Smells upon smells from the vents! The dreaded bad heater core, and something else?

lardope

Veteran Member
Joined
Jan 16, 2018
Location
Los Angeles, California
TDI
MKIV
So with the heat running in my car I'm smelling a sickly sweet smell from my vents, something akin to burnt maple syrup. A quick google search informs me this is the dreaded leaking heater core that requires a hellish amount of work dissembling the entire dash from the inside to reach it. Please send your condolences. I honestly would prefer almost any mechanical problem to this.

However, with the heat off and the temp dial all the way to cold (but no AC), I smell something different, a smell I can only describe as slightly vomit-ish. I know another common smell is mold or mildew, but my reference point for mildew is when I wash clothes in a front loading washer and forget about them for a day and then they smell rank. That is not this smell. Any thoughts?

The only time my vents DON'T smell is when I have the AC on and the dial is all the way to cold.
 

Genesis

Top Post Dawg
Joined
Feb 26, 2003
Location
Sevier County TN
TDI
'03 Jetta Wagon
Its the heater core.

They're all in the same box and yes, its a time-consuming job. Its not really that hard, just a serious pain in the beck and you should replace anything that is questionable while you're in there (which might be the whole box assembly) because obviously doing it twice is not something you want to deal with.
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
The sickly-sweet smell is G12/G13 and there's a heater core in your future, but the other smells could well be an aging cabin air filter, maybe even with something growing on it.

Will only take a phillips screwdriver and a couple minutes to check it out... I change mine yearly so as to keep the charcoal at least partly active. :)
 

vdickie

Member
Joined
Nov 8, 2024
Location
Lemoore, CA
TDI
2013 Volkswagen Passat TDI SEL W/ Sunroof - White
Agree with everyone, and the mold smell is probably coming from a wet cabin filter. Sometimes if they get too moist from the AC and ambient humidity, they tend to get a little musty.
 

C.Powell

Well-known member
Joined
Oct 10, 2017
Location
Alberta
TDI
MkVI Golf Station wagon
Also check for rodents making a nest in the cabin air filter. Nice and warm and safe for them but makes the inside smell odd, then weird and then nasty depending on life cycle of rodent and if they die in there.

The smell of the Bounce sheets for tumble dryer use deters them. Leave a pack spread out in the garage and on the floor under the vehicle.
 

golfclub

Well-known member
Joined
Feb 11, 2014
Location
Victoria B.C.
TDI
2000 TDI Golf
I also had this exact situation. When I changed the cabin filter I found a mouse nest on top of it.
I changed the filter but also made small sheet metal pieces to cover the areas between the plastic
cowl and the body where mice could get in. I also installed the seals around the wiper shafts that
were missing. I used to have mice inside the car too. Two winters so far and no mice living in the car..
 
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