Flushing out Subaru Diffs?

[Phishin]

So, I just bought a 2009 Forester.

I just ordered Redline 75w90 Gear Lube and a few tools to help me change out the differential fluids front and rear.

After reading what everyone posts about Subaru diffs, I expect to find some REALLY nasty fluid (full of metal) when I drain them. I assume they have never been changed and this 2009 Forester has 45K miles on the clock. So, I expect something scary to come draining out of them.

What do you guys think about attempting to clean up any residue after I let the diffs completely drain? I want to get as much of this crud out as possible before I pour in the Redline gear lube. Would you all consider it? If so, what should I use?

What I'm thinking of doing is either: A.) Leaving the fill and drain plugs out after the diff's drain, and squirt some fluid all around the inside of the diff's and let them drain again. Or, re-install the drain plug, fill with a fluid, let it sit for a minute, and then let it drain out. Then install my new gear lube.

Good idea? Am I thinking too much?

Lastly, if this sounds like a good idea, what "cleaning" fluid would you use? Some different ideas I have: Supertech (cheap) gear lube, MMO, carb cleaner, Seafoam, PCMO, Kerosene, etc. etc.

Sorry for the wrong post this morning....too much coffee and excited about servicing this Subaru.

 

[Doog]

I would take the car for a 30 minute ride to get the gear oil up to operating temp before draining. That should be sufficient. Flushing is a waste of time IMO. You may want to invest in a magnetic drain plug if it does not have one.

 

[Trav]

You are over thinking this IMO. Doog has it right, get it warm, drain it and refill.

 

[Clevy]

Originally Posted By: Phishin
So, I just bought a 2009 Forester.

I just ordered Redline 75w90 Gear Lube and a few tools to help me change out the differential fluids front and rear.

After reading what everyone posts about Subaru diffs, I expect to find some REALLY nasty fluid (full of metal) when I drain them. I assume they have never been changed and this 2009 Forester has 45K miles on the clock. So, I expect something scary to come draining out of them.

What do you guys think about attempting to clean up any residue after I let the diffs completely drain? I want to get as much of this crud out as possible before I pour in the Redline gear lube. Would you all consider it? If so, what should I use?

What I'm thinking of doing is either: A.) Leaving the fill and drain plugs out after the diff's drain, and squirt some fluid all around the inside of the diff's and let them drain again. Or, re-install the drain plug, fill with a fluid, let it sit for a minute, and then let it drain out. Then install my new gear lube.

Good idea? Am I thinking too much?

Lastly, if this sounds like a good idea, what "cleaning" fluid would you use? Some different ideas I have: Supertech (cheap) gear lube, MMO, carb cleaner, Seafoam, PCMO, Kerosene, etc. etc.

Sorry for the wrong post this morning....too much coffee and excited about servicing this Subaru.




You're thinking too much. Get them hot,drain,fill and roll.
Don't overfill. That's bad.

 

[gomes512]

Flushing will be overkill. Only thing I would add is if it only has a drain plug I stick a small vinyl hose with attached handpump to suck out the residue on the bottom. Helps get that last bit of fluid out that likely has any "big" particles that settled on the bottom.

 

[krismoriah72]

Magnets on the drain plug are your friend. The fluid should be clean and clear at only 45K miles.

Get warm, drain, clean magnets, fill, chill for another 50K

Save your money for wheel bearings, axles and head gaskets.. this subaru will last you a very long time.

 

[i812]

The drain plug has a fairly good size magnet built-in. Just drive, drain, and refill. I have used Eneos gear oil in the past and now use Subaru Extra "S" with no issues. I purchase the Extra "S" 4 quarts at a time from the dealership using a recycled oil gallon container.

 

[drolds]

I second the magnetic drain-plug. If you want to flush the differential, just do a warm-up drive and drain the differential oil. Then spray into the fill plug hole w/ a can brake cleaner. It will loosen and drain out gum and varnish and then evaporate- you don't want a flushing chemical to stay inside the differential.
If the stock drain-plug is not magnetic, you could replace it very quickly before you lose much old fluid with a magnetic plug. Then drive the car to operating temp and then drain completely and clean off the metal debris from the new magnetic plug. Then use the brake cleaner, drain that & re-install new magnetic plug, fill w/ new fluid and presto- you have accomplished your goal.

Dr. Olds
1994 Intrepid ES 3.5 V6 Amsoil 10w30 SS, Amsoil ATF, Amsoil 75W-90 Severe Gear in Diff.
1969 Olds Toronado 455 W34 Rotella 15w40

 

[Phishin]

Originally Posted By: krismoriah72

Save your money for wheel bearings, axles and head gaskets.. this subaru will last you a very long time.


I just didn't blindly buy this car. I'm pretty sure these old known Subaru issues were settled by 2009. The wheel bearing problem and HG issue for sure. Am I wrong?

Not sure about Subaru axles...but any CV axle is gonna need replaced sooner or later.

