Service Interval for Rear Diff and Coolant

[Bee8point5]

Does anyone know the "official" Audi numbers for these as well as what the people in the know really think?

[Spawne32]

officially? audi claims its lifetime. In reality? 100k on the coolant, 65-75k on the differential fluid, sometimes sooner depending on how its being used. Open differentials tend to be a bit easier on the fluid.

[JayDog747]

Gear oil and hydraulic fluid(A/T-P/S) should be changed every 50k miles. Coolant should be replaced every 5 years regardless of miles. Brake fluid should be changed every 2-3 years regardless of miles.

[elscotto80]

Gear oil and hydraulic fluid(A/T-P/S) should be changed every 50k miles. Coolant should be replaced every 5 years regardless of miles. Brake fluid should be changed every 2-3 years regardless of miles.

These are good numbers to go by.

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[Spawne32]

These are good numbers to go by.

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In 1957.

[elscotto80]

In 1957.

Then what say you?

[Theiceman]

In 1957.

yeah just what i was thinking .. modern fluids dont need to be changed nearly that often. i will agree on the brake fluid though. and only to keep the bleed nipple from freezing to the caliper.

[Theiceman]

i changed my coolant at 220K km when i rebuilt the engine. looked like brand new. although visual i admit doesnt tell you much . i remember the old green prestone days, you coould definitely tell when it was beat.

[Kolbenringe]

Then what say you?

At the least, we all have access to cheap brake fluid testers, which is what the dealers now use. When there's a certain moisture content reached in the fluid, then they replace it. If the fluid boiled enough to create gas pockets, there's another reason, or if the pedal generally is soft.

Coolant also has testers available. They are now going quite a long time.

We're not in an era anymore where we could pollute and waste. It's not only expensive, it's not environmental, nor does it make sense in many cases.
.
Of course, manufacturers of these products would push unnecessary changes.

[ps2cho]

i changed my coolant at 220K km when i rebuilt the engine. looked like brand new. although visual i admit doesnt tell you much . i remember the old green prestone days, you coould definitely tell when it was beat.

This. The KEY to the coolant going a long time is NOT USING TAP water for any top offs. This is what causes corrosion. Zerex is the OE manufacturer and the blend is specifically designed for the iron block and aluminum heads.

The factory corrosion inhibitor package is typically good for 100k or 10-years. If tap water has ever been introduced it’s a crapshoot. Don’t even flush the system with a garden hose because you’ll never get all the tap water out.

Rear diffs are just opinion. Most cars in the road never change them and it’s “not common” to see diffs getting replaced frequently. For diffs anywhere between 50-80k is probably fine.

[A4x]

I would argue that the front diff fluid should be replaced MORE often than the rear due to its proximity to the exhaust downpipe and transmission. This fluid gets much hotter much faster than the rear fluid, causing it to break down faster. I changed both the front and rear diff fluid around 60k miles and the front looked much worse.

[Spawne32]

Then what say you?

It's 10 year 150,000 mile coolant, changing it at 100,000 miles is merely for peace of mind. The transmission fluid is the sore spot on these cars, which really needs to be serviced every 50-75k in that range, the differentials like I said, 65-75k.

[Spawne32]

I would argue that the front diff fluid should be replaced MORE often than the rear due to its proximity to the exhaust downpipe and transmission. This fluid gets much hotter much faster than the rear fluid, causing it to break down faster. I changed both the front and rear diff fluid around 60k miles and the front looked much worse.

Your right yes, but without having it properly tested its hard to say that just because it looks worse that its in any way "bad" or broken down where its ineffective. It's not subject to the same stresses as other fluids throughout the car or nearly the same amount of heat being generated. The brake fluid I would argue you could go 4-5 years without requiring a flush, but that being said, "requiring" is being used loosely because it probably will go alot longer given that DOT4 is a modern day synthetic fluid. It's the fact that all brake fluid is hygroscopic and can absorb upwards of 2% moisture for its given volume from the atmosphere, which can cause corrosion and breakdown of seals inside the brake system. But lets be honest here, 90% of cars on the road are driving around with the brake fluid never being changed a day in their life. What I have made a habit of doing is when I do brakes I bleed some fluid out using my power bleeder.

[porwal22]

I run BMW Extended Life Coolant in all of my cars, and motorcycles. Looks like washer fluid when it is mixed, but corrosion is nonexistant, even after 10 years.

[Spawne32]

I run BMW Extended Life Coolant in all of my cars, and motorcycles. Looks like washer fluid when it is mixed, but corrosion is nonexistant, even after 10 years.

I'm running CAT ELC Extended life, good for something like 2-300k miles and like 6 years on industrial service use for like a Caterpillar engine. lmao I think I have 5 gallons of fleetgard as well but its blue so I wont use it.

[Theiceman]

i use gravity method. gives me an excuse to have a beer and watch it.. and convince everyone i am ding a critics function to my car ...... so bring me another beer already.

