I bought a van that was owned by a Indian or some middle eastern dude... they cook with this reaky oil called gia or something,,,I know cause I once maintained an apartment complex where they kept reusing this oil for months,,,it was ranky... Well the van smelt like it every time I turned on the heater... I finally got rid of the smell by every once in a while pouring a couple shotz of whisky into the vents... So maybe your smell is in the vent piping...