MTF and diff oil change interval for me

[dparm]

Any suggestions for a change interval for my MTF and/or rear differential fluid?

MTF is also the center diff so it uses almost 4 qt of GL-4 75w90. Audi says it has a 50k change interval. The rear diff is about 2 qt of GL-5 75w90 and is "lifetime".

My car is driven pretty hard. It sees 10-12 autocrosses during the spring & summer, and maybe 2 or 3 track days. I also run it up to redline pretty often on on-ramps or whatever. But I do not put many miles on the car each year, under 7500. It's not much of a DD since I use public transportation.

Right now I do the change once a year once race season ends (early to mid autumn) so that whatever metal or other garbage doesn't linger. Right now I have Motul Gear 300 in each. Might find something a bit lighter to improve winter shifting...still undecided.

 

[tomcat27]

The most important change is the very first change - as it removes break-in wear particles. (verified by extensive testing by Amsoil) Hmmm.... There is certainly nothing wrong with your annual change - you could likely stretch that to 2 or 3 years. But if you wanna be certain....

 

[dparm]

I changed it right around 50k when I got the car, ironically. Since then I've changed it one other time, which was about 58k (last autumn). Both times it got Gear 300.

OEM MTF is actually Castrol TAF-X which is a very stout formula, so I'm sure it was fine for the first 50k.

 

[Steve S]

Originally Posted By: tomcat27
The most important change is the very first change - as it removes break-in wear particles. (verified by extensive testing by Amsoil) Hmmm.... There is certainly nothing wrong with your annual change - you could likely stretch that to 2 or 3 years. But if you wanna be certain....
The first oil change to flushout debris is as old as the sun. There have been SAE studies on the subject, I used to read the trade magazines at work.

 

[mechtech2]

I am a too frequent lube changer.

At once a year with your rate of miles accumulated, you are certainly in contention to be one also!

If you can eat the costs with no regurgitation, then of course it's always best to have fresh fluid in there.
But every 2-3 years would be more like it for you.

 

[dailydriver]

Originally Posted By: mechtech2
I am a too frequent lube changer.

At once a year with your rate of miles accumulated, you are certainly in contention to be one also!

If you can eat the costs with no regurgitation, then of course it's always best to have fresh fluid in there.
But every 2-3 years would be more like it for you.


I've got you both beat when it comes to the OCD lube changing; twice a year on the gearbox, and at least 3 times a year on the over-stressed rear axle/diff!!

YES, extremely wasteful, I know (but I can't help it!).

 

[dbrowne1]

I have yet to see anything beyond pure theory and speculation to indicate that Audi's claim of "lifetime fill" for its manual transmissions is wrong. Are there any analyses out there of fluid from VW/Audi manual transmissions showing that the fluid is no longer usable after X miles or years?

I have 115K miles on a modified 1.8T A4 and it shifts as smooth as it did at 50K miles.

I had a 1.8T VW years ago that had even more mods. I changed the MTF at about 90K miles and, at least visually, it looked perfectly fine. Slightly darker than the new OEM fluid that replaced it, but comparable viscosity and absolutely nothing that resembled metallic or insoluble particles. I did not have it analyzed, but that was partly because my reaction when it drained out and I looked at it was "gee, why did I bother changing this."

 

[mechtech2]

Lifetime fluid is like perpetual motion.

Either will work for a while. But inevitable deterioration occurs.

 

[dbrowne1]

Originally Posted By: mechtech2
Lifetime fluid is like perpetual motion.

Either will work for a while. But inevitable deterioration occurs.


There has to be at least some amount of mechanical degradation/shearing and some accumulation of wear metals, but these are sealed gearboxes that don't have combustion byproducts and such. As we know from "Oil 101," it's the additives, not the base oil, that gets depleted - and there's not much way to deplete sealed MTF chemically.

So I'm still not seeing how a high quality synthetic MTF in a sealed gearbox (which is what we have in the VW/Audi cars) gets depleted before the rest of the car falls apart.

 

[[RT] ProjUltraZ]

even w/ the track duty, i would cut the manufac recommd by over 60% and still only change every 2 years. like every 15,000

 

[rpn453]

Originally Posted By: dbrowne1
There has to be at least some amount of mechanical degradation/shearing and some accumulation of wear metals, but these are sealed gearboxes that don't have combustion byproducts and such. As we know from "Oil 101," it's the additives, not the base oil, that gets depleted - and there's not much way to deplete sealed MTF chemically.

