Rear Diff Factory Fill Come Out Grey Nasty?

[gathermewool]

I can't find the threads with the pics here at work, but, in my search for the perfect rear diff fluid, I've come across a few pics of people pouring out some really nasty initial fill fluid from their rear diffs. Most people online and a few people I've asked have stated that the OEM fluid just doesn't cut it, that the color is due to bearing and break-in material. Fewer people have told me that it's just the color of the OEM fluid or some additive.

I'm inclined to believe the former since the concensus online is that the factory fill for the 08 STI is Go Extra S Gear Oil. Far be it from me to state internet chatter as fact, though.

Also, the Subaru maintenance schedule simply states to inspect the diff fluid at 30k and again at 90k. There's no replacement scheduled. I know a lot of people have never replaced their diff fluid or maybe wait until >100k, but I've got a higher performance setup. I don't really beat on the car and my track days will be kept to a minimum, though, so the whole high performance "need" for a high performance gear oil may not be justified... I'm going to replace the fluid for peace of mind if nothing else, but these things interest me, and I'd rather find out the truth than just listen to people telling me that what's in there now is hurting my diff, that the only way to make it better is to spend $25 for Motul or $18 for Amsoil gear oil. While this really isn't that much to spend for peace of mind I'd like to know the truth. Also, I'd like to know if THIS change using high-end fluid can be a life-time fill. I do plan to keep the car for a life time. Thanks for any input!

 

[unDummy]

Define lifetime? yours are the car? or car payment length? or warranty time?

If its a vehicle you plan on keeping forever, and hand it down to the children, grandchildren, nieces and nephews, or other family member....... then definitely start a maintenance program with reasonable intervals and teach those around you to do the same.

Gear oil, IMO, should always be changed in 30k, 2-3yrs intervals...time or mileage whichever comes 1st. Brakes should be bled yearly, or minimally every 2 yrs, and at every brake job. Coolant, hoses, belts, filters, PSF, plugs, and other miscellaneous parts have a life time too!

Every component has its life time. Do you want that life time to be 3yrs/36k or whatever the warranty is? Do you want that life time to be 60-72 months or whatever the financing is? Or do you want to be on a commercial for that automaker when you hit 1 million miles?

 

[c3po]

I changed my Diff Fluid in my Marauder at 15,000 miles and it came out looking nasty, it had a grey color, probably from the break in metals.

I think anyone who buys a new car should probably change the Diff Fluid out at about 10,000 miles or so.

 

[Herz]

changed the factory fill in my sierra at 100K and it was pretty nasty. I did keep it topped off though.

 

[gathermewool]

I'm at just over 16k, and want to do this. I'm debating whether to get the fluid analyzed. I think the data-whore nerd in me will prevail, but who to send it to and what to analyze for is another question. From what I've seen TAN is a must. Anything else? Terry would be best, but he didn't recommend analysis, and $99 is a bit expensive for something like this...

Originally Posted By: defektes
changed the factory fill in my sierra at 100K and it was pretty nasty. I did keep it topped off though.


How much did you have to top it off? Was there a small leak?

 

[Herz]

hmm not much maybee half a quart in its 100k lifetime. every 3 or 4 oil changes i'd have to pump a little in to keep it full. Ever since I put valvoline syn in it the gear oil doesnt drop nearly at all anymore.

 

[Kestas]

Someone once posted that most of the diff break-in happens in the first 3K. The fluid should be initially changed at 3-5K, then use whatever interval you want after that. I use 30K for regular fluid, 60K for synthetic.

 

[gathermewool]

What about for a crem de la creme, boutique oil like Motul or Amsoil? If regular use diffs are going 200k+ miles then what's to say mine can't go 200k+ on a fantastic gear lube?

 

[webfors]

Change the FF fill diff on the subie. They shed metal like crazy the first few thousand miles. Here's mine after 10k miles:

http://sugar.webfors.com/gallery/gearllube

The fluid was a nasty grey muddy soup and the magnet was *FULL* of metal shavings. No way that should be in there past 10k miles, let alone 90k

No analysis needed imho.

After the FF I ran Motul Gear 300 for 25k miles and it came out as golden as when it went in without a single shaving on the magnet. That tells me everything I need to know, and is probably good for double that mileage. What's $20 every 30k miles to know your diff won't blow up right after warranty? It's an easy job to change too.