[Spawne32]

i use gravity method. gives me an excuse to have a beer and watch it.. and convince everyone i am ding a critics function to my car ...... so bring me another beer already.

lol this is also a great method

[Kolbenringe]

What I have made a habit of doing is when I do brakes I bleed some fluid out using my power bleeder.

I just got a pressure bleeder and I will never go back to the old school method. The quality of bleed was evident in the pedal feel. The fluid was likely in need of changing anyhow, but the last couple of times I was at Audi, they tested it for moisture and it passed. I drove home from Norway last month, braked numerous times on the Autobahn on the way home from 250kmh to under 100 at points, and it definitely boiled the fluid, leaving a soft pedal. The power bleeder did the trick, saved time, and also I ran the output test on the pump through VCDS. Now I can feel the bite from just a couple of degrees of pedal travel. I also used TRW 5.1 because it was cheap on Amazon Prime and supposedly has a longer service life. The remainder goes into my mountain bikes.

[elscotto80]

It's 10 year 150,000 mile coolant, changing it at 100,000 miles is merely for peace of mind. The transmission fluid is the sore spot on these cars, which really needs to be serviced every 50-75k in that range, the differentials like I said, 65-75k.

Fair enough, good points.

I know some of the fluids will last a bit longer but I like the peace of mind by changing some a little more frequently.

I've only had one coolant flush when my water pump took a crap. Brake fluid 2-3 years. I think my rear diff was changed at 80k, I'm now at 128k, so plenty of time for that one.

I have a manual trans, last fluid change was around 90k I think. No need to mess with that anytime soon.

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[Bee8point5]

Front diff fluid? Gulp? Sorry run that by me again but isn't the front diff lubricated via/through the transmission fluid?

Sorry if you guys want to laugh but I honestly don't know the answer.

[A4x]

Front diff fluid? Gulp? Sorry run that by me again but isn't the front diff lubricated via/through the transmission fluid?

Sorry if you guys want to laugh but I honestly don't know the answer.

If you have the 8 speed automatic transmission, the front diff shares the same housing as the ZF8HP transmission but internally it uses different fluid and there are seals to keep the diff fluid separate from the trans fluid.

EDIT as a result of the great post from elscotto80 below: If you have a manual transmission, the front diff shares the same fluid as the rest of the transmission.

Just another reason 6MTs get better gas mileage, less frictional losses from the additional seals.

The front diff is more critical to change the fluid because it runs MUCH hotter than the rear diff fluid! Transmission and exhaust/turbo are in close proximity which heats the oil quite a bit.

DIY for front diff:
https://www.audizine.com/forum/showt...2#post13055402

DIY for rear diff:
https://www.audizine.com/forum/showt...?highlight=DIY

[elscotto80]

I would argue that the front diff fluid should be replaced MORE often than the rear due to its proximity to the exhaust downpipe and transmission. This fluid gets much hotter much faster than the rear fluid, causing it to break down faster. I changed both the front and rear diff fluid around 60k miles and the front looked much worse.

For those with manual trans, the front diff share the same oil as the trans. It's not separate like it is in the auto.

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[Kolbenringe]

I noticed DAP never did a follow up to the Stronic oil change where they changed the gear oil for the trans and diff. Anyone do that change themselves?

[BrianVan]

Front diff fluid? Gulp? Sorry run that by me again but isn't the front diff lubricated via/through the transmission fluid?

Sorry if you guys want to laugh but I honestly don't know the answer.

Front, rear and center are all independent. (With the auto 8 speed) rear is easy. Front is not bad. Center. Need a lift' or 3 foot jacks.(Lol) Front and rear each take a quart of any GL5 rated oil.

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[Kolbenringe]

So then for clarity with the STronic 501:

-gears, center, and front diff use gear oil
-clutches and mechatronic use the DSG oil

People change out the DSG oil and think they got the transmission.

[Spawne32]

Well the DSG oil is the transmission fluid in those. They are essentially manual transmissions with electronic servos to move the clutches, etc. What people don't realize is that the front differential is not being lubricated by the same fluid, where as that is the case on some other cars and designs.

[Kolbenringe]

Well the DSG oil is the transmission fluid in those. They are essentially manual transmissions with electronic servos to move the clutches, etc. What people don't realize is that the front differential is not being lubricated by the same fluid, where as that is the case on some other cars and designs.

Please don't make it nore confusing thsn it is. There's a reason why people are having trouble and even DAP suspected their S4 hat ATF instead of DSG fluid, probably because someone had the same explanation. Watch the video about it fron DAP. This is not a one-off probably because people want to make the explanations overly complicated and get their own 2 cents in.

[Novarider]

I need to do the fluid on all 3 of my diffs. The front and rear look super easy. Is there a DIY for the center diff?

[Spawne32]

Please don't make it nore confusing thsn it is. There's a reason why people are having trouble and even DAP suspected their S4 hat ATF instead of DSG fluid, probably because someone had the same explanation. Watch the video about it fron DAP. This is not a one-off probably because people want to make the explanations overly complicated and get their own 2 cents in.

