2014 GT oil blowing out diff vent - how to fix it?

[Dougmore]

I purchased my 2014 GT brand spanking new in August 2014. It currently has about 44,000 miles on it. Stock 3.31 limited-slip rear end.

Any idea why a 100% street-driven car would blow oil out the diff vent and what I might do to stop it? If I was tracking the car, I could understand, but it's never been on a drag strip, let alone a road track. I've never done a donut with it. I've never made tire smoke. The tires do break loose frequently, but I don't spin them on and on. I'm an old fart and don't like to buy tires. 44,000 miles and I'm about halfway through my second set.

I took it in twice under warranty for an oil puddle in the garage under the rear diff the first year I had it. It was blowing out the vent tube. I don't remember what they said they did the first time - seems like they just added fluid and asked me if I was tracking the car. The second time, they said they drained and replaced the oil with new oil plus the additive - in case the factory installed the wrong stuff, so they said. No more puddles; I thought all was well.

6 years later, I've never had a single drip from the car on the floor.

When I was running the Boost-a-Pump vacuum line for my blower install last year, I noticed a ton of grease all over the gas tank. It was coming from the diff overflow. I'll bet the Ford "technician" relocated the overflow so it would drip on the gas tank instead of on my floor.

Now it's on the lift for its first oil change since then (less than 2000 miles), and since it's up on my shiny new lift, I decided to check the diff fluid. It's real low. I can't touch it with my pinky.

 

[SilBult]

I am a pretty old guy myself [ 77] and I also have a '14 GT that I bought new. I've got a little over 83,000 miles on mine, mostly stock. A track key, oil catch can and some suspension mods for an occasional autocross and winding rural roads. I also had some rear end oil blowing out of the axle vent. Not really bad, but annoying. Ford has a TSB about this and I ordered the kit from my local Ford dealer where I have a discount. It consists of a fitting to replace the one on the axle tube and a rubber hose with a vent cap on one end. You connect the open end of the hose to the new fitting on the axle and you mount the new vent cap to the top of the diff. It's worked fine for me. No more mess and no loss of oil.

 

[Juice]

Mine had a damp left axle tube.
Installed trackpack finned diff cover. Moves vent to top center of cover. Plugged vent on axle, problem solved.

 

[WJBertrand]

There are aftermarket catch reservoirs that are mounted well above the axle that catch the overflow and let it drain back into the axle. Mine barfed oil out the breather on the left axle tube too. I suspect this occurs during hard right turns. I fitted a JLT axle reservoir
https://lmr.com/item/JLT-AX05/JLT-R... DSA&utm_term=/item&utm_content=Product Pages
but later installed a finned cover with a central top vent.

I capped off the axle vent and moved the check valve to the top center of the new cover. I left the expansion tank connected to it since it was already installed.

 

[Dougmore]

It looks like my car either came with that Ford vent kit or the stealer installed it one of the two times I took it in. They have the vent end clipped to the gas tank strap at the rear of the gas tank right up against the floor pan. The entire gas tank is covered in oil. But hey, they didn't get another warranty comeback, eh? I'm betting they installed it correctly the first trip, then moved the vent end up over the gas tank on the second trip. A$$holes!

There's no reason the gear oil should get that hot in a street-driven car. It does see 80-85 mph on the freeway regularly, which is what it takes to keep up with traffic around here. But still, that shouldn't cause 3.31 gears to heat up. I wonder if it was set up poorly at the factory. I've driven stick-shift cars all my life, including a '69 Torino and 69' Mach I, which didn't have near the sound insulation this one has. I've never had a rear-end klunk as much as this one does if it's not shifted just right.

I hear some noise when coasting that I'm hoping I'm just noticing because I think the diff is empty. It's not something any normal person would detect, so I hope it's just my paranoia and I don't have to get the thing rebuilt.

Anyway, I'm going to buy/build a reservoir for it. I'll probably replace the diff cover with the Steeda finned knock-off.

 

[WJBertrand]

It looks like my car either came with that Ford vent kit or the stealer installed it one of the two times I took it in. They have the vent end clipped to the gas tank strap at the rear of the gas tank right up against the floor pan. The entire gas tank is covered in oil. But hey, they didn't get another warranty comeback, eh? I'm betting they installed it correctly the first trip, then moved the vent end up over the gas tank on the second trip. A$$holes!

There's no reason the gear oil should get that hot in a street-driven car. It does see 80-85 mph on the freeway regularly, which is what it takes to keep up with traffic around here. But still, that shouldn't cause 3.31 gears to heat up. I wonder if it was set up poorly at the factory. I've driven stick-shift cars all my life, including a '69 Torino and 69' Mach I, which didn't have near the sound insulation this one has. I've never had a rear-end klunk as much as this one does if it's not shifted just right.

I hear some noise when coasting that I'm hoping I'm just noticing because I think the diff is empty. It's not something any normal person would detect, so I hope it's just my paranoia and I don't have to get the thing rebuilt.

Anyway, I'm going to buy/build a reservoir for it. I'll probably replace the diff cover with the Steeda finned knock-off.

I think it barfs out the axle vent because of sloshing, not heat expansion. In a hard right turn, the axle lube will slosh over to the left axle tube, reaching the level of the vent on that tube. I’ve heard some vents are installed on the right side tube, in that case the dynamics are reversed and a hard left would be the problem.


