2004 BMW X3 3.0i- heater only hot when I drive and it smells, no smell with AC, HELP!

[jokerpalooza]

Hello everyone, I have an issue with my 2004 X3. The heater only works when I am driving and it smells bad through the vents but only when the heater is on. The AC smells fine and works great. The heater blows cold air only and blows hard at the highest settings. What can be the problem? Also, I get a low coolant light that comes on and off as I drive. Could I have an expansion tank leak? Sensor is broken? How does this all tie into the heater not blowing hot air in idle, only when driving, and the nasty smell through the vents only when the heater is on? And is it a pretty expensive fix at the mechanic or is it DIY possible and cheaper. Thanks ahead of time people.

[bmwdirtracer]

While the particular issues you mention could be several different items having failed, you really need to do a complete refurbish of the cooling system. This is necessary about every 8 years on a BMW, so you're well past due. Radiator, expansion tank, plastic water manifold, the two plastic pipes under the manifold, all hoses, and the sensor in the lower hose, plus the fan clutch, the water pump, and the thermostat. In your case, you need to have the heater valve checked, as well as the auxiliary water pump, too.

If your engine overheats, it will very likely warp the head, and pull the threads out of the engine block.

As for the smell, the valve cover gasket is likely leaking oil onto the exhaust.