So I'm still not seeing how a high quality synthetic MTF in a sealed gearbox (which is what we have in the VW/Audi cars) gets depleted before the rest of the car falls apart.


Since there's no filter, it's the wear particles that I'm concerned about when I change gear oil. That's why I like to do a change shortly after break-in. After that, 60k mile intervals are enough to satisfy me. I would do it more often for a car seeing track use though.

 

[dbrowne1]

Originally Posted By: rpn453
Originally Posted By: dbrowne1
There has to be at least some amount of mechanical degradation/shearing and some accumulation of wear metals, but these are sealed gearboxes that don't have combustion byproducts and such. As we know from "Oil 101," it's the additives, not the base oil, that gets depleted - and there's not much way to deplete sealed MTF chemically.

So I'm still not seeing how a high quality synthetic MTF in a sealed gearbox (which is what we have in the VW/Audi cars) gets depleted before the rest of the car falls apart.


Since there's no filter, it's the wear particles that I'm concerned about when I change gear oil. That's why I like to do a change shortly after break-in. After that, 60k mile intervals are enough to satisfy me. I would do it more often for a car seeing track use though.


OK - some honest questions here:

1. What is wearing and - more importantly - what harm are the wear metals causing? I drained the factory fill from a VW manual transmission at 90K and there were no visible particles in it, and a slightly darker color. I'm sure there were millions of tiny wear particles in there from the synchros, but what is that going to damage?

2. How do arrive at a 60K interval?

Again, there just seems to be a lot of internet speculation on this topic and not a lot of empirical evidence to refute the factory's "lifetime" claim. VW/Audi has had some bogus recommendations before on fluids and intervals, like the 10K changes on transverse 1.8T engines, but all of that has been shown with real evidence of sludging and UOAs to be a poor interval.

 

[rpn453]

Originally Posted By: dbrowne1
OK - some honest questions here:

1. What is wearing and - more importantly - what harm are the wear metals causing? I drained the factory fill from a VW manual transmission at 90K and there were no visible particles in it, and a slightly darker color. I'm sure there were millions of tiny wear particles in there from the synchros, but what is that going to damage?

2. How do arrive at a 60K interval?

Again, there just seems to be a lot of internet speculation on this topic and not a lot of empirical evidence to refute the factory's "lifetime" claim. VW/Audi has had some bogus recommendations before on fluids and intervals, like the 10K changes on transverse 1.8T engines, but all of that has been shown with real evidence of sludging and UOAs to be a poor interval.


Gears, bearings, and synchros are wearing, putting abrasive particles into the oil. They would have to be thicker than the oil film to actually increase wear, so it may be a non-issue in many cases, especially once the biggest break-in particles are removed. But you wouldn't be able to see particles as small as the thickness of the oil film between gears under pressure. If you could see anything, then those would be really bad ones!

60k is simply a typical interval in applications where the manufacturer specifies one. If they don't, they are probably sacrificing some longevity for convenience, saving valuable time for the wealthy North American consumer. They're probably doing the right thing, as the original owner is unlikely to keep the vehicle until mechanical failure anyway. In the rust belt, it's pretty much a certainty that the car will be worthless by the time transmission or gear oil degrades enough to contribute to component failure. I have no other way to explain why Mazda thinks I never need to change my MTF unless I'm outside of North America, where they think I should do it every 60k. Strangely, they also think I should change my brake fluid occasionally if I'm not in North America. It's another "lifetime fill" item here.

It's good that you're wanting solid information to base your decisions on. Unfortunately, I have none to offer. The general information is out there somewhere, but it would be difficult to find anything good about specific applications. I don't need to research it because I know that I do more than enough to keep my major mechanical components in good condition based on common practices. So I'm content, and that's what it's all about. If I didn't enjoy getting new fluid in there, if it was difficult to do, or if I had to pay someone to do it, I'd probably look at stretching it out as long as possible.

The only thing I can say for sure is that 90k miles is way too long to leave the original MTF in a '98 Pathfinder. That stuff came out black and nasty, and it shifted much better with some new fluid.