Expansion tank problems

I have change 3 expansion tank，but now the newones seem crack again，the garage said because the enginen pressure，please give me some advise how can i do with the expansion tank？

I'v got a pre 2000 tank on mine. I've been through 2 modern tanks. The older style don't seem to split.

The new ones seem very week，i should find the method to stop it crack

A new one does not necessary mean the new model. The new model has thicker threads. Is that what you changed to?

Petrol engine?

yes, it is perto engine,i already got a new tank and change to use all coolent ，now seems ok，no more crack. i will contiune check it . thank you !

did you change the cap each time too ?

Surely the expansion tank cap is the "Safety Valve" for the cooling system and should relieve any excess pressure over and above what the system is designed to work at ????
Even on old motors, where the filler cap was mounted on top of the radiator, it was spring loaded in order to lift and relieve the excess pressure through the overflow hose rather than explode the radiator. The caps were stamped with the relief pressure dependent on the engine/model .
I feel sure that the expansion tank cap is designed to relieve any excess pressure, rather
than let the plastic tank take the strain and blow.

that's why I was wondering if he changed the cap each time too. If it fails to release at a certain pressure, it will over stress the header tank

Mine has done the same. been through 2 new tank + caps.
the company blamed me for it breaking. The actual reason i found is that it fouls on the bonnet when it is shut..... Not fixed mine yet

yes,but the last time i did not change the cap,because i think it seems like new