Exploding expansion tank x2

[paul463]

My 2013 XKR, had sudden temperature rise then it dropped as quick, then fine but I took to garage and had thermostat changed and checked that fans were working. Half a dozen trips later the temp shot up, I pulled over and the expansion tank bottom blew out.
Recovered back to garage, new tank fitted all was good or so we thought but when they had it back two week later for MOT the tank exploded again during emissions test.
Garage has been told the material the tanks are made from age and this could be the fault, then people switch to alloy tanks. But I am concerned there is another issue with the cooling system.
Any ideas?

[Astromorg]

Two thoughts; first, I would think that a new tank came with a new pressure relief cap, but if not and the old cap was re-used, it might be faulty and not relieving excess pressure.
Second and more likely is that the tank was over-filled and couldn't relieve the coolant expansion fast enough. The X150 models have no atmospheric tank to take and feed back excess coolant. They depend on a significant air space being left in the top of the tank. The max level is marked on the tank but can be overlooked.

[paul463]

Thanks it was a new cap.
I’ll make a point on the water level.

[paul463]

Thanks it was a new cap.
I’ll make a point on the water level.