Gary.pb wrote: a small crack on the header tank which appears to be letting in/out a small amount of air. According to the brick yard guide the system is pressurised. Is this what would have caused the problem in the 1st place??? It is not leaking water but you can see bubbles indicating that air is getting in/out.
Hi Gary, as you may know, when the motor gets up to temp, the header tank is supposed to vent the extra volume of coolant created by expansion into the top up tank via the pipe on the dalek cap. Then when the motor cools, the coolant contracts and the vacuum ("suction") caused sucks that coolant back from the top up tank into the header tank.
Now, if you have a leak anywhere on a WBX coolant system, it is likely that that will be the easiest route for that suction to access, so instead of sucking the coolant back in from the top up tank, it can suck air in instead (from the area of the leak). In this situation, every time you turn the engine off and let it cool, you are sucking more air in = not good.
I would be changing that cracked expansion tank and get a new dalek cap whilst you are at it, just to be on the safe side. Don't buy these parts from GSF or JK, as often said on here, Brickwerks can be relied upon to provide top quality parts.