Burnt smell in cabin at high speed in cold weather

[grilled cheeseus]

This is a weird one. 2007 Yaris liftback 5MT 3 door, 102k miles.

The burnt smell is not distinctly burning oil or burning plastic. It could be burning rubber but I'm not sure. The smell is accompanied by a scratchy throat and watery eyes, not good.

I ONLY notice this when all of the following are true:

• Cold weather (around/below freezing)
• Vent setting on fresh air (It mostly goes away on recirc, but I can't drive for hours that way.)
• At highway speeds, maybe 55+ MPH. If I speed up the smell gets worse.
• After 30-45 minutes of driving

The car is well-maintained with no other issues. Last spring, a shop replaced my drive shaft seals at the transmission, said there was some seeping of gear oil. Didn't notice the issue all summer and now it is back. Just looked at the drive shaft seals and they're still good.

My questions for the hive mind:

• Where exactly does the cabin vent system take in fresh air? I'm wondering if something near that intake is producing the smell.
• Can the heater core itself produce this smell? (Does my Yaris only heat using engine coolant or is there also a resistive heating element?)
• Has anyone else experienced or diagnosed this problem before?

Thank you! I'm driving across the USA next month and would like to breathe easy.

[tmontague]

Have you checked your exhaust header to make sure it was clear of anything?

If that checks out then remove the glove box and check the cabin filter behind it. Use a light and see if anything is stuck in there or if there is any residue.

Is the smell there if you are traveling at highway speeds without the fan on? If not then it could be an issue with the motor potentially.

I haven't heard of this issue before, i'm interested to see what others think.

[JBinc]

I have a similar symptoms with my '07 Yaris 4dr w/205K miles. I was driving on the highway and suddenly my exhaust was twice as loud as normal. I put it on a hoist yesterday and found that the connection point where the pipe from the exhaust headers meets the section of pipe just before the cat was loose. There was no spring between the two flanges, just two bolts. I'm thinking the gasket deteriorated, causing the gap resulting in the exhaust noise.

This connection point in the exhaust lies just to the right of the driver's foot on the underside of the car. It's possible the exhaust gases from the leak are heating things it wouldn't normally come into contact with. Maybe your heat shield is also gone (due to rust/deterioration). Check this point in your exhaust if you're able to get under it.

[WeeYari]

An '07 definitely needs to have the condition of the gasket between exhaust header and downpipe checked out.

[jcboy]

i have this in my '12 manual. if you search burnt/burning rubber during hard acceleration/high speed driving you'll find a few matches.

seems to be a sticky clutch, just a hunch.

[grilled cheeseus]

Originally Posted by tmontague

Have you checked your exhaust header to make sure it was clear of anything?

I cannot see the entire header, but no other parts are touching the sections that I can see. Plenty of clearance.

Originally Posted by tmontague

If that checks out then remove the glove box and check the cabin filter behind it. Use a light and see if anything is stuck in there or if there is any residue.

Did this. The filter is just old-looking, no other issues in sight, blower spins freely. I'll replace the cabin filter but I suspect the problem lies elsewhere.

Originally Posted by tmontague

Is the smell there if you are traveling at highway speeds without the fan on? If not then it could be an issue with the motor potentially.

Good question, but I doubt it's the blower motor because the smell only happens when pulling in fresh air, not on the recirc setting.

Originally Posted by JBinc

This connection point in the exhaust lies just to the right of the driver's foot on the underside of the car. It's possible the exhaust gases from the leak are heating things it wouldn't normally come into contact with.

Interesting theory, JBinc. I'll look at that gasket and the heat shield more closely in the light of day.

Originally Posted by WeeYari

An '07 definitely needs to have the condition of the gasket between exhaust header and downpipe checked out.

You're the second person to mention this; will do.

Answering my own question from earlier: I think that fresh air for the cabin is drawn from the black plastic grille between the windshield and hood toward the passenger side, outside the engine compartment. It feels unlikely that an exhaust leak under the hood would result in gases getting ingested by that grille, but who knows which ways the air flows at high speed. JBinc's theory about leaked exhaust gases heating up parts that shouldn't be heated is really interesting.

