Burning smell coming through vents into cab

10 DCSB, no problems prior to this. Drove to work one morning last week and we had negative temps, truck ran fine no problems on way to work. Walked out to truck after work and noticed what seems to be a diesel exhaust/burning smell very prominent in the cab of the truck and coming through the vents and it is very nauseating. The smell is also very prominent in the engine bay but only on the passenger side. All fluids seem to be fine and at normal levels, fan speeds work normally, I pulled the resistor and there is nothing wrong with it. I'm perplexed and completely lost on where this smell is coming from. Any suggestions on what to check or where to look?

 

Look for oil dripping on to exhaust

 

Might be heat shields going out. Other members posted very good probable causes as well that are worth checking out.

 

If not a leak my smell was the belt. Look at the belt and see if an idler or tensioner is worn out. Slipping or dragging belt smells.

 

^^^^^This^^^^^

I had the same thing happen in my Ram a few months ago. The smell is awful.

 

I've checked the engine bay pretty good, saw no leaks, went and power washed the engine with degreaser and smell still continues after cleaning engine.

Thanks I thought that might be the culprit as well, no leaks at all in the engine bay.

Heat shields? Please elaborate.

Thank you, I'll definitely check it out as it is the original belt and I notice there are quite a few cracks in it.

 

Does the smell get stronger of dissipate as you're driving?

Maybe look around your exhaust for anything that might have leaked, spilled, or dropped onto your exhaust after manifold. Cats can get very hot if anything dropped onto it, can burn causing off gassing.

Look for possible overheated/melted wires too.

 

Have you checked the cabin and intake air filter?

 

It gets a bit stronger as the truck is running and I'm driving, definitely coming in through the vents for sure. Weird thing is I can still smell it in the cab and engine bay when truck is parked and has been parked overnight.

I don't believe there are any leaks anywhere as I've thoroughly power washed the engine bay and checked for leaks and have found none. Also crawled under the truck to look for any burned wires up in underside of engine bay and have found nothing.

First thing I did, it's completely clear except the filter.

 

How about blower motor, or any of the vent flap motors on passenger side? Still thinking some electrical wiring overheating, since you've ruled out a fluid leak. The smell has to come from somewhere...

Try driving with vent fan running/not running...any difference? Pull vent filter and motor (easy job) look up ducts for blockage, at motor for worn stuff or smell near wires or motor shaft?
.

 

Another vote for the belt potentially rubbing on a seized pulley or something. Does the AC/ defroster work?

when I lost my AC, the belt was rubbing on the compressor pulley which produced a strong burning smell

 

I have driven with fan off and smell dissipates immensely but still there ever so slightly. It's just weird because I recently went on a 400+ mile round trip and had none of these problems, 2 days after we had negative temps for 2 days and that's when this started. I will pull cabin air filter again and possibly the motor and try to look up into the vents if at all possible. I live in a pretty small town, not much choices in way of mechanics...I even took it to the most knowledgable mechanic here and he was stumped as well, his advice was "go wash your engine".

All pulleys are working normally and spinning with the belt. AC defroster does work. Smell is much less noticeable when blowing cold air, almost unbearable smell blown into cab when switched to hot air.

I have crawled underneath the truck and looked at everything underneath, no plastic bags stuck anywhere and no wiring anywhere near exhaust components that could produce a burning plastic smell.

 

Pulled filter and motor, both are fine, resistor is good, nothing stuck up in vents as far as I can see. I am fucking stumped and royally irritated!

 

Heater core? How’s your coolant level?

 

You may have to crawl through your engine bay and see if you can narrow area by highest concentration of smell to get to the source.

...or get one of these???
http://www.fivesenses.com/equipment/nasalranger/nasalranger/

 

You just beat to this...

Also look at oil for coolant, and coolant for oily residue. Might be small crack in block or head causing old and coolant to cross contaminate, which can lead to odd smells.

 

Dead animal in the heating ducts? Smell pretty bad until they mummify.

 

They already told you your issue? It is a valve cover gasket leak. I just did this last month.

 

Dead animal. Temps got low animal got in thru cowl and died

 

A/C compressor clutch probably going out.