like line7 said, sounds like head gasket related issue. does your exhaust smell like coolant?

i say pressure test your coolant system and if it doesnt hold 14.7 psi then you go from there.

you might also want to look at the timing belt side of the cooling system. water pump bolts are very lightly torqued and leaks can start from there too, but you cant see them because they're under the timing belt cover.