Originally Posted by jcboy

i have this in my '12 manual. if you search burnt/burning rubber during hard acceleration/high speed driving you'll find a few matches.

seems to be a sticky clutch, just a hunch.

Hm - I have no other clutch issues; no slipping, sticking, or weird engagement. Also, no smell during hard acceleration.

Thanks everyone. I'll take another look tomorrow and report back.

[daroccot]

Yeah I know this is an old post, but the answer wasn't communicated and I have the same smell. Same conditions as the OP. Gasket b/t header and exhaust is new. Only smell at wot usually going up steep hill on highway.

[grilled cheeseus]

OP here. The problem went away on its own and was never conclusively diagnosed. I live in the desert Southwest (USA) now. One possible explanation: heated winter air is very dry, rough on the throat/sinuses, and the 'burnt' smell was partially/wholly imagined -- a wet towel in the car (and/or using recirc) seemed to help with this in cold weather. With attention paid to humidity, I didn't notice any issues for the entire 4,000 mile trip here.

I've gotten checked out by an exhaust shop, they couldn't find any leaks despite 11 years and 120k miles on the original exhaust system, although you can still cover the tailpipe with your hand and the car keeps running (maybe some gasket gives way at elevated exhaust pressure).

daroccot, "only at WOT" suggests a different etiology for your problem, as mine seemed to also happen at low-throttle cruise. If you're sure your exhaust doesn't leak at WOT, I'd look for an intermittent fluid leak that maybe only happens at WOT (when all the engine-pumped fluids are at higher pressures).

Or, maybe some fluid (or just tar/gunk from the road) is landing on your exhaust, but the pipes only get hot enough to burn it off at WOT.

[dogsridewith]

Monday, on the way to triple recall, I had a hot smell 15 miles into cool morning commute after washing car the night before. Mind thought maybe the water got some of fall-sprayed "Corrosion Block" (mostly at all the car's visible fasteners and seams I could hit) onto something hot. Also that I may have passed someone's burn barrel/pit.) And that I've never really checked new looking 137k exhaust system.
(I've also had a couple passing instances of the swamp-foot thing odor these cars said to get...though I don't feel what I've read on the forum so far says exactly what is doing this...and might have just passed a swamp or cemetery or something.)

[08yarisdriver]

I get this as well in cold weather mines more of a melted plastic odor and only seems to cause the odor when the control is on fresh air and so far either vent or defrost and gets more pronounced when you hit the accelerator and get the rpms up a bit not sure what is causing this odor

08 yaris HB/LB
manual transmission

[DarkShadowFox]

hey me too it smelled like burnt oil or trans fluid in my '15 im convinced that these cars are not designed to be heavy duty runabouts

[grilled cheeseus]

08yarisdriver and DarkShadowFox, like others here have said, I suggest replacing the exhaust donut between manifold and cat if you haven't yet.

http://www.yarisworld.com/forums/showthread.php?t=59145

This gasket is known to degrade and leak un-catalyzed exhaust into the cabin. My car got quite a bit quieter after this fairly easy job.

Originally Posted by DarkShadowFox

im convinced that these cars are not designed to be heavy duty runabouts

Really? A couple months ago I drove my '07 hatchback (which has seen 10 salt belt winters) from New York to Arizona, pulling about 1,000 pounds of loaded camping trailer, including over mountain passes. This was its third cross-continent trip, and it made all three trips with zero issues. So, I think these are fairly heavy-duty as far as cars go. :)

[08yarisdriver]

im looking toward my alternator actually. I poked around under the hood when the odor came through the vents. my engine gets a high load out of nowhere a lot of times it seems. makes the alt belt squeak some then goes away this is intermittent. if I unplug the 4wire plug on the alt it goes away soon as you plug it in it squeaks again. anybody know what the 4wires input/output to ? smell seemed strong around the alternator/ pass side of engine no smell on driver side but ordinary engine odors oil etc

[dogsridewith]

I got it WOT on uphill pull last week. Might just be overheated components of the "dust" that settles on everything underneath, including manifold, pipes, cat converter...where there's some organic content in that dust. (some horse droppings in my neighborhood.)