The narrow tube that connects the radiatorcap with the expansiontank was totally clogged by a large clod of
hardened radiator leak stop. You know, the one some people use intead of a decent fix.
That way it comes with no surprise the pressure got up so high something needed to break after the thermostat got to opening posistion.
Luckily I found this before I reinstal my 345 Euro renovated radiator later on this week.
![Confused :?](./images/smilies/wacko.gif)
Nowadays radiator repair shops can get hold of bent radiator tube networks, which they can place instead of the one on your broken radiator. The sides get mounted back onto the radiator, leaving you with a virtually new one. Let's hope everything fits and works when it comes back at me this week...