I have the unmistakable smell of antifreeze (coolant) when I turn on my air conditioning system.
- 1995 850 Turbo, 148,000 miles, Automatic Climate Control

I added UV dye to my coolant reservoir and let it work its way through the system over several days. Using a black light I was able to discover a leak from my water pump. I wanted to make sure my heater core was not also leaking so I took out the center console to get access to the heater core. I opened up the heater core case which gave me about a half an inch to peek inside to see the heater core. I used a black light and could not detect any leak at all. There was no sign of coolant on the heater core or at the bottom of the heater core case. I even checked the heater hose pipe connections on both sides of the firewall with the black light and I saw no signs of leaks.

So I then replaced all of the following:
Coolant reservoir cap
Upper and lower radiator hoses and clamps
Coolant reservoir hoses and clamps
Water pump and gasket

I refilled the system with new coolant and UV dye.

I have checked the entire engine bay thoroughly and cannot find any trace of a coolant leak. So my new water pump installation and new radiator hoses are not leaking. There is absolutely no smell of coolant anywhere inside the engine bay.

But unfortunately, when I turn on the A/C I get a blast of the sweet smell of antifreeze. It subsides after about 30 seconds. If I have the auto climate control temperature control set to the coldest setting (no heat at all) then I don’t get any smell of coolant. But if I have it anywhere else on the dial (i.e., 72ºF or hotter) then I get the smell of coolant. I have run the A/C on high heat for 30 minutes a day for the last 5 days thinking I might need to blow out some residual smell. But I don’t think it’s residual coolant smell in the system since the smell is strong when I first turn on the system then subsides to almost bearable after 30 seconds to a minute.

There are no signs of coolant under the car after it sits overnight.

I have not had to add any additional coolant over the last week of driving about 25 miles per day.

Does anyone have any ideas on what’s causing this coolant smell to come through my A/C ducts?

Is it possible or likely that my heater core is actually failing and that the leak from the heater core is so small that I there is no sign of a leak when I look inside the heater core case?


I’d appreciate anyone’s input.

Thanks!

 

I would recheck the heater core. I recently replaced mine and after pulling it out I noticed the firewall side (not visable unless you remove the core) had a very tiny leak somewhere, I saw a little corrosion but not the actual leak, It was also the reason I smelled coolant even though I had no moisture in the box, it doesn't take much. The Heater core is a breeze to replace. You only need to pull the carpet away in both footwells, take off both sides of the heater box, and the heater core can be manipulated out just by pulling and wiggling it, then do the reverse for the new one. I searched it on this forum and learned how. Do a search for better instructions.

 

That's exactly what I needed to hear. Knowing that this type of tiny failure in the heater core has happened to someone's 850else gives me more confidence in my decision to go ahead an purchase the new heater core. Thank you for your input!

 

Well, I'm happy to report that I changed my heater core this weekend and it solved my problem. (Just in time for winter!)

I did find residue on the old heater core where the coolant was leaking. It must have been a tiny pin hole, not large enough to get anything wet, but enough to create the odor of antifreeze in the vents.

Thanks for all the suggestions!

 

Congrats