cool the water down sufficiently.
Pressurising the system will allow you to run at say 115 degrees C without the water boiling and spitting out everywhere...

 

You know what I meant