Test's need to be done.



* Possible faults

coolant leak,
coolant temps
Head/block crack,
Headgasket,
Turbo core
Header cap ratings, but if nothing else wrong, wont be a issue



1st off i'd do a

- check for any leaks
- check the coolant system is running at sensible temps, 87-94oC.
- Comp test
- Pressure check each cylinder @ 100+psi for at least 30 mins each, with gauge on coolant system,
- Coolant system pressure test, inc testing the header cap rating.
- take the car for a spin with pressure gauge on coolant, and if it goes above 5psi on normal driving @ normal running temps, and below 15 psi on a little thrash.

=
If coolant pressure dont move on cyclinder press test, then usually the h/g, head and the block is fine.
If coolant pressure jumps up after a/few short blasts, then the h/g, head, block or turbo fault.





Mayo in the oil, dont mean head gasket is gone, nor does it mean it hasn't if not seen.