Burning smell when heat is on

Car: 2013 Hyundai Santa Fe
Location: Atlanta, GA
Problem: We have a sweet burning smell like antifreeze or oil coming from the vents when the heat is on. We have taken it to 3 mechanics and they can’t figure out what it is. We expect the heater core is going bad, but the symptoms do not fully match what we are experiencing. We do not have any leaking antifreeze, nor do we have any windows fogging. They also ran a pressure test which came back normal.

Any thoughts? Thanks for your help!

@Logan Steele
Does This Vehicle Have A Cabin Air Filter? If So, Has It Been Changed/Checked Recently?
I’m wondering if it smells? I’d access it using instructions in the Car’s Owner’s Manual, look it over for any unusual stuff on it and give it a whiff. Some can develop a “dirty sock” smell or have microscopic vegetation or fungus growth, mouse debris, etcetera.


Another possibility is debris (leaves, seeds, etcetera) in the blower fan wheel restricting it and causing excessive heat or in the air duct housing the blower resistor, which gets very hot.

A small coolant leak either due to a faulty heater core or – more likely – a faulty connector could cause this. There’d be no signs of coolant or foggy windows if the leak was small enough, it would just all evaporate. You’ve already lifted up the carpet to make sure it isn’t wet underneath, right? Also you could be noticing a small coolant leak that is occurring in the engine compartment. The odor will be sucked into the passenger compartment via the vents under the windshield, definitely this will happen if using fresh-air mode. Good idea to open the hood to determine if there’s an odor in the engine compartment at the end of a long-ish drive.