CHANGING VERY OLD TRANS FLUID

[Larz]

I've seen many posts about the PROs and CONs of changing transmission fluid after very high mileage with no previous maintenance. Personally, I get mine changed on a regular schedule, but many of us might not. Here is a video from Scotty Kilmer who explains the risks. He is a bit campy and is NOT a fan of any Nissan or Chrysler product, but I find watching his channel very interesting.

[Gene Ln]

I will admit I have not watched this particular video, I have seen and heard about many others, if I am not mistaken it boils down to the old fluid is holding the particulates back and fresh fluid can dislodge them and kill the trans right? I have read that extensively for old, prior to mid 90's, transmissions but that happens way less frequently in newer cars. I have a 03 M45 with 225k I bought it at 209k with no knowledge of prior trans service and after a few k miles I found the trans to act out I took it to a trans specialist and had all the old fluid removed and fresh synthetic put in, I did not have a "flush" done as no chemical cleaner was used, the car is shifting as good as new, or so I believe and has been since. Oh and the old fluid was like Tar. ok I watched it, yep as I thought.

I will also say that "flush" machine doesn't actually push the fluid anywhere, the torque converter pushes the fluid through the system including out into the cooler, either radiator or external which the machine is looped into the cooler lines. or at least the ones I am familiar with.

[steve_c]

I will also say that "flush" machine doesn't actually push the fluid anywhere, the torque converter pushes the fluid through the system including out into the cooler, either radiator or external which the machine is looped into the cooler lines. or at least the ones I am familiar with.

Good post Gene!

Just to clarify,
The torque converter does have an impeller assembly (internal pump) that directs mechanically driven fluid to the converter's turbine assembly, starting the "fluid coupling sequence", but that energy stays within the torque converter & its components.

It is the job of the transmission pump (separate component) that does the work of lubricating & moving the fluid to all parts of the transmission, including the cooler!

[Gene Ln]

I will also say that "flush" machine doesn't actually push the fluid anywhere, the torque converter pushes the fluid through the system including out into the cooler, either radiator or external which the machine is looped into the cooler lines. or at least the ones I am familiar with.

Good post Gene!

Just to clarify,
The torque converter does have an impeller assembly (internal pump) that directs mechanically driven fluid to the converter's turbine assembly, starting the "fluid coupling sequence", but that energy stays within the torque converter & its components.

It is the job of the transmission pump (separate component) that does the work of lubricating & moving the fluid to all parts of the transmission, including the cooler!

Thank you, yes I lump the torque converter and pump in the same even though they should not be, mainly because without the spinning action no pumping happens.

[MM...Good]

I will admit I have not watched this particular video, I have seen and heard about many others, if I am not mistaken it boils down to the old fluid is holding the particulates back and fresh fluid can dislodge them and kill the trans right? I have read that extensively for old, prior to mid 90's, transmissions but that happens way less frequently in newer cars. I have a 03 M45 with 225k I bought it at 209k with no knowledge of prior trans service and after a few k miles I found the trans to act out I took it to a trans specialist and had all the old fluid removed and fresh synthetic put in, I did not have a "flush" done as no chemical cleaner was used, the car is shifting as good as new, or so I believe and has been since. Oh and the old fluid was like Tar. ok I watched it, yep as I thought.

I will also say that "flush" machine doesn't actually push the fluid anywhere, the torque converter pushes the fluid through the system including out into the cooler, either radiator or external which the machine is looped into the cooler lines. or at least the ones I am familiar with.

My new to me 2007 M35X has 119K on the clock. The prior owner never changed the transmission, differential or transfer case fluids. I think I changed mine twice in 105K on my 2006. I'm planning on having it done in the next month or so. Any concerns?

Thanks.

[MWumbo]

I am in the same boat. I just picked up a beautiful 2006 M35 with 110K on the odo. I mentioned it to the dealer that I am not sure if it was ever changed. They said they would be afraid to change it. Why????

[EdBwoy]

I was once in the same boat. I bought an M45 with 190k miles. There was scant evidence of any maintenance and more evidence of neglect.

I took it to the dealership for a trans fluid replacement and I went on my way. The car did not shift any perceivably worse or any better. I just enjoyed the peace of mind and comfort in knowing good fluid is almost always better than used/broken down fluid.

This is purely anecdotal, so take it as you please.

