water probs

[bobbymk11]

right been to glasgow and back today....and noticed water preasure is pushing water so high that its comming out over flow....when i got back to perth....i let it cool down and opend up cap....let it run and heat up again with cap off...and once running at right tempature..topped back up to between min-max level...let it run for another 10 minutes or so....and rev'd car up when i do this its level goes well over max mark ...and after doing this a few times as car got hotter rev it up and comes right over the top...then settles back down below min mark....once at this level will stay there and hold its water???

im lost....tried everything as to what it might be....had compression test done last week and was all good....No return of white mayo on oil car...No oil in water...no white smoke from exhaust...and car runs perfect...No loss of power...Tempature gauge is fine..oil temp is fine...??

what on gods earth is the cause of this... as costing me a fortune on vag coolant 

p.s. if car holds water and runs fine with level below min is it ok to drive like this...

[Leon R]

Change the cap first. If its black its known to go wrong as there is a blue replacement one you probably need.

They are cheap but normally you should carry out a pressure test on the cap to see if it holds pressure to a certain bar then releases. Yours may be releasing too low.

[Simon8v91]

^ Agree - change your cap first 

Is you bottom radiator pipe getting warm once the car is up to temp? If not this may indicate an air lock or thermostat not pinging open.

To shift an air lock is easy - run up to temp at idle with expansion cap off.  Hold revs at 2500 - 3000 for 20 - 30 secs and then return to idle and switch off.  Water will boil over, top up and refit cap - job done! 

[bobbymk11]

have new blue cap on car....and pipes top and bottom both get warm ...and go solid....think maybe air lock somewhere??? not sure....will have to drain system and give a good flush and try again i think....

cheers for info lads