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[Suecra]

Its normal unless its just excessive. When I built my rear axle it looked like it had a lot of blowby but I bought a new insert when it was taken apart and it hasnt had any issues leaking out. If replacing the plug fixes it then its fairly cheap option.

 

[TerryZak]

Just picked up a 2010 V6 for my son and have the differential out of the car for a rebuild. The axle tube by the vent was built up with sand/dirt from on going vent leakage. Through my AllData-DIY subscription found three Technical Service Bulletins for gear oil leaving the vent on acceleration. If that can happen on a V6, then I'm sure it can happen on the V8's.

In the final service bulletin there's specificaion for a replacement vent, P/N AR3Z-4A058-B. I'd go with that before I plugged the vent. I got mine from the local Ford dealership, and was surprised to find that Amazon has it listed.

TSB 10-3-7, 03/01/10, REAR DRIVE AXLE VENT - OIL LEAK
TSB 12-2-1, 02/03/12, REAR DRIVE AXLE VENT - OIL LEAK - BUILT ON OR BEFORE 1/23/2012
TSB 12-5-8, 05/29/12, REAR DRIVE AXLE VENT - OIL LEAK

 

[Dougmore]

Fluid leaving on acceleration. I didn't think about that. My car does plenty of accelerating to the traction limits.

I don't think the turkey baster bulb stuck right on the axle tube will hold near enough fluid. My vent tube outlet is as high as it can go now and still be under the car. It's right up against the floor pan at the gas tank strap. I can't imagine oil can slosh up that high on cornering; it has to be heat-related. I'll know for sure how much oil is gone once I pull the cover, but it's probably down about a quart, judging by how much is on the gas tank. The entire gas tank and skid plate(?) is covered in oil. I wonder if maybe the vent outlet is jammed up against the floor pan causing pressure to build up until it eventually erupts out the valve.

I ordered a GT500 finned aluminum diff cover and the JLT catch can.

I'm thinking if I route the hose from the top of the new diff cover, maybe it'll be better than from the axle tube. Any opinions? It oughtta at least rule out cornering issues.

 

[WJBertrand]

Agreed, don't just cap it off unless you've provided an alternative vent such as on a different cover. If pressure is trapped in there blown seals will result.

 

[13v6]

Do what TerryZak said and exercise the TSB fix. This is an old/known problem.

 

[Dougmore]

Do what TerryZak said and exercise the TSB fix. This is an old/known problem.

My car has had the hose and plastic valve fix since new, or since slightly after new when I took it in for the leaky diff. The hose goes from the left axle tube and is clipped to the gas tank strap right up against the floor pan. I didn't think the turkey baster would be big enough to contain the fluid, but that was before I wondered if the vent valve might be stopped up against the floor pan. Maybe I should have tried the bulb, but the spendy parts will be here tomorrow.

If the photo uploads, the green circle is around the end of the vent hose. It's crammed in the corner up against the floor pan. There is the usual plastic valve on it. The pink arrow points at the clip on the gas tank strap that's supposed to be clipped to the top of the diff housing. It's a greasier mess than the picture indicates.

 

[Juice]

The finned cover and moving the vent to the top of the cover is the best and simplest solution. No catch can, no vent hose, and no leaks open tracking/HPDE. Looks good, provides diff cooling, and easy drain/refill access. I was toying with the catch can idea, but the cost of those was dickriculous.

 

[mattjames]

I doubt it's down a quart, but what also can help along with the center venting cover, is looping the line high, like they tried, but also routing it back down so it'll vent, but not let fluid out.

 

[Juice]

I doubt it's down a quart, but what also can help along with the center venting cover, is looping the line high, like they tried, but also routing it back down so it'll vent, but not let fluid out.

On the street, yes, high vent works. Open track, no.

 

[Suecra]

On the street, yes, high vent works. Open track, no.

Well if your tracking the car unusual things can happen like this, which is why tracking the car usually means more maintenance. There should be a fill hole on the backside of the diff and I would just check it when you inspect the car after a day at the track, its unlikely to lose that much fluid in one day even with hard cornering and a lot of pressure/ventilation happening.

 

[Juice]

Well if your tracking the car unusual things can happen like this, which is why tracking the car usually means more maintenance. There should be a fill hole on the backside of the diff and I would just check it when you inspect the car after a day at the track, its unlikely to lose that much fluid in one day even with hard cornering and a lot of pressure/ventilation happening.

My point was with eliminating the issue of diff leak, that is one less item I need to worry about prepping for an HPDE event. I dont check my diff fluid. No need as seal replacements force fluid change anyway.

 

[Dougmore]

Final (I hope) report on my diff leak. $400, but it's fixed!

I installed the JLT catch can ($120) and Ford finned diff cover ($200), with a LubeLocker gasket ($25), a few weeks ago. As much oil as was all over my gas tank, I drained exactly 2 quarts when I did the diff cover, so no worries about low fluid. I put in two quarts of Royal Purple and no additive ($60). It's not making any noise on tight turns, so I'll hold off on the additive.

I plugged the hole in the axle tube and routed the catch can hose to the top vent on the diff cover. I shortened the hose and routed it directly to the fitting without going around the panhard support like the instructions say.

So far, all is well. I think my diff leak is solved, no thanks to dealership mechanics. I'd post a photo, but my Chevelle is up on the lift for some transmission sealage and I don't feel like moving cars around again.

I want to thank everyone who took time to reply to my original post. It's great to bounce these things off a group of like-minded gearheads.

 

[JEWC_Motorsports]

You need the additive, not enough of it in RP.