Gear Oil Smell in Cabin

[ATXGX470]

Gents,

I'm a new owner of a 2008 GX470. It's a very clean truck for the most part with an extensive service history. Currently it has 120K on the odometer.

As part of my ownership process I typically change all fluids. This always serves as a great way to get to know the vehicle and serve as a starting point to record my own maintenance intervals.

I decided to drain the front and rear diffs along with the transfer case. Filled them all up with Redline 75W90 gear oil.

The transfer case and rear diff were clean. The front diff was a little dirty.

What I'm noticing now is that when the HVAC is running on Auto setting and it's pulling fresh air from outside I get a faint gear oil smell in the cabin after stopping the vehicle. The smell last for a few seconds and then seems to dissipate. It can also happen intermittently. The one consistent time I will get the smell is if I exit the highway and stop at a stop light. My workaround has been to press the recirculate button as I approach the stop. Then there is no smell.

I don't think that I overfilled the diffs or transfer case.

Anyone have a clue as to what could be causing this? It was not happening before the gear oil drain/fill, so I'm scratching my head a bit.

Thanks for any info - !

 

[Stonefoot72]

Gents,

I'm a new owner of a 2008 GX470. It's a very clean truck for the most part with an extensive service history. Currently it has 120K on the odometer.

As part of my ownership process I typically change all fluids. This always serves as a great way to get to know the vehicle and serve as a starting point to record my own maintenance intervals.

I decided to drain the front and rear diffs along with the transfer case. Filled them all up with Redline 75W90 gear oil.

The transfer case and rear diff were clean. The front diff was a little dirty.

What I'm noticing now is that when the HVAC is running on Auto setting and it's pulling fresh air from outside I get a faint gear oil smell in the cabin after stopping the vehicle. The smell last for a few seconds and then seems to dissipate. It can also happen intermittently. The one consistent time I will get the smell is if I exit the highway and stop at a stop light. My workaround has been to press the recirculate button as I approach the stop. Then there is no smell.

I don't think that I overfilled the diffs or transfer case.

Anyone have a clue as to what could be causing this? It was not happening before the gear oil drain/fill, so I'm scratching my head a bit.

Thanks for any info - !

Did you change engine oil? I always tell myself I don't need to dig up the funnel, and every time I'm wrong and spill some engine oil on the block/manifolds... Smoking engine oil smells similar to 80/90 to me...if so, it'll prolly burn off in a day or 2

 

[jiggletits]

Gear oil smells like onions to me. Not even close to burning motor oil.

 

[ATXGX470]

@Stonefoot72 - Yes, I changed the oil too, but a week after I changed the fluid in the diffs and transfer case. Didn't spill a drop and was surprised at how well the metal piece below the filter housing actually diverted the oil from the spin on filter into my drain pan.

@jiggletits - Yes, I agree. Gear has a very distinct smell. It's unmistakable.

I wonder where the front diff or transfer case breather tubes route - and if they end up near where the HVAC pulls fresh air into the cabin?

 

[Stonefoot72]

Gear oil smells like onions to me. Not even

@Stonefoot72 - Yes, I changed the oil too, but a week after I changed the fluid in the diffs and transfer case. Didn't spill a drop and was surprised at how well the metal piece below the filter housing actually diverted the oil from the spin on filter into my drain pan.

@jiggletits - Yes, I agree. Gear has a very distinct smell. It's unmistakable.

I wonder where the front diff or transfer case breather tubes route - and if they end up near where the HVAC pulls fresh air into the cabin?

I figure if it was breather related, you would have smelled gear oil before you changed it. If you only noticed it after messing with fluids, it is probably excess spillage of some sort heating up on a surface like the block or exhaust...my best guess.

 

[ATXGX470]

I figure if it was breather related, you would have smelled gear oil before you changed it. If you only noticed it after messing with fluids, it is probably excess spillage of some sort heating up on a surface like the block or exhaust...my best guess.

Think you're probably right.

I need to take off the skid plates and clean the front diff and transfer case.

