The head is either cracked or warped, the mechaniics should have checked the head for any indications of warpage. It is also possible a headbolt is stripped.
In any case you want to get this repaired ASAP, if coolant gets into the oil you are looking at damage to the main bearings and coolant will kill an O2 sensor very quickly.
Take it back to the garage that originally did the work and simply tell them it is was not repaired properly.
You may need a new head, or you may find a good used one at a junkyard.
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Tuesday, August 5th, 2008 AT 5:27 AM