[steve_c]

Transmissions use clutch packs to engage & disengage the various speeds that are called for.
The more speeds you have in a transmission, the more clutch packs required.
The clutches are made up of a friction material like brake pads are.
If you do a lot of low speed urban driving, you are using your 1st & 2nd speed clutches more than the higher speed clutches.
Transmission fluid is engineered to be compatible with the clutches, insuring minimal wear & tear to the clutch friction material, protection from heat, etc.

Over time, transmission fluid breaks down, so its ability to protect these clutches are marginalized as heat & usage from normal & severe operations continue.

The clutches now begin to wear faster as the protective quality of the lube diminishes.
this starts a vicious cycle: as the friction material wears off of its backing plate, the friction material raises the viscosity (thickness) of the oil, (the particles become suspended in the oil) slowing it down as it travels through the valve body ports & the valves themselves.
This slowdown causes the clutches to engage & release more slowly, and increases operating temps of the transmission as the oil cannot flow as smoothly & quickly due to the buildup of friction material now suspended in the oil. This now dirty oil cannot dissipate the heat as quickly, increasing clutch material wear.
Adding to this is the transmission filter, if equipped. This too is clogging up with friction material, making the pump work harder & hotter.

As the miles & usage pile on, the clutch wear continues to a point where the clutches are thin & burnished, hard & brittle.
At this point, the only thing that keeps it all together is the friction material in the dirty oil, it actually makes the clutches continue to do their job by depositing the friction material back between the clutches.
Problem is, this material belongs on the clutches, not between them suspended in the oil!

At this stage your transmission could already be toast, or on borrowed time. If you start to feel it misbehaving & decide a fluid change is in order, you may be too late.

The new fluid you put in now is as good as new, but if your clutch packs are shot, as described above, the new fluid cannot restore the clutch material you already lost.
Without the friction material, the burnt, hardened, or just worn out clutches are now just slipping with the new fluid!

[steve_c]

I was once in the same boat. I bought an M45 with 190k miles. There was scant evidence of any maintenance and more evidence of neglect.

I took it to the dealership for a trans fluid replacement and I went on my way. The car did not shift any perceivably worse or any better. I just enjoyed the peace of mind and comfort in knowing good fluid is almost always better than used/broken down fluid.

This is purely anecdotal, so take it as you please.

So here is the rub:
What to do?
As you can see, for every bad story you hear, a good one is lurking around somewhere!
The takeaway is: YMMV!

What can you do to make a better informed decision?

You could go to Blackstone (or equivalent) and get a trans fluid test kit.
Fill the bottle with a sample of your fluid & get it tested.
They will send you back an analysis report that might help you decide whether it would be worth it or not to do a fluid change if you are undecided!

[steve_c]

I am in the same boat. I just picked up a beautiful 2006 M35 with 110K on the odo. I mentioned it to the dealer that I am not sure if it was ever changed. They said they would be afraid to change it. Why????

MWumbo,
I answered your question in an above post by explaining the normal wear & tear on transmission clutch packs.
All being said, many dealers (and Indys) are afraid to change fluid after a certain mileage because if the unit begins to slip, they may be blamed for the problem.
Transmissions do not last forever, like all components they have a service life. Changing the fluid can prolong the service life. The argument is at what mileage does changing original fill oil bring back minimal returns!
Todays oils and clutches are better then they have been in the past, so at what point is it safe to change out original oil?
50 to 100k miles? 100 to 200K miles?
This appears to be the argument generating so many opinions!

[MWumbo]

It's true and I appreciate the great responses. I don't think I will deal with the dealer. There are a couple of "Z"shops that specialize in Nissan and Infiniti cars near me. I will chat with them and get their opinion on the subject too. I will let you all know what they say. Although I didn't start this thread, I appreciate the honesty!

[EdBwoy]

Good explanation Steve.

There have been other debates on this, and sure enough it depends on your level of comfort... and YMMV.
In general I go by these principles: if you're doing it to be proactive, good idea. If you are fumbling to replace your fluid because your transmission is already slipping, it's like the people who do an expensive synthetic oil change after the engine starts knocking. The chances of success are slimmer.

Surprisingly, a transmission fluid service is the one thing I go to the dealer for. In my area, we don't have many specialty independent shops. You get the correct fluid and the charges are strangely palatable for this service at both Infiniti and Nissan.