 

[gathermewool]

The HG's are enough of a concern that SOA still recommends (at least they still did when I asked for my '08 STI) the coolant conditioner be added to the coolant when it's drained and refilled per the maintenance schedule. With revised gaskets out in the fleet by the early-to-mid 2000's (IIRC,) I believe the incidents of failure has dropped significantly in recent years. It takes a while to Gage when the problem was resolved, because it usually wasnt a high risk until well more than 100k miles are accumulated (the HG went in my '97 Legacy for the previous owner at ~160k miles - I purchased post-repair at closer to 175k.)

Back on topic:

I saw some dark gray FF fluid come out of my STI rear diff at around 30k miles (search here for my used oil analysis) that looked pretty nasty, but the color seems to be normal for a Torsen LSD.

Your open differentials are pretty low-stress applications, to be honest. If you plan on using a version of RL's Shockproof, let me suggest you try something a little lighter and less heavy duty. For the money, choose any name-brand gear lube, like Valvoline or Mobil 1 less than $10/quart, instead of closer to $20 for boutique oils.

Motul Gear 300 was about the best I could find, on paper, but realistically it was overkill in my STI for how I drive (even with the occasional romps and one auto-x event I took part in.)

As for getting out as much of the factory fill as possible I found a small syringe in Wal-Mart that had a long, curved nozzle that worked perfectly for sucking out just about every last bit in the pumpkin. It was only a few bucks, too.

Some additional notes:

Buy a decent hand pump. I bought a NAPA pump - the type you pull back the plunger to suck up the oil and then depress to inject into the diff - for my first change and it was only ok. It leaked through the seal some, which made a bit of a mess. The second time it leaked more than it pumped - a disaster!. I then bought a pump that works like a soap hand pump that worked perfectly and any leakage could be directed back to the what bottle it was inserted into.

Finally, make sure to loosen the fill plug before the drain. I didn't have any issues using a breaker bar, but it was tougher than I expected and took me forever to just lean into it and break it free.

Finally, the drain plug is magnetic, so don't worry about changing it for something aftermarket.

If you have any questions or can't find my FF drain thread, message me and i'll find it for you.

 

[SHOZ]

On my Genesis Coupe 6 sp manual trans I had Redline Lightweight Shockproof. It's a aqua colored oil. I drained it and added some new Redline MTL. Drove it for a week and drained it again. You couldn't even tell I drain the original aqua colored oil out.

So I filled the trans with some paint thinner (naphthalene) and with it jacked up shifted through all the gears at idle for about 10 minutes. Drained it and left the drain plug out overnight.

I don't know how I would have ever got the shockproof all out any other way.

 

[Phishin]

Originally Posted By: gathermewool

Your open differentials are pretty low-stress applications, to be honest. If you plan on using a version of RL's Shockproof, let me suggest you try something a little lighter and less heavy duty. For the money, choose any name-brand gear lube, like Valvoline or Mobil 1 less than $10/quart, instead of closer to $20 for boutique oils.


I'm not using the heavy Shockproof. But I did order 6 quarts of RL's regular 75w90 where GL-5 is called for. I know I went a bit overboard getting the RL lube, but it's okay. Mobil is about $12/quart anyhow. Valvoline $10. I could splurge a few dollars for the RL, so I did.

Besides, I had to order a T-70 Torx bit anyhow....so it was "easy" to just add the RL to the cart, along with a metal flexible neck funnel...thanks to Amazon.

 

[FutureDoc]

Just drain and fill a warm diff... there really is not a system to "flush". Just wipe the mag-plugs, drain, fill and go.

The Turbo models did not have common HG issues.

Wheel bearing should be fine, and the CV are a bit more complicated as "user error" from non-alignment, off-tire size and some other lack of maintenance on the drive system can cause problems.

If you want to see bad diff fluid in a Subie, see this:

 

[BHopkins]

I would worry that if you put any type of cleaner in the transfer case, that you would not be able to get it all out, and residual cleaner would break down the fresh differential fluid. It seems that you are much better off with any left over old differential fluid, with whatever small amount of contaminant that may be in there, than you would with cleaner in the new fill.

 

[artificialist]

What I do is:
1. Drain the factory fill
2. Run some basic gear oil for 1,000 miles
3. Drain that basic gear oil and put premium gear oil in.

 

[JTK]

Phishin, if you really want to, buy a bottle of the least expensive 75w90 you can find, heat it up in a hot water bath while your taking the car for a drive (to warm it up) and run it through the rear diff of your new to you Soob for a flush. Like said, the drain plug will have a magnet and it will have a glob of crud on it.

I'm not positive if the 4EAT AT takes gear oil for the front diff (pretty sure it does), but for what ever reason, you don't hear of that oil being nasty on drain-out like the rear is. I'd do it anyway.

Either way, make sure you break that fill plug loose first, then the drain. That can be the hardest part(s).

 

[SOHCman]

Originally Posted By: artificialist
What I do is:
1. Drain the factory fill
2. Run some basic gear oil for 1,000 miles
3. Drain that basic gear oil and put premium gear oil in.


This

And drain it hot before the slime settles. Cleans a diff right out.