 

[webfors]

Click the images two times, and you'll get the super close up of pic # 2 to see the shavings. It'll bring tears to your eyes

Pic #7 is pretty much what the magnet looked like after 25k miles on Motul Gear 300. Proof is in the grey pudding

 

[gathermewool]

Originally Posted By: webfors
Change the FF fill diff on the subie. They shed metal like crazy the first few thousand miles. Here's mine after 10k miles:

http://sugar.webfors.com/gallery/gearllube

The fluid was a nasty grey muddy soup and the magnet was *FULL* of metal shavings. No way that should be in there past 10k miles, let alone 90k

No analysis needed imho.

After the FF I ran Motul Gear 300 for 25k miles and it came out as golden as when it went in without a single shaving on the magnet. That tells me everything I need to know, and is probably good for double that mileage. What's $20 every 30k miles to know your diff won't blow up right after warranty? It's an easy job to change too.



I'm still deciding between Motul 300, Amsoil Severe Gear and Redline, but if I do change out to one of these boutique oils I don't think I'll change it again for another 60-90k. If Subaru thinks the factory fill only needs to be inspected at 30k and then again at 90k I think changing to a high quality gear lube should be fine for AT LEAST 90k. I've got 2500 miles until my next oil change, which will put me at 19k on the odo - plenty of time to decide : )

 

[webfors]

Originally Posted By: gathermewool
If Subaru thinks the factory fill only needs to be inspected at 30k and then again at 90k I think changing to a high quality gear lube should be fine for AT LEAST 90k.


"should be fine" is the $2000 question (aka: cost of a new diff). With a quality syn gear lube I would be comfortable with 50-60k max in the rear diff. In the subie 5mt, this diff is under pressure 100% of the time. It's not like my crv which would turn on the back wheels a few times a year in the winter... and even that diff had to be changed as per a TSB after the first year due failing/contaminated fluid which caused a slight grinding noise when turning.

Just make sure to check it periodically if you want to run it out further. Don't assume anything.

 

[gathermewool]

Look, we both know I'm full of it. I'm having a hard enough time running extended OCI's. As much as I want to I probably won't be able to go any longer than 50k before my little tick kicks in, forcing me to change it out

 

[webfors]

I'm right there with you. I like the 'idea' of extending fluid life, but my 'issues' won't allow me to push the limit too far

 

[LoneRanger]

I have a really dumb question. If you drive the car long enough to get the rear diff hot before you change the fluid, does it run out like oil via gravity draining when you remove the plug or do you need an oil puller to get it all out? And does the new gear oil pour in or do you have to squirt it in like grease?

 

[webfors]

75w90 gear oil is low viscosity, similar to motor oil. Assuming a Subaru rear diff, you remove top plug, then remove bottom plug and it pours out like motor oil via gravity. Wait a few minutes and it's all out. Put bottom plug back in (put some sealer on it first), pour the new gear oil into the top plug/hole until it starts pouring out the hole then put sealer on the plug threads and screw it back in.

Motul Gear 300 comes with a long built in spout, so you insert the spout into the top hole and squeeze the bottle until the gear oil starts pouring out of the hole and reinsert the plug. Real easy procedure.

The dealer here charges $69 + tax to do it. So spending $20 for the gear oil and doing it myself is an inexpensive alternative, but with a premium synthetic gear oil. So you win!!

 

[chad8]

Originally Posted By: LoneRanger
I have a really dumb question. If you drive the car long enough to get the rear diff hot before you change the fluid, does it run out like oil via gravity draining when you remove the plug or do you need an oil puller to get it all out? And does the new gear oil pour in or do you have to squirt it in like grease?

not dumb at all. Gear oil is usually 75-90 wt.grease is double or triple that. It will drain on its own but s-l-o-w-l-y unless it has broken down from wear. some diff have 2 plugs, a drain plug and a fill plug. remove both and it will drain much faster or run an air hose up to the top one and blow it out. If the lube gets stuck inside (bad news) and plugs the hole, get a screwdriver in the hole and wiggle it around to clear the obstruction.That is really a good question.

 

[gathermewool]

Well, I just drained the fluid and it came out dark grey. I've asked and every one gives me the same reason I give for why some motor oils turn darker faster, that motor oil color means very little. They keep saying color means nothing, but does this hold true for a gear-only-type LSD - no clutch material.

I guess if the excuse that the oil turning color is due to wearing out, what would cause the rear diff fluid to turn dark, dark grey in 17k miles, but remain golden or amber through subsequent changes.

 

[tom slick]

This is my experience with "lifetime fill" differential oil

https://bobistheoilguy.com/forums/posts/1169708/

 

[Ben99GT]

I waited ~140,000 miles before changing the "lifetime fill" in my 01 F150. My fluid looked like that, only worse, and had a nice varnish coating everywhere.

I'll never do that again.