I'll report back if it makes a difference.

Appreciate the input!

 

[Tywrap]

I just had the same thing happen to me. Changed all the fluids and my first trip out today ,about 15 min in, I could smell gear oil in the cab with hvac on. Was odd.

 

[OllieChristopher]

This might be a stab in the dark but do you have an in-cab mounted air compressor with lines going to air lockers? If so and your diff vents are plugged then that is your issue.

 

[ATXGX470]

This might be a stab in the dark but do you have an in-cab mounted air compressor with lines going to air lockers? If so and your diff vents are plugged then that is your issue.

@Tyrap - After posting this, I decided to try not turning the HVAC recirc on/off as I approached stop lights and stop signs on the way home from work tonight. I get the occasional mild waft of gear oil, but I think it’s getting less.

I had fluid flow out of the fill plugs on both diffs and transfer case when I changed fluids and I made a good effort of cleaning the areas around the fill plugs with simple green and a rag. Wonder if I missed areas below the plugs, and as things heat up, the residual left over gear oil is slowly burning off and getting sucked in through th cabin when I slow down and stop.

Time will tell - bit I still plan to do a better job of cleaning up soon of this problem persists. The smell of the gear oil is very strong. I can pick up the scent each time I open up my toolbox drawer that contains my gear oil pump - and it’s been cleaned and put back in a box.

@OllieChristoher - That sounds like a great setup! I’m just getting started with this rig, so I’m not in that deep yet...but I’m definitely on the edge of a slippery slope.

Again - appreciate all of the replies.

 

[Tywrap]

No in cab compressor here either. I'm in ATX's camp and just started with my GX as well.
While I had the GX on the lift for over a week , tearing out all the stock suspension and control arms I drained all 3 (diffs and tcase). Cleaned it all up with brake clean and torqued everything back up looking for leaks. Only thing I can think off is I did replace the rear diff breather and routed it up towards where the airpump used to reside. Might be a negative pressure thing pulling outside air through a vent. Now that the rear vent isn't rusted shut

 

[OllieChristopher]

@OllieChristoher - That sounds like a great setup! I’m just getting started with this rig, so I’m not in that deep yet...but I’m definitely on the edge of a slippery slope.

I actually like the bagged up air compressors that I can move from rig to rig. I'm all about simple. Some of these GX builds blow my mind on how complicated and serious fabrication is involved.

My wife and I are seriously considering a GX460. My plan would be simple and functional as a daily driver for camping without all the "overloading fluff".

 

[jiggletits]

It is mostly fluff. Lots of fluffers into ‘overlanding’.

 

[GXO]

I get this. It is venting from the diff. The front stinks! I have ARB air lockers so I get even more of a smell once it is warm. The front diff vents on the driver side frame near the fuse box (down lower). I have found if you fill more than spec on the front diff it will sling gear oil to the breather and smell. If you remove the fill plug and let it drain down to where it is not over flowing it will stop. I have had a bad oring in my ARB happen and it has caused this smell (and a fine gear oil spray when I lock/unlock my lockers) but that is a different problem.

Edit: Since I mention over capacity, I figure I might as well put the capacities! The front diff is very particular, and even less oil is needed with an ARB or other locker as the carrier is so much larger and takes up more of the potential volume:

Front Differential
Oil capacity 1.48 qt. (1.40 L, 1.23 Imp.qt.)
Oil type and viscosity* Toyota Genuine Differential Gear Oil LT 75W-85 GL5 or equivalent

Rear Differential
Oil capacity 2.85 qt. (2.70 L, 2.38 Imp.qt.)
Oil type and viscosity* Toyota Genuine Differential Gear Oil LT 75W-85 GL5 or equivalent

Transfer Case
Oil capacity 1.5 qt. (1.4 L, 1.2 Imp.qt.)
Oil type*Toyota Genuine Transfer Gear oil LF or equivalent
Recommended oil viscosity SAE 75W

 

[ATXGX470]

I get this. It is venting from the diff. The front stinks! I have ARB air lockers so I get even more of a smell once it is warm. The front diff vents on the driver side frame near the fuse box (down lower). I have found if you fill more than spec on the front diff it will sling gear oil to the breather and smell. If you remove the fill plug and let it drain down to where it is not over flowing it will stop. I have had a bad oring in my ARB happen and it has caused this smell (and a fine gear oil spray when I lock/unlock my lockers) but that is a different problem.

