BMW tried that in the final drive of some of their bikes and went so far as to not include a fill hole in the housing. Doanno if they still do.

Lifetime fill in our 2004 BMW 325. Reverse and drive started delaying when selected. At 90k.

Bought a kit based on what type of trans (GM made trans for some!) and it came with proper fluid, filter, gasket and all new bolts. All delay gone, shifted like new. Was a little worried, believed the hype "Only BMW can service the trans. They refused to change the fluid, so no options.

Filled per instructions, car is now 170k, maybe time for another change. Still shifts like new.

Had a similar situation with my BMW 525i with 128K. Spoke to a very reliable and experienced transmission mechanic who services BMW, Mercedes, Volvo, etc. His advice was as mentioned by a few in this thread. Basically, if the fluid is changed regularly at, say, 50-60K, there should be no problems. Once you get around 100K on the "lifetime" fluids, changing should be done with only partial fluid replacement. New fluid has much stronger "cleaning" chemicals that older fluid and to introduce that to a well used system often results in failures within the near future.

Well yes and no. I have seen multiple examples of gearboxes never being drained and when properly sealed they last a very long time. There are several ways to get metal of the gear and into the oil:
Abrasive Wear: from particulate that plows, gouges, cuts the surface. This typically happens upon start-up when the metal surfaces of the gears are touching with minimal oil film to separate them. Only under full operation is there a complete separation so there is a very minimal opportunity for that sort of wear to occur.

External contamination is typically to blame. If you looked under a scope you would see what look like nail clippings. Sometimes there is also rubbing wear which is considered normal wear and that occurs with new components - some call it break-in wear. Those look like platelets. None of these you can see with the bare eye.

Surface Fatigue: from very hard particulate that is forced between the two surfaces and due to such high localized pressure will actually contribute to a crack or fissure on the surface. This is referred to as spalling. The crack will propagate and the surface becomes compromised. Particles are typically spherical in shape. You can also get pitting from particles as well as Brinelling which is due to a dis-harmonic producing atypical vibrations. I some cases (but not in diffs or trans) you can get hydrogen embritterment. Again, not that common in over the road applications but worthy of mention. Surface fatigue is typically due to external contamination (sand) but it can happen with wear particles due to surface contact.

Adhesive Wear: from the two surfaces coming in contact under really high load without the oil film. In such cases even the anti-wear or extreme pressure agents in the oil can't help much. In this scenario you will have scuffing, galling, and even seizing of the gear faces. If the force is ridiculously large the gear teeth will cold well and the set is seized. Its rare but I have seen it. Normally the force is greater then the weld point and chunks of metal break off and tumble around creating havoc and despair. If you have a compromise of the oil film you can get adhesive wear and the particles have a particular shape. This is considered severe sliding wear and they have a plate shape.

There is also chemical wear (fretting, corrosion, static corrosion, rust) but if you have a closed system that would not normally happen. It is possible to get cavitation corrosion which is an implosion of micro air pockets. This is due to pressure differences but the likelihood of that happening on a trans or a diff is remote. Maybe micro-dieseling but even then, the formula of the oil has a stout amount of anti-foam so its rare - could happen if there is water but again, a closed system wouldn't allow it.

Now why is it good to know all these failure modes? Because if you know why it fails maybe you can work towards prevention and that is exactly what I have been doing with several large OEMs that make heavy equipment including engines and what have you. I have helped several of these start a wear debris library. Pulling oil samples form lots of different stages and various models under various conditions goes a long way in designing in maintainability. I also work with several major oil companies as well as several independents doing the same but also looking at used oil condition and chemistry. Now why would an oil company want to develop an oil that would stay in the box forever? Because they all know that if that is not the goal then their competition will achieve it.

I have seen diesel engine oil formulas achieve >100,000 miles between changes - this is from a few different angles, from the oil formulas and the OEM (tolerances, metallurgy, designs) and filtration. I always thought that if an oil company built engines or an engine company formulated oil it would happen faster. To be that vertically integrated is really tough. They do have some great partnerships out there which is very encouraging.

So, how do you really know when to change your oil? You have to test it. No other way.

Yeah, testing it will tell you when to change the oil, after you already changed it.

Cheaper and easier as an end user to just change the fluids on time, like I have been doing the last 30 years.

You can pull a sample without draining.

https://www.youtube.com/watch?v=IrMzQ9sQoE4&t=1s

and if you wish to see a commercial lab in action...

https://www.youtube.com/watch?v=ac0-sOZBReM&t=68s

In cases such as my M3's trans or diff, the amount of effort to pull a sample to test is, for all intensive porpoises, the same as to just change it.

Yes! The perfect reason to have a lube for life! But in order to get there requires data, data, and more data. That means sampling, testing, analyzing, diagnosing...and sampling some more.

