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A little more than a month (2300 miles) ago, I was at the dealership getting the Takata airbag recall done. While there, I asked them do some other work (spark plugs, brake fluid), and they talked me into letting them replace the front and rear differential fluids. Shortly after, I noticed a puddle in the garage under the rear of my car, but that was a rainy day, so I didn't think much of it...just assumed it'd dripped off the garage door. Today, I realized it was still there, and it's not rained for a while. So, I parked in the driveway and checked the puddle. It's not water. I got under the Outback and found rear diff fluid all over the underside of the car and a big drop hanging from the bottom plug. I don't own a 13mm allen wrench or male socket attachment, so I can't tighten it...but I tested the bottom plug for tightness and with my thumb and one finger was able to loosen it.

I assume, when they replaced the rear diff fluid, they finger tightened the bottom plug and forgot to torque it. I've been leaking fluid for weeks. I don't see that there's a way short of "drain and measure" to see how much fluid is in there. I suppose the fact that it was still dripping means it's at least not quite dry. :frown2:

It's going back to the dealership tomorrow. I'm just curious if there's any way of knowing if any damage has been done. I assume they'll remove both plugs and "fill'er up" again, and hopefully tighten the bottom one this time...but how many years of rear diff life might I have lost on this screw-up?
 

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2013 Outback 2.5i Convenience
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You won't know unless you know how much fluid was lost. It would have to be mostly empty I think before you have damage. The fluid is thick and coats the gears and bearings well.

Are you hearing any noise or does the car sound normal? No noise is good news.
 

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First - Subaru rear diffs are robust and typically last the life of the vehicle. Subaru rear diff failure is very rare. They easily last the life of the vehicle without even changing the oil. I don't recommend that I'm just saying they don't really fail. Granted we have *ZERO* real data and it is a mechanical part that can fail, but more than likely no big deal.

This is really simple - just look. Drain the oil into a clear and clean pan and look for debris and measure how much oil is in it (keeping in mind there's lots of thick residual oil still in the case). If the oil got low enough to cause damage it would be oil induced wear which will result in metal in the oil. This should be done rather than guessing and wondering and hoping. If they messed up it seems like they'd want to do the right thing and do this simple step for you and show you the oil.

Personally I'd do it myself, I wouldn't want this hanging on 3rd party communication and chains of command of scheduling/calling, customer service, service advisor, filling out forms, and then some tech who passes it to some other tech. Since it appears you can't, politely and with grace ask if they make sure someone does this and follow through.

You can also send the oil off to be analyzed by an oil analysis company that does UOA. I think they're cheap - like $30. You can call the company first and ask them if there test would be a good option here but they measure metal in the oil which is an indicator of internal wear, the only failure mode of practical concern here.
 

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as mentioned - noise is very bad mojo. a failing diff will make noise and it won't be repairable...well not easily or a financially viable repair.
 

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It's going back to the dealership tomorrow. I'm just curious if there's any way of knowing if any damage has been done. I assume they'll remove both plugs and "fill'er up" again, and hopefully tighten the bottom one this time...but how many years of rear diff life might I have lost on this screw-up?
I think you are being overly concerned. Also doubt you lost any years of life from the rear diff.

If it were dry you would know it from the noise coming from the diff.

Tech will torque the bolts, top off the fluid and you will be on your way. No harm no foul.
 

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Discussion Starter #6
I didn't get to see it, but I was told they drained it, "most of the fluid was there", filled it again with new fluid, and used tools to torque the plugs this time.
 

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as suspected carry on, you'll never have rear diff issues. a subaru rear diff needs very little fluid as it's not generating much heat or performing much work like the engine and trans oils.
 
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