Exactly a year ago, an indie radiator shop replaced a leaky heater core. I supplied the new core, made in central Europe, with "lifetime warranty" (about $40), as recommended by a few on the Brickboard. It worked fine through a cold winter. (I also warmed up a few times during the summer just to check.)

Now, when I demand heat, a noxious smell blows through the vents. It doesn't seem quite as "sweet" as antifreeze. The smell is somewhat heavier, and maybe a bit burnt.

[Recent repair history: new water pump (with timing belt replacement) two months ago.]

I returned to the radiator shop and they put some UV dye into the coolant reservoir and instructed me to return in a week. I did do and they looked under the hood–but not in the cabin– and saw no trace of a leak. Further, the fellow says that he smells nothing.

I had to return for yet another visit so his under-dash man could inspect around the core and remove it if necessary.

This time I was given the news that there was a small leak in the year-old core.

I had them replace the core with a new one supplied by them.

Driving the car back home (with my wallet $240 lighter), the same smell is emanating from the vents. The higher I set the thermostats, the more it stinks.

I have not noticed the smell under the hood.

The wisdom of knowledgeable Brickboarders is earnestly solicited!

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Thanks to all for help--But problem not solved. After more than two winter months of no heat, I finally went to a "thinking" indie mechanic, who was as intrigued by the strange odor as I was troubled by it. He changed the admittedly filthy cabin air filter and sprayed a lot of strongly perfumed Wynn's AC/heater bactericide/mildecide into the fresh air inlet, but he could find no obvious visible cause for the acrid noxious menace. After some of the perfume dissipated, it was clear that there was no improvement in the situation.

Lets assume that the heater core and radiator are not leaking. You said there was no heat? Or, did you just turn the blower off because you could not stand the smell.

One of the problems could be a melting wire between the rheostat that controls the blower speed and the blower itself. Burning plastic is not nice! So, does the blower work at all speeds? Is there any noise while the blower is running?

Removing the glove box and the passenger kick panel, in that order, will allow access to the blower and rheostat. The wires are quite visible even with the knee brace still in position. All you need is a T25 driver and a very small screwdriver to release the plastic hinges from the glove box door.
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Keeping it running is better than buying new

It might not be a leak, some of the new cores have a coating that may 'burn off' the first few times that the vents are open. Remember, coolant always flows through the heater core even if you do not demand heat. I would wait a few weeks before bringing it back to the shop.

It wouldn't be difficult to remove the kick panel under the dash and then the side panel next to the gas pedal, allowing you to check for a leak.

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Keeping it running is better than buying new

Thanks, Klaus. I have taken advantage of your advice and wisdom in the past.

The "coating" issue does not seem to pertain in this case.

The smell began with my FIRST replacement heater core AFTER I used it for a full year.

The SAME smell (and it is very strong--and NOT sweet like coolant) is still there a week after the SECOND replacement core was installed.

Yes, that's right. The smell is exactly the same with the first and second cores. Which, of course, causes me to question whether there really was any leak in the first replacement core after a year of service.

I may be no expert, but it seems that the radiator mechanic's diagnosis of a leak in the first replacement core was wrong, now that the second replacement has been installed and I still have the same harsh acrid smell.

A 'radiator' shop doesn't normally work on heater cores, so what do they know. I suggest getting a T25 screwdriver, remove the kickplate on the driver's side and take a look yourself.

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Keeping it running is better than buying new