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

[Jim]

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?

 

[Chris Phillipo]

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?

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

 

[Gilles Gour]

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?

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?

 

[Jim]

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

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.

 

[Chris Phillipo]

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.

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.

 

[Edward Hayes]

Any chance the differential was covered with water?? ed

 

[Jim]

On Mon, 12 Apr 2004 12:51:20 GMT, "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?

 

[Tim]

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

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

 

[Edward Hayes]

The water would be mixed with the oil to make what looks like a brown froth.
I've seen it many times on all makes of cars. ed