How long can a heater core leak?

I have a 2001 Lincoln Towncar (178,000 miles) with a heater core leak. I was on the highway and got some smoke out of the ac vents and ever since then I’ve smelled the sweet smell of coolant in the air coming from the AC. I haven’t had any more smoke or vapor since the one time. I did my research and asked around and understand this to be the tell tale signs of a heater core leak and that it’s one of those fun jobs that’s going to be a high price tag at the shop because of the amount of labor (8-9 hours).

Since the dash has to come out, I thought it would be worth it to pay a little more and have a dealer do it since they’d be more accustomed to taking out and reinstalling that particular dash. So I describe the problem to the dealer over the phone and they want to diagnose it before giving me a quote on replacing the heater core. Why? No clue, I even asked the guy if there was any other possible way for coolant to get into the vents and he said not that he could think of.

Anyway, I took it into the dealer and low and behold they found a different coolant leak. It turns out for a while Ford used intake manifolds with a plastic part that is known to crack and leak coolant. The dealer wanted $1500 to replace the intake manifold and clear the condenser drain before we even got into the $1200 for the heater core. So no way was I going to shell out $3k on my 2001 even though it’s in great shape otherwise.

So here’s where I get to my question. I ordered an intake manifold and replaced that myself, I still haven’t addressed the heater core. The first puff of smoke and the coolant smell happened almost 5 months ago. I’ve been driving around with antifreeze in my trunk and my eye glued to the temp gauge and it has not budged at all. I started thinking if I could get through the winter months I’d just bypass the heater core and buy myself another 7-8 months where I don’t need the heater and I could save up some cash to have a pro replace the heater core.

Now that the warmer weather is here, I’m left wondering–could the heater core really leak for 5 months without me ever having to add coolant and with the temp gauge never going above it’s normal level?

Why not pressure test the heater core before deciding?

As to how long one can leak, the answer is “until it’s fixed”.

It is possible that the smoke from the vents was caused by the intake manifold leak hitting the exhaust manifold and being drawn in. It is also possible that there is some stop leak in the car that has sealed up the heater car. Some manufacturers put it in at the factory. I know that Cadillac has done that.
I have used stop leak to seal up a heater core and had it last for years. I just wouldn’t use a heavy duty one like Bars Leak. I used Dupont one time and Aluimaseal another. If it plugs up your heater core, well it needed replacing anyway but I wouldn’t put it in unless you have fresh evidence of it leaking.

Was the carpet wet?

Has the windshield fogged up, with sticky residue?

The carpet on the passenger side has been wet twice that I’ve noticed. That’s what the dealer cited for needing to clear that drain.

I haven’t had any fogging on the windshield or residue. I’ve been looking for it but none to date, just the smell.

Usually you will get that sweet smell that won’t go away and the windows will fog and will not clear. Have you lost any fluid?

Usually you will get that sweet smell that won't go away and the windows will fog and will not clear. Have you lost any fluid?

This is why this seems strange to me-- I have the sweet smell, although I would say it has diminished in intensity but I haven’t had any window fogging at all.

I don’t think I’ve lost any fluid since the temp has remained steady for five months. I keep looking at the reservoir but for some reason it’s not very opaque and it’s hard to see the level and the radiator cap has been a royal pain to get off.

I got the car a few months before this happened. I wonder if there could have been an existing heater core leak and the previous owner used stop leak.

For an '01 I would try a stop leak (Justice Brothers makes a good one) if it happens again. Have used it twice before myself with good results for heater cores myself.

Fix the intake manifold first, then retest for the heater core. My 2000 Explorer has a plastic lower thermostat housing. It cracked and began to leak. I could smell the coolant through the vents as I drove. I also thought it was the heater core. But, it took over a year before the crack that seeped coolant opened up to a full blown leak that I had to fix. Once I fixed it, the smell went away. Heater core is fine and coolant is no longer disappearing. I had a bad heater core in my Toyota, and it left a nasty white film on my windshield. If the windshield is clean and the floors are dry, it’s probably just the intake manifold.

Just my experience but I was 5 miles away at NAPA checking on a radiator and the car must have over heated a little on the way home but by the time I pulled into the garage the cockpit was filled with steam like a steam bath. It wasn’t going anywhere. I don’t think I had a problem before but when it decided to go it went fast with little warning. I’ve had a couple heater cores go though and usually it was just the leak on the floor and the residue on the windshield. So the answer is who knows? You can always block it off in the summer.

Again, the old joke about the beginning of the Ford assembly line with only a heater core hanging from a hook. Then, the rest of the car is built around it…

Make me long for my old Chrysler products. My early ones, the heater cores were under the hood along the top of the passenger inner fender and all the Valiants and Darts in the family had the heater core hanging from one bolt under the glovebox.

My understanding is that it’s not particularly healthy to breathe in coolant fumes, so that’s one consideration if you can still smell the coolant inside.

I don’t think your heater core ever leaked. I suspect that the leak from the intake manifold created fumes under the hood that got sucked into the air intake of your hvac system when it was on outside air. The intake is located under the cowling just forward of your windshield.

Do not bypass your heater core. Heater cores are used as an integral part of the heating system and reduces fluctuations in the engine temperature caused by the opening and closing of the thermostat.

My recommendation, leave it alone and just do the recommended coolant changes with the correct type of coolant as called for in your owners manual.

How long can a heater core leak?

Until it’s empty!!!

I’ve avoided doing that for three days…I couldn’t resist any longer.


Update: At this point I am convinced the heater core was not the culprit. The upper radiator hose burst about a week ago, spraying coolant absolutely everywhere inside the engine compartment. I could smell coolant in the vents for about three days afterwards as all the ejected coolant burned off the engine, but never had any vapor/smoke or fogging on the windshield. So I think Keith’s theory is correct and I’m moving on (but with a jug of 50-50 in the trunk and an eye on the temp gauge).

Thanks for letting us know you got it fixed. Transient smells come from under the hood. A heater core will continue to stink and usually soak the carpet when it gets bad enough. I applaud the dealer for not soaking you on a heater core.

Whenever I have a leak or spilled antifreeze under the hood I flush it away with water, otherwise the smell persists and it is hard to tell if it is still leaking because antifreeze just doesn’t want to evaporate.

I have a friend who has a '96 Civic and the heater core AND head gasket have been leaking for almost 3 years. He only drives it 2 miles to work and then picks up his work truck. I’ve suggested fixing the problems and he feels it’s easier to just add coolant. It doesn’t leak a lot, I suppose. Rocketman