depending on how many miles are on your car, you may be looking at head gasket problems.
http://www.cygnusx1.net/Supra/Librar...aspx?S=EM&P=18
check under your oil cap for milky oil. and check your rad for oil, and get a compression check:
http://www.cygnusx1.net/Supra/Librar...Section=EM&P=6
if you are under 128 psi in any cylinders it needs replacing, and if any cylinders psi differ over 14 psi it also needs replacing.
beware of a cracked cylinder head. its happened to me.