I'm guessin its the intake manifold gasket or the head gasket, a while ago i thought my intake manifold gasket was leaking but i wasnt quiet sure and i never investigated it any further. But since the coolant is turning brown as soon as i put it in im pretty sure that would be a head gasket. Also i changed my thermostat and there was a oil like substance just sittin by where the top hoes goes into the engine. Also when i goto high rpms, i can smell i guess oil burning off... but it dosnt really smoke.