Edit: Since I mention over capacity, I figure I might as well put the capacities! The front diff is very particular, and even less oil is needed with an ARB or other locker as the carrier is so much larger and takes up more of the potential volume:

Front Differential
Oil capacity 1.48 qt. (1.40 L, 1.23 Imp.qt.)
Oil type and viscosity* Toyota Genuine Differential Gear Oil LT 75W-85 GL5 or equivalent

Rear Differential
Oil capacity 2.85 qt. (2.70 L, 2.38 Imp.qt.)
Oil type and viscosity* Toyota Genuine Differential Gear Oil LT 75W-85 GL5 or equivalent

Transfer Case
Oil capacity 1.5 qt. (1.4 L, 1.2 Imp.qt.)
Oil type*Toyota Genuine Transfer Gear oil LF or equivalent
Recommended oil viscosity SAE 75W

Thanks for posting this and for confirming that the front diff is very particular with respect to fill capacity.

I drained/filled the front diff last and I did pump in too much fluid by mistake. I let it drain out of the fill - but not all the way. I actually went back after I had the smell initially - and removed the fill plug and let it drain more...but not until the fluid completely stopped coming out. I'll try again and will let it stop to see if that resolves the issue.

Appreciate your help!

 

[ATXGX470]

Thanks for posting this and for confirming that the front diff is very particular with respect to fill capacity.

I drained/filled the front diff last and I did pump in too much fluid by mistake. I let it drain out of the fill - but not all the way. I actually went back after I had the smell initially - and removed the fill plug and let it drain more...but not until the fluid completely stopped coming out. I'll try again and will let it stop to see if that resolves the issue.

Appreciate your help!

OK - Quick update...

Just got back from another out of state road trip in the GX.

Before leaving, I drained the front diff again and found that I had about 1.5 quarts.

I filled the front diff up again and put in just a little less than 1.5 quarts to see if it made a difference.

At first it did - while driving around town at low speeds. However, once I hit the highway and drove at 75-80 the smell in the cabin came back again once I stop with the HVAC on. Not quite as strong, but it’s still there.

I used Redline 75W90 gear oil. Wonder if I should try Toyota 75W85 as mentioned above with the fill capacities...?

I will continue to troubleshoot.

 

[GXO]

I cleared my front and rear diffs as causes, but I do need to clear the transfer case. That vent is VERY close to the cab and the vent being plugged or off the tcase would cause fumes when warm and not moving. I will be crawling under there!

 

[Rednexus]

The breather plugs are cheap and easy to replace:
Amazon product ASIN B06XHBY38X

 

[ATXGX470]

The breather plugs are cheap and easy to replace:
Amazon product ASIN B06XHBY38X

Interesting...

@GXO - Are you saying that you cleaned out your breather tubes? If so - how? I took a look at the front diff breather tubes while under the truck last time, but it was very tight and I could not see much beyond it coming out of the diff.

@Rednexus - Does that product replace the breather tube that comes out of the diff? i.e. Do you disconnect the stock breather and replace with that Dorman product?

Thanks for your help!

 

[GXO]

No, I just made sure the diffs were not over full and the smell wasn't coming from the diff. I had some issues up front (over full). Going to do the rear and tcase when I get some time.

 

[Rednexus]

The stock differential breather should have a rubber hose leading from the differential to the cowl area under the hood. The hose is then terminated with the breather plug, which acts as a check valve to prevent water/debris from entering the hose leading to the differential. You should be able to remove the stock breather plug from the underhood hose and replace it with a new Doorman (or OEM Toyota) plug.