back pressure

please can anybody help , have a defender tds 130 , T plate which has a pressure problem . The symtoms are , when vehicle is run at any speed 50 / 55 mph over 12 - 15 miles when stopped there is a bubling noise of air returning to tank which can be herd from insidr , when the bonnet is lifted water / steam is coming from cap on tank . when water level is checked it will take a couyple of litres of water easily , air has been bled from system and a new radiator fitted recently it was in poor state.engine runs finr , sounds great , starts ok etc , just looses water all time . the bubling noise when stopped has always been with vehicle while i have owned it .( 2 years) though not as bad . realise it may be a serious problem just wondered if anybody had any thoughts . all advice apreciated . thanks in advance . jim

1st thing to do: get a coolant sniff test done to see if there is exhaust gasses in with the coolant (Head Gasket Failure) - most garages can do the test cheaply.

Thanks Daz will get that done , theres no water oil contamination but that sounds a better test . cheers j

oil will only show if its a break in the oil/water bit of the gasket, the sniffer is a test for exhaust gases in there (ie break from cylinder to water)

Sounds like head gasket failure, I am guessing being a T plate this is a TD5 (not sure on year changeover), if so then its possible the head has cracked, is a common fault on TD5's...

As above head gasket,
I have been through the same stuff a few years ago. Not cheap but still mortoring 4 years later

Thanks guys for all your help , its going to garage next week , will keep you posted . j

Check the condition of the pressure release spring and the neck seal in your filler cap.