CVT fluid change

I'm not wanting to discuss whether a fluid change should be done on the CVT or not, because that has been done to death already. My question is specifically related to the benefits (if any) of doing a fluid change (as against a "flush") if the result is only plus or minus 50% (or less) of the "old" fluid is removed and replaced by the "new."

I know some of the replies might be that the procedure could be repeated several times to achieve a higher "fluid changeover" figure, but I'm not sure that the high cost of the CVT fluid would justify the multiple changes. Maybe for the DIYer's on the forum then that would lower the financial burden, but for the average joe (me included) who goes to the dealer for most services, I don't really see the value in a fluid change if, as some reports I have read, as little as 1/3rd of the fluid is all that is replaced.

I am an admitted skeptic of the "never needs changing" mantra, but I'm not convinced that a "relatively small" addition of "new fluid" is going to make a heap of difference to the health of my CVT. I welcome other opinions.

Personally I think that the fluid should be changed around 60000 km (40k miles) to 100000 km (60k miles) depending on driving conditions and how the fluid looks like.

One way to do it would be to actually disconnect the lines to the oil cooler and let the oil drain into a container while refilling at the same rate as it's draining until the color achieves the same as the new fluid. This would be with the engine idling and shifter in neutral. A bit tricky, but doable and it would replace most oil in the system that way in one operation.

Regardless of way you do it the fluid replacement will cost some money. But would still not be as bad as a new gearbox.

I also found this: https://www.twincitysubaru.com/service/maintenance-schedule.htm

There the CVT flush is listed at US$309.95 plus tax. Should be similar regardless of where in the world you are.

And of course - the differentials should also see an oil change at those distances.

I also found this: https://www.twincitysubaru.com/service/maintenance-schedule.htm

There the CVT flush is listed at US$309.95 plus tax. Should be similar regardless of where in the world you are.

Interesting that the dealer you referenced recommends a flush. My dealer is one of those believers that preach that the CVT is a sealed unit and doesn't need maintenance ( other than the scheduled inspections.)

I did a little bit of Googling and came up with this supposedly "transmission expert" who states ......

"For a manual or CVT transmission a basic drain and fill is all that is required"

https://www.thompsonimportrepair.com/transmission-fluid-flushes/

So it looks like there might be not only disagreement about whether the CVT fluid should be changed at all, but also as to whether a drain and fill or a flush, is the way to go

I am an admitted skeptic of the "never needs changing" mantra, but I'm not convinced that a "relatively small" addition of "new fluid" is going to make a heap of difference to the health of my CVT. I welcome other opinions.

You only need to look at other brands with 'lifetime' fluids to understand how spectacularly they fail when they go over 100k.

There's also the issue of not being able actually check the fluid ... when our A6 started leaking out the prop shaft seal @ 80k, we had no clue how fast it was leaking or how much was left because there was no way to check the fluid without lifting the car and removing the fill plug. There was no drain plug ... the entire pan had to come off, to measure the amount of fluid left. If it were a slow leak we wouldn't bother fixing it, but since we had no clue we had to drop the unit and replace the seal.

Interesting that the dealer you referenced recommends a flush. My dealer is one of those believers that preach that the CVT is a sealed unit and doesn't need maintenance ( other than the scheduled inspections.)

I asked my SA when we bought it. He said "yup, change the fluid, but we have no guidance from SOA how frequently, so let's consider 60k". He also said it's not really a DIY operation because they need some computer tool to cycle the internal pumps and get it all out.

most automatics typically do first change at 60K and then every 30K afterwards for drain and fill. I have followed the drain and fill every 30K on my 03 Subaru and it runs just fine with 130K on it. next drain and fill will be in the spring and that is when I will drop the pan and change the filter as well. I changed the spin off filter back at 90K. My 2014 will not see a CVT fluid drain until 100K as the trans was replaced at 40K. I do mostly short trips (10 miles each way) with occasional long trips (800 miles each way)

Car reports that after 16K miles on new trans, CVT fluid degradation is 1.7%

to do it yourself, watch the above video

I have followed the drain and fill every 30K on my 03 Subaru and it runs just fine with 130K on it. next drain and fill will be in the spring and that is when I will drop the pan and change the filter as well. /QUOTE]

 

Thanks for that. I assume from your informative reply that you are happy with the amount of new fluid that is delivered by the drain and fill method .... because that was the main point of my original post. I'd basically like to know at what point (if any) is it a waste of time draining and filling. For example, if the drain and fill method replaces 100% of the fluid (which I know it doesn't) then you have a perfect result. 75% percentage replacemnet would still be great (but again not going to happen in the real world) .... I assume 50 % would still be a good result ...... what about 35% or 25% (or maybe less) ...... so is there a cut off point where you would say it's not worth it .... or do you subscribe to the theory that it can't hurt and any introduced new fluid is a help.