Post the video, but I don't understand your meaning, the S4 doesnt have ATF, it has DSG fluid. I've watched that video, it clearly explains that. DSG oil is green, what they did explain was that it was important to make sure that you are using t he correct fluid if your using audi fluid, because the bottles look all the same.

[Kolbenringe]

Post the video, but I don't understand your meaning, the S4 doesnt have ATF, it has DSG fluid. I've watched that video, it clearly explains that. DSG oil is green, what they did explain was that it was important to make sure that you are using t he correct fluid if your using audi fluid, because the bottles look all the same.

You're doing it again.

[Spawne32]

You're doing it again.

You are trolling again.

[jfo]

I need to do the fluid on all 3 of my diffs. The front and rear look super easy. Is there a DIY for the center diff?

I''ve not seen a DIY, but there are threads about this if you search. The trans support bracket needs to come off to reach the drain plug. One poster used a pump to suck the fluid out of the fill plug. You would likely get about 80% of the 1L this way. I would probably use this approach if I do it again. Be prepared for the high price of the centre diff gear oil. It's 75w-90 with a friction modifier added and the only source seems to be the dealer.

[Novarider]

I''ve not seen a DIY, but there are threads about this if you search. The trans support bracket needs to come off to reach the drain plug. One poster used a pump to suck the fluid out of the fill plug. You would likely get about 80% of the 1L this way. I would probably use this approach if I do it again. Be prepared for the high price of the centre diff gear oil. It's 75w-90 with a friction modifier added and the only source seems to be the dealer.

So the center uses a different oil than front/rear?

[Smac770]

So the center uses a different oil than front/rear?

Officially, or what people try and get by with?
https://nemigaparts.com/cat_spares/e...q/636u/300630/
parts 3 and 4. rear diff uses the same as the front diff; each around 1L

[Spawne32]

So the center uses a different oil than front/rear?

I believe, and don't quote me on this, the crown center diff does, if you have the torsen I think that is just a gear oil, but I don't have the part numbers. That's a good question for a dealer.

[jfo]

I believe, and don't quote me on this, the crown center diff does, if you have the torsen I think that is just a gear oil, but I don't have the part numbers. That's a good question for a dealer.

The torsen diff uses a different oil. As I noted above it's gear oil but with Sturaco friction modifier added. This is for the 8 speed. I would think the 6 speed is the same.

[Spawne32]

The torsen diff uses a different oil. As I noted above it's gear oil but with Sturaco friction modifier added. This is for the 8 speed. I would think the 6 speed is the same.

Yes, but the crown gear center differential uses clutches, I would suspect that it uses a different fluid as well. Depending on your year you will have either the torsen or crown gear center differential. Which could change the required fluid. ZF's instructions are unclear on this, they recommend SAF AG4 1016, plus friction modifier STURACO FM 1992, but there seems to be confusion as to whether it requires the friction modifier only when new or at every service. Obviously anything with a clutch pack like the crown gear quattro diff would require a friction modifier at every service in much the same way a limited slip differential would. Easy way to check seems to be what end you have on your driveshaft at the output of the transmission. Torsen appear use a CV joint end at the transmission where as the crown diff is a keyed shaft that the driveshaft inserts into.

[Spawne32]

Also the audi fluid or "axle oil" as they seem to call it is $100 for .5 liters.

[jfo]

Yes, but the crown gear center differential uses clutches, I would suspect that it uses a different fluid as well. Depending on your year you will have either the torsen or crown gear center differential. Which could change the required fluid. ZF's instructions are unclear on this, they recommend SAF AG4 1016, plus friction modifier STURACO FM 1992, but there seems to be confusion as to whether it requires the friction modifier only when new or at every service. Obviously anything with a clutch pack like the crown gear quattro diff would require a friction modifier at every service in much the same way a limited slip differential would. Easy way to check seems to be what end you have on your driveshaft at the output of the transmission. Torsen appear use a CV joint end at the transmission where as the crown diff is a keyed shaft that the driveshaft inserts into.

Which B8's have crown gear? You are probably correct about the fluid they use , but I'm only referring to the torsen. I asked ZF about the notion of not needing to use the oil with Sturaco except on a new transfer case and they would not comment on this. They would only confirm that the only approved gear oil includes the additive. I paid about $85US for 1L of dealer oil. Expensive compared to regular 75W-90 but I will probably never change it again.

[Spawne32]

Which B8's have crown gear? You are probably correct about the fluid they use , but I'm only referring to the torsen. I asked ZF about the notion of not needing to use the oil with Sturaco except on a new transfer case and they would not comment on this. They would only confirm that the only approved gear oil includes the additive. I paid about $85US for 1L of dealer oil. Expensive compared to regular 75W-90 but I will probably never change it again.

Based on what people have posted on here, there is a thread floating about id have to find it where someone looked into the differences by year, but they started switching to the crown gear diff sometime in late 2010, we started seeing that used in the B8 A4's. It seems to be that very early B8's still using the ZF 6HP28 used the torsen for about a year or two. Not sure if ALL the 8 speeds came with the crown gear, or some, there seems to be some sort of cross over year where this happened.