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Why would rear differential overflow after 7 yrs/111k miles

Recently I found small puddles of gear oil beneath the rear differential on my '97 Legacy wagon. There was a fair amount of gear oil around the casing, so I took it in for a diagnosis (I'm not much of a DIY'er). The diag- nosis was that it had come out the overflow hole and that there were no leaks. The service rep said it must have been overfilled.

I don't specifically recall ever servicing this differential, but if it was part of a recommended routine service it was done. Certainly not in recent memory.

SO my question is why it would overflow after such a long time. Also, it appeared this happened 2 or maybe

3 times, and then it had bled off enough so there was no more draining.

This may have happened initially after pulling into the garage after a long highway trip. But I take a lot of these, some in the heat of summer and it's never happened before.

Can anyone explain why now?

Reply to
Jim
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The next time you drive it, stop and check if the differential case is getting hot.

Reply to
Chris Phillipo

Rear differentials are impossible to overfill. The fill hole is horizontal and the prodedure asks to fill up flush with the hole's bottom side. Mechanics usually fill until the oil starts to overflow. Put anymore in and it will immediately leak to the ground. Did they open it to check the oil level?

Reply to
Gilles Gour

Should it not be hot? Would that be indicative of an internal problem?

And how hot would be too hot? Hot to the touch?

Thanks.

Reply to
Jim

If it's hot it may have boiled the oil which would force some out the vent hole. It could be hot due to a failed bearing, unequal tire diameters or dragging brakes.

Reply to
Chris Phillipo

Reply to
Edward Hayes

Not submerged, no. I drove through some puiddles the day or two before, but nothing more than a few inches deep.

Would gear oil float on water like light weight oils? Or vice versa?

Reply to
Jim

not so much the oil floating, just that if you made a "water crossing", especially with the differential at operating temperature, deep enough to cover the vent, water could be sucked into the diff. if enough was sucked in to fill it, oil would be forced out eventually. that is the way to "overfill" a diff, ie, through the vent tube. not sure about subaru, but many diff. vents have a check valve to prevent this.

tim

Reply to
Tim

Reply to
Edward Hayes

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