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I'm new here as a poster. Have done a lot of searching though, but this issue I'm having seems to be a rare one.
I've got a 2005 S-Type V8 NA. It's equipped with a windshield defroster that even now still mostly works. There are bands where it doesn't and bands where it does, but it's effective for about 70% of the windshield, which is very useful on the frostier days.
The issue I'm having, and believe me, it took a while to narrow it down because the windshield heater is automatically enabled at cold enough weather, is that when the windshield heater is on, after a minute or so, a sweet-ish sort of burning smell permeates the cabin. It's not strong enough to be cough-inducing, but it's very noticeable and definitely concerning. The smell has some resemblance to that of 3D-printing PLA, but it's not quite the same. If it's not a vaporizing liquid, then it could be some kind of melty plastic smell.
I first noticed the fumes last autumn when the weather got cold enough, and it took me months to figure out that it's not an exhaust leak or a coolant leak or A/C leak or moisture in the vents or anything like that. It only occurs when the windshield heater is activated.
I just came back from washing the inside of the windshield on the suspicion that there's just some old sneeze residue or some other gross gunk coating the inside of the windshield, that off-gasses when it warms. Alas, cleaning the windshield didn't help: A test drive with the defroster afterwards produced the same smell.
I suppose the next thing to do is to look at the service manuals to find whatever module controls the defroster and to go look for toasty wires between that and the windshield. Before I go tearing the car apart though, I wanted to ask you knowledgeable cat-wranglers if this sounds in any way familiar. Would be neat if somebody had already done the work to fix this kind of an issue.
Thanks for taking the time to read this post! Let me know if you can think of anything!
Fair enough. That's a reasonable suspicion and seems sensible. However, while I'm not familiar with the smell of the coolant, my mechanic did catch a whiff of the smell and didn't think it smelled like coolant. Furthermore, I'm puzzled as to the mechanism, by which the fully electric windshield heater would be connected to a heater core leak. The only thing I could think if is coolant mist being sprayed onto the windshield from the air vents and then evaporating when the windshield is heated.
That's still implausible, because a) I washed the windshield inside thoroughly and b) there's no smell when the windscreen heater is off.
I wanted to update this thread as I finally got around to figuring this out a couple weeks ago when the weather started to get colder again.
I removed the right side A-pillar cover and discovered the connectors for the heated windscreen. The connectors were regular automotive spade connectors at heart, but the ones on the windshield side had these soft white plastic insulator shells. The one high up was fine, but the one low near the dash was a melted mess. Apparently the connector was making poor contact and had heated up enough to melt the plastic. This was the source of the sweet-ish plasticky smell I had been wondering about.
I clipped out the melty connector on the car side and scraped the soft melted plastic off the windscreen connector, cleaning it well. Then I stripped some of the wire on the car side wire, crimped a new connector there and put a bunch of heat shrink tubing around the wire. I used the old connector on the windscreen side, because it would've been difficult to change and didn't look corroded. Insulated it all with the heat shrink and called it a day. No more smell and the windshield still heats up.
Hopefully this will help someone somewhere before their car burns down!
Windshield defroster smell
