2005 SAAB 9.3 weird heater issues

My daughter has complained about periods of no heat- fan blows but cold air. Next time the heater works fine. She is keeping coolant level up but does need to add a bit (pint or so) say every other month. Last week during the Chicago snow storm she called and told me the heater (which had been working) blew a bunch of “smoke” into the car and onto the windshield and windows which then froze solid. I assume the smoke meant steam and she did say it had a sweet smell when I asked her. Car was towed to a SAAB dealer who ran the car for a couple hours and found no issue and then drove the car for a period with no issue. I had my local mechanic also check it in the past for no heat and it also worked fine then. Only thing I can think of is that there might be a small/intermittent leak in the head gasket with an exhaust bubble forced into the cooling system? That does not explain the steam in the passenger compartment though. Could it? Any thoughts? Thanks!

Sweet smelling smoke from heater vents means coolant and that coolant is getting inside the heater box then blown around by the circulating fan. Or, there is hot vaporized coolant coming off the motor that is being sucked into the fresh air vent when the heater fan is running. Is is important to figure out where the vapor is coming from. Easiest place to start is with the motor running up to normal temperature open the hood and look for smoke and vapor. The fresh air intake is located at the base of the windshield. If you don’t see anything then the problem could be internal inside the heater box which is located inside the passenger compartment.

Either a hole in the heater core (which is in effect a small radiator) or a leaking valve, or leaking hose fitting somewhere in the heater box. The no heat, then heat indicates a problem with the heater also, which may or may not be related to the “smoke”. Some heater cores are easy to access, but many involve removal of lots of stuff sometimes the entire dashboard. I’m not sure what is involved with an '05 Saab 9.3.

This smoke is oily and hard to clean off the windshield since it is vaporized coolant. It will likely return and when coolant is flowing to the heater she will have heat, but she will likely get more smoke as well.

Thanks for the input. Neither mechanic could find any sign of a leak at or around the heater core. We will check under the hood in case it is being sucked in the fresh air vent. No merit to the intermittent gasket leak theory in your opinion?

I don’t see a head gasket issue based on the symptoms given. You can check head gasket integrity with leak down tests, compression checks, and looking for coolant in the oil, and/or oil contaminating the coolant. I won’t say it couldn’t be a head gasket, but it looks like a long shot based on info so far.