[walker]

I would remove the heater hoses and check out the inlet outlet barbs. Then flush out the core through the hoses with a garden hose. May as well replace the hoses while you got 'em off too. Odds are there is a piece of gasket or sealant blocking one of the hoses or fittings. Make sure you have the hoses routed so the you have one routed to a port on the outlet side of the water pump (engine side) and one on the return side( on the pump at the lower hose or to the radiator), as it takes pressure differential to circulate water. Also, make sure your air is circulating through the right ducts, as outside air intake dilutes your heat. I think the vaccum operated duct on the P/S of the engine compartment is apt to fail and leave you sucking outside air.
There is also the possibility that your t-stat is stuck open not allowing your system to heat up.
Oh, and if you think you still have oil in there you may consider mixing some simple green in plain water to emulsify the oil. Mild mix should do it, but I don't think that is your problem.