Foul smell when heater turned on

The transmission fluid leak could cause a foul smell, IF , somehow, the leak was causing fluid to be burned in the engine compartment somewhere and the smell of burning tranny fluid is getting sucked into your heater vents, behind the firewall. I would use this as a last resort for diagnosis, I dont feel like thats the case here. VW's commonly have problems with the A/C - Heater unit, Vents, Condenser, the whole system. Does it smell anything like engine coolant? If you faintly smell a coolant type smell, or like a burning engine fluid type smell, then you have another heater core problem. Do your windows fog up really easily with the heater on? That is a definate sign of faulty heater core. Remember, VW's Coolant system are under vacuum pressure, so if your technician replaced any coolant, added, or flushed your coolant system after repairing the heater core, and he did not repressurize the cooling system properly, a number of things could malfunction.. including your brand new heater core. You might also want to make sure that if he did replace / flush coolant after the job, that he used VW's specific coolant. Its not the same coolant that standard vehicles use. Hope this helps!

Hi,

Yes, you have helped, thank you. The smell is like antifreeze and plastic, says the mechanic. Should I ask him if he used the right coolant and pressurized the system after putting in the new heater core? I imagine this would be taken as an insult. Like I don't trust he knows what he's doing.

Any thoughts as to if this smell could that the radiator is leaking? At this point, I don't know if I should just take my car to VW and cut my losses with this independent shop ($800 loss).

Please advise.

Thanks again.

Well you should start by looking at the coolant reservoir. If the coolant is orangish-pinkish, then its the right coolant. If so, then go ahead and ask if he knows that the VW coolant system is pressurized. alot of mechanics, amazingly, treat it like any other car, and its very different. Ask him with a smile though, kinda more informative, than insulting. Dont wanna piss the guy off. You can look at his reaction when he replies to see if hes lying or not, people dont like to admit that you know something they dont. Then, after he replies ask him how he pressurized it. That will be a dead giveaway. Respectively, you could also ask what tools he used to diagnose the car, VAG-COM or OBD-II, or both. Dont tell him the answers though, let him tell you. if he doesnt answer correctly, then I would tell him that his services would no longer be needed. If hes a good mechanic he will answer correctly, and you could have him double check the heater core. What about the windows fogging up? Glad to be of some help. :)

I don't think there's any fogging. And the foul smell is on and off. It's strongest when I first start the car and turn the heater on. That first whiff of air always smells bad. Then it goes away. A little later it comes back. There is no smell at all if I keep my thermos on cold.

Did I mention that the mechanic did a "pressure test" a few weeks after he put in a new heater core? The test revealed no leakage. So he returned the car to me saying there's no leak -- even though the smell persists.

The whole reason I took my car into the mechanic a month ago in the first place was that foul smell. And it is still not resolved.

Are those pressure tests 100% accurate? Is it worth repeating?

Thanks for your advice.

Well in that case, my only theorys are either he overpressurized the coolant system, or you have a head gasket leak or a blown head gasket, and coolant is burning on the inside of your engine. Tell the mechanic to change your oil, and when he drains the oil, check to see if there is remains of coolant; also look where you fill your oil. You might notice the smell that comes out might smell like what your are smelling in the car. If thats the case, have your intake manifold and your head gaskets checked immediately for leaks and cracks. Hope this helps!