Without success, I replaced:
Fan clutch
Thermostat (180 deg just to rule it out)
Water pump
Rad hoses
Heater hoses
Coolant (it is perfectly clean now)
ECT sensor
Radiator cap
Parts that are good:
Fan shroud
Electronic fan (switches on about 218 it seems)
Tests that were done:
Radiator pressure test (16 psi) - Passed
Radiator backflush - Clear
Thermostat test - Hoses are hot
Fan clutch resistance - Stiff (good)
Block test (engine cold) - Passed
Compression test (engine cold) - Passed
Block test (engine hot) -
FAILED
Compression test (engine hot) - not completed yet
See below for the failed block test, it only failed this test once the engine was clearly overheating/boiling over. (F!*%$ing sucked to test it while it's blowing boiling water at you). Nevertheless, see how the fluid clearly has turned yellow, indicating there was exhaust in the coolant:
One theory is that once the engine gets really hot, the metal warps slightly and opens either a crack or head gasket into the coolant. This isn't a 100% confirmation, but I saw one other post identical to yours on a forum and he said it was a cracked head (but that was an 0331 head, unlike ours).
A hot compression test is something I will try next, but haven't done it yet.
PLEASE DO THE TESTS BEFORE SWAPPING PARTS, optimism will NOT solve a blown head gasket.