No, that is not a perfect reason to have lifetime lubricants.
That is the case with every single car I have ever had. If I am getting a sample, I am replacing the fluid, period.

I change my stuff often enough doing oil analysis never really occurred to me.

Lifetime lube is a self fulfilling prophecy.

Thank you.

Why does this have to be so complex.

Well, on our beater Saturn we have 160k/21 years on the same tranny oil....I'll never change it...it is a beater...but runs really well and shifts smoothly....so, for me, it is a lifetime fluid :).

They are great bumper cars too (wife is a PharmD) and it lives in a parking lot and gets hit all of the time...the plastic panels just pop back out...how do we know when it has been hit....a 20 dollar bill under the wiper (like that is a fair deal aye lol)...so far we are over 300 bucks.

Seriously? That is righteous that folks would assess damage that meticulously.

Hey.... My x-girlfriend was a pharm-d and drove a saturn!!!!
Your Saturn isn't dark blue is it?

Isn't the goal of this forum for people to enable/encourage other like minded people to embark on missions of futility with unnecessary and needlessly overengineered stuff? The saturn does not qualify!!!!


I appreciate MD's thorough write-up. I used to test my used brad penn to see how the 911 was doing after changing the oil. It always came back good. It was nice to know. I can geek out for hours on that type of stuff. OTOH- while that info might be good for long term improvements/ benefit in industry/ fleet vehicles, or humanity at large, to me it is largely academic.

I can test my oil to see if it is okay. Perhaps it is. If I test it a year later, and it is not, then for a period of time damage was occurring, and the transmission was taking somewhat of a beating. At some time- the oil will become contaminated. To a certain extent, the transmission would be the sacrifical lamb.

I was in a local shop recently looking at a volvo transmission the owner had courageously tried to rebuild himself (unsuccessfully). It was more complex than C3PO. In the middle was an unserviceable oil filter that was 2/3'rds clogged with crap.


If I change the oil preventatively, especially if the oil was still good, the oil itself is the sacrificial lamb- which is better than the transmission itself.

The oil change itself is always stressful- the prospect of introducing contaminants, loosening debri, incorrect refilling, etc...., but it's done.

Now I'm on to stress out about other stuff! :D

I know, not kidding either....the first time Mary found a 20 she was...'What's this all about'...'Honey, someone hit your car'
On the Saturn the plastic body work will dent...then, given time pop back out...and the color is impregnated so no issues with the paint....
For a 'cheap' vehicle in '97 it has never failed to 'go'....I had to replace the radiator and honestly...100 bucks and an hour job. Everything just works and...and, no rubber cam belt...it has an oil bath chain for God's sake.
The best beater car you can buy....

You're right tho.....given their perspective what does a 20 buy you at the body shop....never and address/name...just a 20....rat bastards lol....

A 20 buys you half of a front suspension rebuild.

Nothing is over $100 on a Saturn if back yard fixin'.

Love those plastic bee-otches.

Glad for this discussion. I have a 2013 Mazda 5 that showed dirty transmission fluid at 60K. I was 750 past the warranty when I asked them to look at it. I pulled the pan, changed the filter and replaced the fallen fluid. I think I once again drained and filled. I probably replaced....50-60% of the fluid. It is still not RED, and looks mostly gray.

I would happily (a relative term) have the dealer flush and replace 100% if I thought it would do more good than harm. There is no slippage. I suspect the torque converter, not so much the transmission, based on a little vibration mostly, developed lately. All its life, building torque after a stop has required a little more RPMs than most transmissions, but the car has always otherwise shifted just fine. I think this needs a different torque converter, but my first decision is whether to replace the fluid or not. More harm than good? More good than harm?

Your perspective appreciated.

Lubey, I'm curious about your last comment...more bad than good. I've heard the stories about sudden trans failure following fluid change and have always written them off as coincidence.

Why?

Bump. You guys have failed to answer my question. SmileWavy The car has 90K miles. No slipping or shifting problems. Suspect torque converter. I am thinking about having the fluid flushed/replaced. I predict this would do more good than harm, but not sure about that.

greglepore has a similar question. We know that dirty fluid can contain abrasives that the tired/worn transmission now needs, and that flushing and replacing that fluid can cause the transmission to have a slipping problem.

Chemistry. It is really about the chemistry. And although oil companies say they produce products that are 'backward compatible' it doesn't mean they actually work better. Formulas change almost annually. That said, the countless hours spent in R&D along with road work to find the right recipe will be changed within a year. Now some will say that the product is the same, of better. The thing is, your Grandmothers toll house cookies or the McDonalds fries of the 70's were better then your Wife's gluten-free, fat free, taste free 'cookies' or the new MickyDs fries sans trans fat which are supposed to be better right? Hmmmmm. Combine that with introducing contaminates (less then 20 micron particles create the most wear - that is not much bigger than a white blood cell) and its a recipe for failure.