 

Also in your reply you mentioned dropping the pan. Can you elaborate on that. How much more fluid is drained by doing that extra step.

One reason for dropping the pan is to clean it from sludge that don't come out when you drain the pan. That sludge is sometimes like tar.

On some vehicles there are also magnets inside the pan that collects metal particles, but that may vary depending on manufacturer.

One reason for dropping the pan is to clean it from sludge that don't come out when you drain the pan. That sludge is sometimes like tar.

The Subaru CVTs shouldn't generate nearly as much sludge as conventional automatic transmissions do, since the the only time the forward and reverse clutches engage/disengage is while the vehicle is stationary (or moving very slowly) as you select Reverse or Drive.

I have followed the drain and fill every 30K on my 03 Subaru and it runs just fine with 130K on it. next drain and fill will be in the spring and that is when I will drop the pan and change the filter as well.

 

Thanks for that. I assume from your informative reply that you are happy with the amount of new fluid that is delivered by the drain and fill method .... because that was the main point of my original post. I'd basically like to know at what point (if any) is it a waste of time draining and filling. For example, if the drain and fill method replaces 100% of the fluid (which I know it doesn't) then you have a perfect result. 75% percentage replacemnet would still be great (but again not going to happen in the real world) .... I assume 50 % would still be a good result ...... what about 35% or 25% (or maybe less) ...... so is there a cut off point where you would say it's not worth it .... or do you subscribe to the theory that it can't hurt and any introduced new fluid is a help.

 

Also in your reply you mentioned dropping the pan. Can you elaborate on that. How much more fluid is drained by doing that extra step.

I will not drop the pan on the '14 CVT, I will drop it on the 03 since it will by that time need a filter change, which is only accusable by removing the pan.

I'm still kinda hanging out for an answer to my basic question, so I'll try asking once more before I stop boring y'all I'd basically like to know at what point (if any) is it a waste of time draining and filling. For example, if the drain and fill method replaces 100% of the fluid (which I know it doesn't) then you have a perfect result. 75% percentage replacemnet would still be great (but again not going to happen in the real world) .... I assume 50 % would still be a good result ...... what about 35% or 25% (or maybe less) ...... so is there a cut off point where you would say it's not worth it .... or do you all subscribe to the theory that it can't hurt and any introduced new fluid is a help.

Also how much more fluid is drained by dropping the pan.

The Subaru CVTs shouldn't generate sludge like conventional automatic transmissions do, since the the only time the forward and reverse clutches engage/disengage is while the vehicle is stationary (or moving very slowly) as you select Reverse or Drive.

I have found sludge in manual gearboxes, so I'd be surprised if there isn't any.

I'm still kinda hanging out for an answer to my basic question, so I'll try asking once more before I stop boring y'all I'd basically like to know at what point (if any) is it a waste of time draining and filling. For example, if the drain and fill method replaces 100% of the fluid (which I know it doesn't) then you have a perfect result. 75% percentage replacemnet would still be great (but again not going to happen in the real world) .... I assume 50 % would still be a good result ...... what about 35% or 25% (or maybe less) ...... so is there a cut off point where you would say it's not worth it .... or do you all subscribe to the theory that it can't hurt and any introduced new fluid is a help.

 

Also how much more fluid is drained by dropping the pan.

you might get a third of the fluid... with a drain and fill. I have seen dudes on YT use the internal pump to change out the fluid on a CVT...but when you are done you will need to make sure it is at the right level by removing the fill plug when it is up to operating temp (Subaru has a procedure for that)

removing the pan does not get but a tiny amount more that is in the pan... on a CVT you do not need to remove the pan...

you might get a third of the fluid... with a drain and fill. I have seen dudes on YT use the internal pump to change out the fluid on a CVT...but when you are done you will need to make sure it is at the right level by removing the fill plug when it is up to operating temp (Subaru has a procedure for that) removing the pan does not get but a tiny amount more that is in the pan... on a CVT you do not need to remove the pan...

Thanks for that

Personally I think that the fluid should be changed around 60000 km (40k miles) to 100000 km (60k miles) depending on driving conditions and how the fluid looks like.One way to do it would be to actually disconnect the lines to the oil cooler and let the oil drain into a container while refilling at the same rate as it's draining until the color achieves the same as the new fluid. This would be with the engine idling and shifter in neutral. A bit tricky, but doable and it would replace most oil in the system that way in one operation.

