Smells like propane or natural gas

[Frosty]

Okay, recently the inside of my '08 GMC Envoy Denali has started smelling like propane or natural gas, after I start the car and run it. The defroster or  heater is on and the fan is switched on high when this occurs, This is not the rotten egg,/hydrogen sulfide smell that you would associate with the a bad catalytic converter of days of old either. At first I thought it was the burning grease of the bad left front hub I just replaced a few days ago. It was getting pretty noisy and I had it replaced at Tuffy, but the smell remains. 

Doing my research online, I have learned that propane and natural gas companies add the odorant called ethylmercaptan (or "mercaptan" for short) in order to allow people to smell small leaks since propane and natural gas do not have a natural odor or scent. This is the odor I am smelling.

It's been extremely cold here in Michigan, so I am waiting for it to get above freezing before I do too much checking. I think it is a very remote possibility of some dead critter getting into the vehicle's ventilation system, but I don't think rotting flesh would smell like this either. I suppose it could be problem with the exhaust system, but again, this is not the typical smell you associate with the bad cat.

One suggestion I have come across is that perhaps the battery is damaged or a plate has come loose internally and it has come in contact with another and it is emitting this odor. My battery is covered by battery box so I am not able to look at it for any external damage or remove it for a load test under the weather warms up a little. The car starts fine so I don't have any obvious sign of a bad battery at this stage. This is my first/likely suspect. The battery is only 1-2 years old. I also plan to drop the glove box and check under the dash for possible dead critters. After that, I am really out of ideas of what to check. Most of the online forums I have checked don't really answer this unique odor. So I am open to suggestions.

[havoc1482]

It could totally be a dead animal. Dead stuff has a distinct smell and its not a sulfur smell.

There have been times when I've mistaken a rotting mouse carcass that my cat dragged in to be a propane leak.

I remember one time walking into my kitchen thinking that the stove was on, but not ignited, only to find a dead mouse under the counter.

 

This is the time of year where all sorts of critters will find their ways into your car. I just had to clean a mouse nest out of the flywheel bellhousing of my tractor. I have no idea how the hell they manage to get into that area. Its amazing.

 

[Frosty]

You may well be right Havoc. My truck sits outside , so I don't picture it as the ideal nesting/refuge area for a critter. However, as cold as it gets here in the winter, I can see were getting the hell out of the cold, wind, and snow might be enough. Again, having been around enough dead critters before, this is the not the smell I am expecting. Still, you maybe right.

Its suppose to be above freezing tomorrow afternoon, so hopefully I can find some time to pop open the hood and the dash and look around.

Edited December 22, 2016 by Frosty

[havoc1482]

Does the smell come on if you were to run the blower's with the car off? Maybe try other settings? (Recirculation, external) Does it only come out of certain vents (Windshield, feet, ect) or all of them? That might help you isolate it from being something within the system as opposed to the system drawing the smell from an external source.

I just did a some searching and you may also want to check the transmission. Apparently in some cases, burning tranny fluid can have a "propane" smell.

Sent from my S60 using Tapatalk

[Ringo64]

Sounds like Havoc might be on to something. 

[Frosty]

I had not run across the burning tranny fluid explanation before. With 157K miles on it, anything is entirely possible.

To answer your question Havoc, I can smell it both inside and outside the car after I have started it, but not before, with the car totally cold. I smell it both with just the defroster on and with the heat too. I am not using the recirculation at this point.

[havoc1482]

The tranny thing I found I think someone was having the problem or similar on an Acadia.

If it's inside and outside I think we can safely rule out a dead animal or something inside the system. Have you popped the hood and looked for any obvious signs of gasous leaking/burning, especially around areas that could easily get into the dash/HVAC?

Sent from my S60 using Tapatalk

[Frosty]

I just finished my underhood inspection. I pulled the battery completely out, no external signs of damage and no odor from it. I took a flashlight to all the cracks and crevices I could shine it into, and found nothing. I don't consider this an exhaustive search but at least a thorough once over. I have not yet crawled under the car since the driveway is still quite wet from the melting snow.

I have done a preliminary examine of the interior by retracting the seats and folding down the rear seats and reaching under both front seats, Nothing as yet. I still need to pull the glove box screws to gain access behind the dash.

Nothing obvious as yet.

[Ringo64]

Why is it all weird problems are not easily found  

[notallthere]

Quit farting in your car before you get out at night.

 

[Frosty]

On 12/22/2016 at 6:37 PM, notallthere said:

Quit farting in your car before you get out at night.

 

How'd you know that? 

[notallthere]

We hang out just enough for me to know.

[Frosty]

Wise acre!

[Frosty]

On 12/22/2016 at 4:29 AM, havoc1482 said:

Does the smell come on if you were to run the blower's with the car off? Maybe try other settings? (Recirculation, external) Does it only come out of certain vents (Windshield, feet, ect) or all of them? That might help you isolate it from being something within the system as opposed to the system drawing the smell from an external source.

I just did a some searching and you may also want to check the transmission. Apparently in some cases, burning tranny fluid can have a "propane" smell.

Sent from my S60 using Tapatalk

 

On 12/22/2016 at 8:22 AM, Ringo64 said:

Sounds like Havoc might be on to something. 

He was indeed close.

On 12/22/2016 at 6:37 PM, notallthere said:

Quit farting in your car before you get out at night.

 

I think we've found the problem, it was not bad farting either. I will to give kudos to Havoc as he was close but it was not transmission fluid that was burning. I took the Envoy to Tuffy today. It took six guys at two different Tuffy shops to find the problem. It appears to be the front differential-to-axle seal, on the driver's side, that is leaking. When the axle spins, it is slinging the leaking diff fluid onto the bottom side of the driver's side exhaust manifold and it burns the fluid. I only smell the propane smell at idle or near stop conditions, and not at speed because the speed of the car blows the burning fluid away from the interior air pickup. The leak is not bad enough to leave puddles on the driveway either, so there was no clue that I had a leak at all until you got the car on the lift.

So now most of the front suspension has to come apart in order to pull the front diff out and replace the seals and add back the lost diff fluid. So that is a couple hours worth of work to put the diff on the bench and repair it.

Looking from the transmission back towards the front of the car, you can clearly see how wet the driver's side exhaust manifold is.

Looking at the driver's side differential / axle assembly, you can clear see it has been leaking.

Edited December 30, 2016 by Frosty

[Frosty]

Here is the ruined differential-to-axle seal. It doesn't look like much until you are holding or you are standing next to it.  Holy Mackerel does this thing stink ! That is why I am holding it on a box. So it does not get on my skin or clothes. It is saturated with burnt synthetic diff oil. It gave me an instant headache from smelling it. It was like the smell propane, burning tires, dead fish, and poo gas all at once. Take my word for it, it was seriously nasty bad!

The mechanic said he sprayed everything down with brake cleaner after he was done to get rid of the old diff oil. There is still a slight smell, he said that some of the old diff oil may still need to burn off but he said if the smell sticks around after a couple of days to bring the car back.

Edited December 30, 2016 by Frosty