RRC Coolant loss

[Jsbholden]

I'm loosing a small amount of coolant from the coolant bottle (have to top up every 200 miles or so). After a run and the vehicle is parked up you can hear a hissing from the bottle cap, with signs of coolant running down the sides. there is no oil/water mix or clouds of white smoke from the exhuast, the heater works fine with no smell of antifreeze so i think that prob rules out the head gasket or heater matrix. could it be a duff tank/cap??

btw, its a 3.9 auto

 

[Jsbholden]

changed the header cap which has stoped the coolant leaking down the side of the tank but still using about a pint of coolant a day. started to get lumpy on idle (when warm) so i now think it is the headgasket(s) (with mayo in flametrap breather hose )

any idea of how i much i should expect to pay to get these changed?