Blocked cats blow engine.
I repaired a 147 2.0TS Selespeed engine which blowed a head gasket after bursting a heaterhose and overheated. It blew the headgasket again after +/- 100km.
Stripping the engine I found the head gasket distorted and blown into the water channel on no 1 cylinder, the weakest point of the gasket. The head and block was still straight so I replaced the gasket & head with new headbolts again. It blew at the same place again within 100 km.
This time however the car came back smoking and with a bad misfire. I stripped the motor again and found the pistons on No 2 & 3 broken between the rings. This pointed to too high compression & after replacing the pistons & reassembling the engine again.
The owner of the car was impatient and I had no time to drive the car on the previous occasions so this time I insisted on driving the car myself.
It was dead...not reving over 3000rpm. Viola!!! blocked cats! I removed the cats by replacing them with a 2001 156 2.0TS branch & a silencer. End of problems!!!! The car is now better than perfect.