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      02-01-2020, 08:06 PM   #1
yakudi
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Exhaust smell in cabin from AC while stopped

Trying to figure this one out:

2011 X3 35i - wife's daily driver with about 79k on the odometer, she complained that she could smell the exhaust in the cabin.

Test drive proved her right - no smell when cold but in about 5 minutes of warm-up the AC pulls in the exhaust smell. While the vehicle is in motion no smell comes through, only when stopped. No smell with circulation on. I could also smell it with the hood open. Checked the head cover and gasket - no leak. Also didn't smell like oil burning.

Took it to an indy shop nearby. They said they couldn't smell anything but when on lift found the oil pan leaking slightly and very small leak in the crankshaft gasket. They claimed that this must be it but I was very skeptical. I checked things out from below and the leaks weren't bad. Told them not to do anything...

Then they claimed that a clamp needed replacing - the one that joins the exhaust to the Cat. $300 charged and the smell is still there.

What really confuses me is that the air intake for the AC is separated from the engine area by gaskets - so where is it pulling the fumes from?

Also, could any other gaskets be gone? Like the one between the cat and the exhaust manifold? Any ideas?

We're in the Boston area and would really welcome suggestions for good shop recommendations.
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      02-01-2020, 08:35 PM   #2
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You may know this, but there are 2 recirculate modes, manual and automatic.
Which mode are are using, "A" or the second unmarked one?

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      02-01-2020, 10:28 PM   #3
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Not sure it has anything to do with what mode you are using to bring air in the cabin. You mention AC but its winter in Mass, so do you mean heater? However, I don't believe it matters. You must have an exhaust leak since if your exhaust system was ok, it would only come out the end of the tailpipe.

Whether you have the heater on, AC on or just bringing in fresh air, it all comes into the cabin from the same place, via the cabin air filter which is located under the plastic cover on the passenger side just ahead of the firewall, like under the wiper area. Somehow, an exhaust leak is being sucked in there when the car is at standstill.

A proper garage should have an exhaust sniffer and can poke that around in the engine compartment and try to find the source. I would really have it inspected and wouldn't want anyone driving it till you get it fixed.
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      02-02-2020, 09:40 AM   #4
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Thanks so much for the replies, both.

Quote:
...there are 2 recirculate modes, manual and automatic.
Which mode are are using, "A" or the second unmarked one?
The smell goes away with the manual mode, still there with automatic - which tells me that the car is pulling in fresh air intermittently on A mode.

Quote:
...it all comes into the cabin from the same place, via the cabin air filter which is located under the plastic cover on the passenger side just ahead of the firewall, like under the wiper area. Somehow, an exhaust leak is being sucked in there when the car is at standstill.
You're absolutely right. It's cold here in Mass and we're running the heater. Fresh air is being drawn in through the cabin air filter (which I just changed as I was trying to diagnose).
My surprise is that the cabin air filter box seems to be separated from the engine compartment by gaskets. And there doesn't seem to be any outlet/inlet in that box (that I can see) which could pull in the exhaust gas other than the opening on top. I'm talking about the Box that the filter mounts in, not the snap-fit+plastic cover. Unless there is a weep hole in that plastic box that I'm missing. Very strange. By my logic we shouldn't be getting a smell at all. Anywho...

Is there an area on this forum where we recommend good shops/garages where I can get some recommendations for Massachusetts?
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      02-02-2020, 10:44 AM   #5
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Quote:
Originally Posted by yakudi View Post
Thanks so much for the replies, both.


The smell goes away with the manual mode, still there with automatic - which tells me that the car is pulling in fresh air intermittently on A mode.


You're absolutely right. It's cold here in Mass and we're running the heater. Fresh air is being drawn in through the cabin air filter (which I just changed as I was trying to diagnose).
My surprise is that the cabin air filter box seems to be separated from the engine compartment by gaskets. And there doesn't seem to be any outlet/inlet in that box (that I can see) which could pull in the exhaust gas other than the opening on top. I'm talking about the Box that the filter mounts in, not the snap-fit+plastic cover. Unless there is a weep hole in that plastic box that I'm missing. Very strange. By my logic we shouldn't be getting a smell at all. Anywho...

