Seems all heater cores go in time, you should notice your coolant level going down, when mine went I found if I switched the temperature control to cold it stopped/reduced the leak while I waited for the part :cheesy:
Don't Panic! Yet. Look for coolant drops on the passenger side floormat, constant 'misting' on the windshield (also passenger side...or film left when a fluid dries on the glass...you will know it), and/or significant coolant dripping under the car. Those are the 'FIX ME NOW" symptoms. Every now and then I get the coolant smell, then it goes away for months. This usually happens when seasons change and temps make a big swing. Last week we went from 60's to 90's and I had the smell for a day. Still in the 90's, no smell. Heater works fine and coolant level is constant. My best guess is with age there is some seepage around the fittings or in the hoses. Someday I will have to replace the heater core, et al, but just not yet. Depends on how badly corroded yours is.
Also, DO NOT USE RADIATOR LEAK SEALER!!!! If you do you will be replacing a lot more than the heater core. If you do decide to replace it, check local radiator shops. They may be able to fix your core which is a lot cheaper than replacing it.
No radiator sealer? I use bar's leaks... because of stuff I read online. How bogus... I just put a bottle in last night. Some dude has a website devoted to the stuff. What gives? Bar's Leaks or no Bar's Leaks.
I agree, try Bar's Leaks as indicated in another of my posts.
It CANNOT harm your cooling system and anyone who suggests it can doesn't know how the stuff works. It is a vegetable fiber suspended in a water pump lubricant, basically.
Also, the standard heater core uses bayonet style heater hoses that just plug into the heater core pipes and are sealed by o rings. My idea is that some movement occurs in these joints causing seepage before the o rings re-seal. Bars Leaks seems to stop the coolant smell type of heater core seepage. No leak blocker can handle a hole big enough to leak significantly, it just can't hold the pressure.
Bottom line: try Bars Leaks as you have everything to gain and nothing to lose. If it doesn't work, try replacing the heater hoses using new o rings and white petroleum jelly (vaseline) to lube the o rings when you insert the new hoses. Only then assume you have a failed heater core. Generally, a failed heater core will dump a fiar amount of coolant into the car or onto the ground depending on where it is leaking.