 

Regardless of way you do it the fluid replacement will cost some money. But would still not be as bad as a new gearbox.

I came across this article today. I guess there might be some complaints that it isn't CVT or even subaru specific, but I think it contains some useful "general" info on transmission fluids ... and that it has at the very least, some relevance to all transmissions ... (if not, then it can be removed )

https://axleaddict.com/auto-repair/Automatic-Transmission-Fluid-Change-Interval

Since you are open to opinions, here is my view:

I agree that a drain and fill will only have a certain effect as it will only get out a limited amount of fluid. That being said, any bit should theoretically help, assuming the fluid is actually bad. The idea of a lifetime fluid isn't totally new. My 09' Corolla also has lifetime transmission fluid which has yet to be changed at 125k miles. My theory is that newer transmissions are much less susceptible to exposing transmission fluid to moisture, which is a primary source of fluid degradation. These studies looked at the effects of moisture on ATF, although not specifically Subaru's. A simplified summary of their findings says that there is insignificant fluid degradation in an uncontaminated (dry) sample.

Another major factor of degradation is the temperature of the oil; however, this "should be" easier to control as the system can be designed to have sufficient cooling under expected operating conditions. So if the fluid doesn't degrade significantly under normal operating conditions, there would be no point in changing it - which is how I believe Subaru came up with their recommendation. They also recommend changing the fluid under severe conditions which they exclusively list as repeated trailer towing at 40k km. Since the manual clearly states the legacy is not intended for towing, they can get away with saying the fluid will last the lifetime of the car.

So, if you use your car to get to point A to point B and you never have your ATF Temp warning light turn on, I personally wouldn't bother doing anything with your fluid.

If you drive somewhere in between that of normal and towing (maybe mountain area, or you live in a very hot climate), then maybe do a drain and fill at some point. Even this is probably more just for piece of mind in practicality than actual need.

And if you tow often against Subaru's recommendation. Change it based on their severe schedule.

In my case, I personally like the CVT fluid degradation % reading you can get from an OBD2 reader and certain apps. I'm at ~44,000 miles and 3.2% fluid degradation. Based on my own arbitrary change interval, I will probably change out my fluid around 25% degradation. That will put me at around 350,000 miles. Based on around 15,000 miles a year, that will put my car around 23 years old - so no I probably won't be changing my fluid as my car will have probably reached its "lifetime" well before that. I would be ecstatic if my car hasn't completely rust out by that point!

If you ever meet a Subaru engineer who personally works on specifying which fluid they put in their CVT that says to change it, then take his/her advise over mine or anyone else's on this forum!

My theory is that newer transmissions are much less susceptible to exposing transmission fluid to moisture, which is a primary source of fluid degradation.

The Subaru CVTs still have a vent to ambient air, which provides a path for water vapor to enter. I think high-temperature oxidation, mechanical shearing, and particulate contamination are more important determinants of CVT fluid life than exposure to moisture in the air may be. This conjecture is bolstered by the facts that 1) Outbacks have a secondary CVT fluid cooler not present in Legacys, presumably to accommodate towing, and 2) "repeated trailer towing" is the only "severe driving condition" that invokes periodic CVT fluid replacement.

I would say that when the ATF light (or corresponding for CVT) comes on you are long overdue for a replacement of the fluid.

There is no such warning light in Gen 6 Legacys or Gen 5 Outbacks , just a "CVT fluid overtemp" light. Get that very often and it's probably time to change fluid. There may be a "fluid life used/remaining" variable maintained in the TCM (CVT controller) that seems to be based on time and temperature..

It's ... particles from wear that the fluid has to absorb. Some of these particles are small enough to pass through filters but will still cause unnecessary wear.

I would say that when the ATF light (or corresponding for CVT) comes on you are long overdue for a replacement of the fluid. It's not just humidity but also particles from wear that the fluid has to absorb. Some of these particles are small enough to pass through filters but will still cause unnecessary wear.

Here are some of the particles that I assume you are referring to.

P.S. The guy in the video obviously hasn't read the manual in regards to the CVT being a "sealed unit"

due to the design of the Subaru CVTs they throw far less debris into the fluid. The torque converter lockup clutch is probably the biggest source of clutch wear particles in these CVTs. There are actually two filters in the TR580: 1) a sump-mounted "strainer" like the filter in a conventional automatic transmission, and 2) a presumably much finer cartridge-type filter that can only be replaced by disassembling the CVT.

