Coolant Fumes '98 Outback - recently replaced heater core

I hope I’ve put in all relevant info. Please ask if I’ve left anything out. I appreciate any advice you can provide. Thanks!

Car: 1998 Subaru Outback Legacy 2.5 litre


Coolant fumes (sweet almond smell) in car (via air vent).

Until recently, this only happened when the heat was on.

As of this morning, the fumes are coming in even when the A/C is on (and when the air is turned off completely)

Some things that have been done in addition to regualr maintenance:

Replaced head gasket

Engine replacement around 102,000 mi

Relevant (I think) info:

156k mi Jan 2005: leaking coolant inside vehicle, smelled coolant through vents: Replaced heater core

171k Jan 2006 smelled coolant again: Fixed leaking heater hoses

177k Sept 2006 smelled coolant, interior glass fogged up, mech “added conditioner to coolant, re-secured hoses”

205k Jan 2009: Smelled coolant, interior windows fogged up when heat on: Replaced heater core assy and heater core

207k Nov 2009: smelled coolant, foggy windows: Mech found gross sludgy mud in radiator: Flush/fill radiator & coolant system, tightened clamps.

I really respect the last mechanic we saw and spoke to him by phone today. We moved away from him so need a new mechanic. He suggested we may have old gunk in the system (like someone added a stop-leak at some point). He said to:

1) look in radiator before starting to see if it’s gunky

2) have it VERY thoroughly flushed

3) check all hoses and clamps for leaky spots

4) it’s possible old gunk could have plugged this new heater core

THE QUESTION: Do you agree, disagree or have a different idea as to what the problem could be? Any additional info would be very welcome. My husband always does what the mechanics tell him is the very best thing to do, so I am sure it was well-maintained up to now, assuming his mechanics were any good.

We’re very tired of having this same issue pop up again and again and are considering replacing this car if we can’t fix these issues.

Thanks in advance!

12 year old, 210K mile Subaru’s are getting near, or have long past, their normal service lives…Yours has turned into a money pit, it needs it’s second timing belt and water pump, plus an unresolved coolant leak / smell…

For 50 years, mechanics have been using a simple hand-held pressure pump to pressurize cooling systems and locate leaks. If you are going to continue on with this, I would find a mechanic who is COMFORTABLE doing heater cores and have him replace yours again (if it’s determined it’s leaking) WITH A SUBARU FACTORY PART…There is a lot of “aftermarket” and “rebuilt” junk out there…it is quite possible your “new” heater core was damaged during installation as this can be a very difficult job. The possibility exists it was NEVER replaced, the “gunk” in your radiator the residue of the “Bars-Leaks” sealer that was used to cure the first heater-core failure…

Thanks for the advice Caddyman. How do you know it needs a timing belt? Also, it’s engine was replaced so I think it could live a lot longer -

It is possible the new heater core was damaged during install, but I would disagree that aftermarket parts are always bad. Many manufacturers don’t make all their own parts - At least that’s what some of the mechanics tell me.

I’d like to emphasize the question I had before:
Do you agree, disagree or have a different idea as to what the problem could be? Additional info would be very welcome.