Coolant smell in cabin only when calling for heat.

The fist item on the checklist is the heater core. That is the first thing to question.

4C has a belly pan, making leaks a bit harder to discover -- especially tiny ones that come with a smell and might evaporate in minutes (such as pinhole heater core leak).

Are you checking the level in the expansion tank at the same (fluid) temperature and car on the same level ground every time?
A pinhole in the heater core will not necessarily remove a lot of coolant from the system, so you are checking for minuscule changes that hot coolant or a slight incline may disguise.

Also, if you don't usually use the windshield wipers, but did on those cold days, and still have the original washer fluid in the car, that has a very unusual smell too which permeates the cabin. Not likely the culprit, but worth mentioning.

FYI, another symptom of a heater core leak is that it will fog up your windows.

I usually get a whiff of coolant/antifreeze every time I turn on the heater. It goes away after a minute or so. I'm not concerned, always plenty of fluid in the reservoir.

Check the smell of your window fluid. Did you refill that recently? You my not believe it, but they smell almost the same in the 4C.

Depending on how infrequently you use the heat, you could have one of those leaks that seals up all by itself after some usage... It is really important to run the AC in the winter every so often and the heat in the summer every so often just to keep things going.

tibby said:

Check the smell of your window fluid. Did you refill that recently? You my not believe it, but they smell almost the same in the 4C.

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HEATER CORE

CLAMPS

All these links are situated @ the front of the car.....
Good luck...

Does it smell like something burning (like rubber or plastic burning)? And does it happen only after the first cold start (i.e. it doesn't happen if you restart the car once the car is warmed up)? And does the smell evaporate quickly and not return (until you start cold again)?

peppydee said:

I recently drove my 4C on a cold day and called for heat once engine temp was in normal range. First time I ever called for heat while driving it. The smell of coolant in the cabin was immediate. I headed for home and began looking for a cause or at least evidence of a coolant leak inside and outside the car. Found nothing. Checked the coolant level in the expansion tank, it was normal. Drove it for several more cold temp days always getting the coolant smell when calling for heat. Anyone experience this? Thanks!

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It’s been awhile since first posting about this problem but finally followed up on it by taking it to Benson Alfa and having them troubleshoot. Besides the smell, my windows were fogging up so I suspected a heater core leak. That’s what it turned out to be. Thank goodness for my extended warranty which is covering the replacement of the heater core.

peppydee said:

It’s been awhile since first posting about this problem but finally followed up on it by taking it to Benson Alfa and having them troubleshoot. Besides the smell, my windows were fogging up so I suspected a heater core leak. That’s what it turned out to be. Thank goodness for my extended warranty which is covering the replacement of the heater core.

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Thanks for the follow-up. A useful diagnosis for anyone with similar symptoms. 👏 👍