I readily admit that I am not a "technical" person, and that I take my vehicle to the dealership for all servicing. But what I do try and do is get a basic understanding of how the car operates, and to also get a basic understanding of what the dealership is doing (or should be doing.)

With that in mind, I was wondering if the more technically inclined forum members would have an opinion on the following website. I'd like to know if the general feeling was if or not I could take what they are saying overall, as "facts" or not. And as a specific example, I am particularly intererested in their 8 stage Drain and Fill instructions for the CVT. If forum "techno experts" consider these instructions are "legit", then I would use these instructions as a basis for discussions, if and when I am deciding on who to trust for my transmission fluid change.

Any comments would be appreciated.

https://atracom.blob.core.windows.net/webinars/import/subaru_lineartronic_cvt_introduction.pdf

I had thought I would change mine, drain and fill not flush, at about 50 K miles. But in October I received a letter from SOA stating that the normal New Car Powertrain Limited Warranty had been extended to cover the CVT for 10 years or 100K miles. If Subaru has that much confidence in the CVT I think I will just leave the fluid alone. The letter said the warranty extension applied to all 2018 Legacy/Outback, Impreza, WRX, Crosstrek, and Forester. Older vehicles may be covered to some extent as well, see article below.

https://www.forbes.com/sites/jensen/2017/07/07/facing-complaints-subaru-offers-extended-warranties-on-1-5-million-vehicles/#39652d4a79dc

I had thought I would change mine, drain and fill not flush, at about 50 K miles. But in October I received a letter from SOA stating that the normal New Car Powertrain Limited Warranty had been extended to cover the CVT for 10 years or 100K miles. If Subaru has that much confidence in the CVT I think I will just leave the fluid alone. The letter said the warranty extension applied to all 2018 Legacy/Outback, Impreza, WRX, Crosstrek, and Forester. Older vehicles may be covered to some extent as well, see article below.

 

https://www.forbes.com/sites/jensen/2017/07/07/facing-complaints-subaru-offers-extended-warranties-on-1-5-million-vehicles/#39652d4a79dc

That's not how I would interpret it.

The main deficiency from Subaru is a lack of any maintenance guidelines, or even repair procedures short of complete CVT replacement.

That's the main reason I'm not going to own our CVT Legacy outside of warranty, and why I have no incentive to perform any service on the CVT.

Here are some of the particles that I assume you are referring to.

 

 

P.S. The guy in the video obviously hasn't read the manual in regards to the CVT being a "sealed unit"

Interesting video. Now as I see it wear occurs even when the load is moderate, so I'd expect some of that sludge regardless of how the car has been driven.

The main deficiency from Subaru is a lack of any maintenance guidelines, or even repair procedures short of complete CVT replacement.

That's the main reason I'm not going to own our CVT Legacy outside of warranty, and why I have no incentive to perform any service on the CVT.

Saw this today ... I guess it's merely confirmation for the "change the fluid" fraternity" (which I am a paid up member of ) and merely yadda yadda to the "lifetime" followers.

Saw this today ... I guess it's merely confirmation for the "change the fluid" fraternity" (which I am a paid up member of ) and merely yadda yadda to the "lifetime" followers.

 

I don't have a dog in this fight any more, but I am interested in knowing why Subaru Japan, Canada and the US provide different guidelines. I wonder if Japan's recommendations come from shorter drives? Or Canada's recommendations are due to colder temperatures? And in that vein, SoA had to make a blanket statement for the US, where there's both city and country driving, and temperature extremes, that covered the bulk of typical usage? Maybe there isn't a technical/rational decision for it (i.e. political or financial),

My current vehicle has a ZF8 transmission which isn't without it's own controversy. It's used by 10+ major manufacturers which (to my knowledge) claim it has "lifetime" fluid, yet ZF suggests 80-100k OCI's. Go figure.

I don't have a dog in this fight any more, but I am interested in knowing why Subaru Japan, Canada and the US provide different guidelines. I wonder if Japan's recommendations come from shorter drives? Or Canada's recommendations are due to colder temperatures? And in that vein, SoA had to make a blanket statement for the US, where there's both city and country driving, and temperature extremes, that covered the bulk of typical usage? Maybe there isn't a technical/rational decision for it (i.e. political or financial),

 

My current vehicle has a ZF8 transmission which isn't without it's own controversy. It's used by 10+ major manufacturers which (to my knowledge) claim it has "lifetime" fluid, yet ZF suggests 80-100k OCI's. Go figure.

Here is an interesting video on the basic CVT fluid change procedure. Whilst it may not be totally specific to 6th gen Legacy, I think there is enough pointers contained in it to satisfy most DIYers on this forum.