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Craig B
03-12-2007, 18:56
There is probably an answer to this somewhere on the site, but I can't find it. There is a vent? line that comes out by the drivers side front wheel. A thin black hose with a cap/breather on the end. I have had the truck for 3 1/2 years without a problem but the last week or two this vent has been leaking oil, not much, just enough to mess up the garage floor. I traced it back two or three times but lose it every time. I am wondering what the vent is for, where it goes, and what could be causing it to drip all of a sudden?

Any help would be appreciated.

Craig

'03 Sierra 3500 125,000 KM, just stock
taznj63
03-13-2007, 08:56
Is your truck 4 wheel drive?
It could be the breather hose for the front diff.
Also the trans breather is supposed to be up by the firewall, could this have come loose and fallen down?
What color is the oil?
Craig B
03-13-2007, 18:45
Sorry, yes 4 wheel drive, I suspect it is the front dif breather but don't know for sure. As I said I have traced it back but keep losing it. The oil is light and clear, not engine oil, as far as colour, well my colour blindness makes that difficult.

Craig
mattb5150
04-28-2009, 10:25
Hey Guys,

Just noticed some fluid drips on my garage floor. Looked in wheel well and there is oil splattered around, looks like its been coming from the vent cap for front diff. I only use 4wd about once a month and I had it in 4 wheel last week, checked and its in 2wd now according to the indicator light. I have the updated white plastic plug in the diff. Any ideas? 2003 Sierra 107k miles. Mobil 1 75w-90 fluid changed at about 80 k miles.

Matt
mattb5150
04-29-2009, 08:13
Wondering if I should drive it in this condition? Better check level tonight. Anyone.

Matt
jbplock
04-29-2009, 16:17
Matt,

I would check to see if the white cover is loose .. might be good to remove it and check the o-ring that seals it .. also check the vent hose ... if the leak is diff lube it will have a strong sulfur smell ...
mattb5150
04-29-2009, 20:31
It's definitely coming out of the vent tube cap. Found a GM #PIP3454D from July 13, 2007 for a front axle fluid leak, says to install a filter in the vent tube to prevent oil form coming out of the tube. Anyone heard of this or have the filter part number?

Matt
mattb5150
05-01-2009, 13:19
Well I jacked the truck up removed the wheel and checked the tightness of the white cover, I wouldn't say that is was loose, but I was able to turn it another 1/3 of a turn. I removed the cover checked the o-ring and the vent and all seemed fine. Before I re-installed I applied some RTV to the threads as has been suggested in other posts to keep from loosening again. I just don't see how this could have occurred especially after seeing the design of the white cap with the metal vent that hangs down and such. The small black cap at the other end of the vent hose had quite a bit of dirt and tiny rocks in it. Cleaned that out with some carb cleaner and re-installed also.

Matt
DmaxMaverick
05-01-2009, 15:48
You may also want to check the routing of the vent hose. If it has any dips kinks in it, lube will accumulate in the "trap", and blow out as the diff warms up. The hose must be clear, and continuously descending from the vent to the diff. If the diff was overfilled (possible if not done on a level surface), it could cause it to leak lube out the vent, as well.
mattb5150
05-01-2009, 20:32
The tube ascends from the white cap up to fender liner then turns down so the trap is upside down with the hose coming out the top. IIRC this was the same routing as my 02 Sierra HD. Never had a problem until recently with either truck losing so much fluid so fast. I am thinking that the dirt and gravel pieces that filled up the trap (little black cap) are the culprit. Once the debris clogged the trap the gases couldn't evacuate normally building up pressure which somehow created a siphon and started sucking the fluid out? Was thinking of turning the trap over and tying it to the inside of the fender liner making it harder for debris to get caught in it. Any thoughts on that?

Matt
jbplock
05-02-2009, 05:43
... Was thinking of turning the trap over and tying it to the inside of the fender liner making it harder for debris to get caught in it. Any thoughts on that?

Matt,

I had a leak like yours once too .. cleaned the cap and all has been well since .. the hose on my 03 was tied to the inner fender liner from the factory.
mattb5150
05-03-2009, 10:02
Hi JP,

You mean the small (.75" dia.) black cap? I am pretty confident that it comes from the factory tied to the fender liner. My point is that it is inverted and hangs below the liner so that it can accumulate debris. I am thinking about tying it up so that the cap stays inside the liner on the engine side and the top of the cap is up with the hose exiting from the bottom so that dirt and road debris do not get trapped inside and cause this problem again. What do you think?

Matt
jbplock
05-04-2009, 16:54
Hi JP,

You mean the small (.75" dia.) black cap? ... I am thinking about tying it up so that the cap stays inside the liner on the engine side and the top of the cap is up ... so that dirt and road debris do not get trapped inside and cause this problem again. What do you think?

Matt, Yes the black cap .. keeping it up and inside the liner is a good idea .. the only concern I would have is that pointing the cap upward could allow water to get in ... maybe increase the length of the hose so the cap is higher in the engine compartment but still pointing downward ??