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Discussion Starter #1
I have a strong odor in the cabin when I start up my X5 (4.4L V8) when it’s cold. Within about 2 minutes it goes away. The car only has 40,000 miles and looks clean in the engine compartment (no visible oil or antifreeze leaks). I’m thinking it’s related to the catalytic converter since it only happens when the engine is cold.

It’s hard to replicate since it goes away in a few minutes. Any ideas?
 

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Nuclear engineer
02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
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Position / condition of your AUC button / flap / detector? AUC = Automatic Recirculated Air Control.
 

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///Monkeyazz Duck
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Other candidates:

Roadkill on the exhaust system.

Condensation in your climate system, due to turning off the A/C compressor in the winter. (The BMW system is designed to have the A/C compressor running 365 days per year). Trying to outwit the system commonly results in a "musty gym sock" odor.

Clogged catalytic converter. Unusual with your mileage, but one tank of bad fuel can do a lot of damage.
 

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Discussion Starter #4
Position / condition of your AUC button / flap / detector? AUC = Automatic Recirculated Air Control.
It’s normally open allowing outside air, but when I set it to manually recirculate cabin air only, which prevents outside air, it doesn’t smell as bad.
 

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Happily Driving
2018 X5
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What kind of odor is it? Once I had a car that had an antifreeze leak that would pool om the cool engine block overnight. Once the car warmed up, the antifreeze would burn off and I would get what I thought was an exhaust smell in the cabin, which would go away when I forced air re-circulation. Only after the leak got bad enough that I noticed drips on the ground were we finally able to diagnose the problem. Once the leak was fixed, the smell went completely away.
 

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Discussion Starter #6
It***8217;s hard to describe the smell. To me it smells like rotting grass from underneath the lawn tractor. I***8217;ve checked under the hood, and there***8217;s no visible oil or anti freeze. It***8217;s very difficult to replicate since it only smells right when the car starts and only when it***8217;s cold.
 

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It's hard to describe the smell. To me it smells like rotting grass from underneath the lawn tractor. I've checked under the hood, and there's no visible oil or anti freeze. It's very difficult to replicate since it only smells right when the car starts and only when it's cold.
@autoworld......."To me it smells like rotting grass"; Bet this is from A/C Evaporator chamber. When is the last time you replaced your cabin filters?

Good luck & hope this helps

Here's an A/C cleaning TIS link

https://www.newtis.info/tisv2/a/en/e70-x5-xdrive35i-sav/repair-manuals/64-heating-air-conditioning/64-51-heating-air-conditioning-unit-evaporator-shift-elements/2crcTsC

Here's a link to one product with a good video.

https://www.amazon.com/Lubegard-96030-Evaporator-Heater-Cleaner/dp/B0007PHD0S/ref=sr_1_5?ie=UTF8&qid=1545675516&sr=8-5&keywords=a%2Fc+cleaner+car

Here's another video, this is foe E39 but similar for your X5

https://www.youtube.com/watch?v=duey0y-GrfU
 

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Discussion Starter #8
Thanks to all who responded. I’m still trouble shooting, but I may try to clean the HVAC system as suggested.
 

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Nuclear engineer
02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
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Within about 2 minutes it goes away. ... It’s hard to replicate since it goes away in a few minutes. Any ideas?
Then not a smelly evaporator
 
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