Is there an area on this forum where we recommend good shops/garages where I can get some recommendations for Massachusetts?
My point was that in order for you to smell any exhaust, there has to first be an exhaust leak. My guess from reading your description is that its up front, maybe in the engine bay or at least in the front part of the exhaust system.

One other thought, might sound nuts but....it is winter and exhausts from other cars stays lower to the ground so if you're at a red light in traffic, its common to suck in exhaust fumes from the other cars. Could it be as simple as that and there's nothing wrong with your car? Running the recirc on Auto allows the car to detect pollutants and shut out the outside world. So maybe there is something wrong with its auto feature or the smell isn't enough to trigger it to close the outside entry.

Try this, take the car for a ride and let it warm up, then sit in your own driveway with it running, away from other cars and turn off recirc with the windows up, heater on and see if you detect it. If so, put the recirc in manual mode (on) and see if you smell it and then try the auto mode and see if you smell it.

I don't know if there is a certain forum section for recommendations but no harm is just making a separate post and asking for them.
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      02-02-2020, 11:04 AM   #6
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Since the smell goes away in manual recirculate mode, I'm going with a slight oil leak that is dripping on the exhaust system which is burning off and causing the smell. Most likely at the valve cover gasket (VCG) toward the back which is hard to see, check with a mirror. This is a very common leak. If there were an exhaust leak before the CATs you'd hear a ticking sound.

For shops, check here
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      02-02-2020, 01:21 PM   #7
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Its not other cars - we've ruled that out by doing exactly what you describe. Stopping after warm with engine running and no other cars nearby.

I tried looking at the back with a mirror - its really tight with lot of pipes in the way. I did hear a slight ticking along with what sounds like a low continuous hiss. I think the ticking that I heard was just the belt.

I'll take it to a shop and report back. Thanks for the link.
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      02-05-2020, 08:25 PM   #8
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I would say VCG as well. I just had this done last week. I delayed the repair for about 2 months because it was fairly minor and at a few occasions there were fumes coming out the vent and it was the VCG. Good luck.
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      02-09-2020, 11:45 AM   #9
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So! The soup thickens a bit...

The shop did a full inspection again and says that the VCG is intact. They're of the opinion that the front crankshaft gasket is leaking and that is causing it. Could that be it?
Could a little drip from that gasket be heated by the radiator (or something else hot in that area) be causing the fumes?

Its a $300 repair but since I already paid these guys $300 for the clamp on the exhaust, I don't know if I trust their analysis. There generally trustworthy and also listed through the list provided by pungo above.
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      02-10-2020, 06:19 PM   #10
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Quote:
Originally Posted by yakudi View Post
So! The soup thickens a bit...

The shop did a full inspection again and says that the VCG is intact. They're of the opinion that the front crankshaft gasket is leaking and that is causing it. Could that be it?
Could a little drip from that gasket be heated by the radiator (or something else hot in that area) be causing the fumes?

Its a $300 repair but since I already paid these guys $300 for the clamp on the exhaust, I don't know if I trust their analysis. There generally trustworthy and also listed through the list provided by pungo above.
Difficult to say cause I can't smell it. Oil burning is a diff smell than exhaust. Does it smell like oil burning or exhaust? There really isn't anything up front that would be hot enough to smoke/burn dripping oil but as the car moves through the air, leaking oil pushes back towards the rear of the engine/car where there are things that will cause it to burn. If its oil, you should be able to see the leak and where its burning.

Just drive home, let the car sit overnight and then next day, get under it with a flashlight and white paper towel and start inspecting for it, if you see it, clean it up with the paper towel and some degreaser, clean it really well. Then take the car out and let the engine get up to normal operating temp, say 10 miles +. Then drive it home and do it all over again with the flashlight and paper towel. If its leaking, you will/should see it and since you know you cleaned it the day before, you will know that its a fresh leak. Try to see where the oil is going that might be burning it. However, to my nose, burning oil and exhaust fumes smell very different.
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