Smells when heating is turned on

[pdu]

1990 318i - When I turn the heating on or open any of the vents I get smell, not sure if its petrol/oil or exhaust fumes, any ideas? what should I check? it's especially bad when I'm stopped or at low speeds

[Andy_magic]

When the engine is warmed up, stop it and gently take the expansion tank cap off and smell it, if thats the smell your getting it could be a leaking heater matrix or the valve near it.

HTH