Do a combustion leak detector to see if there is a blown head gasket.

See this Lisle 75500 Combustion Leak Detector

Checks for combustion leaks caused by bad head gaskets, cracked blocks, and cracked or warped heads. Fluid changes from blue to yellow when exposed to combustion gases from the radiator.

http://www.jbtoolsales.com/.../

Local auto parts stores such as Autozone or O'Reilly have a free loan tool proram ( a small deposit will be required ).