'04 Subaru Legacy Wagon smells when sitting still

I live in central Wisconsin and have a 2004 Subaru Legacy Wagon with around 90,000 miles on it. I purchased the car in 2008 with about 26,000 miles on it. Starting two years ago, whenever the air temperature is below 15-20 degrees, my car will develop a smell of antifreeze in the cabin when I start it and let it warm up for a minute or two. It did not do it for the first winters I owned it. I have not been able to detect the smell outside of the vehicle, and I have not been able to detect the smell in the summer months, even if the car is left idling for several minutes. The White Whale (my cars name according to my wife) was worked on by my local mechanic (where the car was purchased) last winter. They considered and replaced the thermostat, a leaking (or at least they thought it was possibly leaking) hose, and then finally after consulting over the phone with the Subaru dealer that is a little over 45 miles from my house, decided that the problem was likely the head gasket. So at around 65,000 miles I had the head gasket replaced by the Subaru dealer. Problem is, they replaced it in March, and the temps were high enough that I couldn’t really tell if the fix had fixed the original problem or not. It had seemed that the smell was at least less intense, but hard to tell. So, here we are in the midst of January, yesterday the car started beautifully (which is one reason that I love this car) after sitting outside all night at -11 degrees Fahrenheit with wind chills down to below -30. Last winter, in these conditions, the smell would be so strong that I would get nauseated driving the entire 15 minutes to work. This winter, since the repair, the smell seems limited to only the first idling time. After that, the cabin seems to get cleared out with fresh air, and the smell dissipates. There have never been any check engine lights, the oil and coolant levels have never been a problem, the temperature is never higher than just above the mid-line on the gauge which has stayed the same all throughout the time I’ve owned it, and performance has been completely unaffected by the smell, other than my performance as a driver when trying to navigate in a car that reeks of antifreeze. Also, I have never noticed what some describe as a haze or liquid building up on the windshield when a heater core goes out and my mechanics, both dealership and local, assured me that this was not the problem. Any thoughts?

The only place antifreeze is present in the cabin is the heater core. And, with the heat on, any leak will be very noticable. It is possible for the smell to be sucked in the vent system from outside thru the windshield vent, but this possibility can be eliminated by using the recirculate button on the heater controls.

Are the floors wet? Get a plain white paper towel or rag, press it around the floorboards under the dash, and see if it pulls up any liquid the same color as your antifreeze. I mention this, because if the leak is at a seal or line just outside of the core, the steam from the leak may not rise up through the defrost vents.

I’ll try the recirculate button and checking the floors when I leave this morning, though I have never noticed the floors being wet before.

I believe that your mechanics are wrong. You have a small leak in your heater core. The smell and the haze on the windshield are both red flags screaming “leaking heater core.”

There is a smell, but no haze. I thought heater core right away myself, but have been assured that this is not it. Round 2 of battling it out with the dealership?

Also, if it were the heater core, wouldn’t it continue to smell throughout my drive?

Depends on the nature of the leak. Yours appears to reseal when hot enough, so the leak would stop for most of the drive.

@drgosse you have the CLASSIC symptoms of a bad heater core.
I am very surprised that your mechanic and the dealer don’t agree with this.
Have one of them replace your heater core, against their advice if need be.
If that heater core fails catastrophically, your engine is in big trouble.

He said he doesn’t have windshield haze. I would try a small can of non heavy duty stop leak in the cooling system.

Okay, I paid closer attention this morning. I let the car idle in the driveway for 5 minutes, and set the ventilation system to recirculate the cabin air, which I never do otherwise, with the fan on high and VOILA! no smell in the cabin. As I brushed snow off the windshield I think I did smell a hint of coolant, but I’m not really sure. Still, no clear indication of a leak. No puddles and no low levels of coolant. Does that rule out the heater core if it did not smell when it was drawing air from the cabin instead of outside? Seriously puzzled with this.

Yes. The heater core is not your problem. Tomorrow morning, lift the hood before you start the car, and immediately inspect the engine before and after you start it. Concentrate your attention to any coolant lines, especially the small ones to the throttle body and edges of the intake for visible coolant leaks. Particularly the back of the engine.

Will do.

The heater core IS the problem, IMO. If you smelled coolant in the cabin, the heater core is a goner. A bad heater core won’t always leave huge puddles in the cabin.

So, a little more information. I have, since my last posts, had my car serviced and assessed by trusted mechanics other than those that had seen it before. After inspection and driving, they cannot determine the location of the leak. All of them have agreed that it is not the heater core, and none of them have been able to locate any leak or residue around hoses or the head gasket. One mechanic found a small amount of dry residue on the top of the radiator, but did not think that that was really enough to be causing the problem. They all agree the smell is definitely in the engine compartment. They all recommend that I continue to drive it. Coolant levels show no sign of going down. Performance is not affected, and temperature gauge does not show any problems. I have resigned myself to driving this thing with the coolant smell flooding into the cabin. I’m thinking about replacing the heater core simply because no one can come up with a better explanation, even though no one that has looked at it believes that it is the core. Advice?

Have dye added to the system and have it pressure tested. You can see the leak with a black light. It could be the water pump weep hole and it would not show up normally. It could be dripping in the timing cover.