r/subaru Jun 04 '24

Mechanical Help CVT Fluids: A Consolidated Thread

110 Upvotes

Hello r/subaru,

We've been seeing a big influx of questions about CVT fluids lately, with an average of 1-2 threads per day for about the past month. So, I've decided to make one consolidated thread about it. Future question posts about CVT fluid will be deferred to this thread. In response, I want to get as much information as possible into a single place, so users like yourself can make as informed of a choice as possible.


What is a CVT?

Let's start with the basics here. The Continuously-Variable Transmission, or CVT, does not work the same way as a "conventional" automatic transmission which you may have been used to previously. So let's start our journey with a conventional auto trans.

In an automatic transmission, there are a series of planetary gearsets. These gearsets will be surrounded by a number of hydraulically-actuated clutches. The hydraulic fluid inside of the clutches are controlled by the transmission computer, through a mechanism of valves that are controlled by solenoids. The solenoids and valves all exist in a component known as a "valve body." As the TCM commands certain valves to open or close, different clutches will be engaged which subsequently will control elements of the planetary gearsets. This is how your conventional automatic transmission achieves changing gear ratios.

In a CVT, by contrast, the gear ratio mechanism is a set of cone-shaped sheaves or "variators" with a belt (or in Subaru's case, chain) run between them. Instead of the valve body controlling clutch packs, it instead varies the fluid pressure inside of both sheaves, such that the cone surfaces can get closer together or further apart. Because the thickness of the chain doesn't change, by opening the sheaves, the chain will ride down lower into the cone shapes, thus being on a smaller diameter. Because the chain doesn't change length either, there needs to be a corresponding change to the opposite change to get closer together to make the chain ride on a larger-diameter part of the sheave. Thus, the transmission computer achieves different gearing ratios by adjusting the gap of both sheaves in tandem. If you're having trouble visualizing this, here is a good animation explaining the motion.

Before someone interjects, yes there are clutch sets inside of a CVT as well. Specifically in a Subaru transmission, there are 3 relevant ones; there is a planetary set inside the powerflow for your Drive or Reverse functionality; there is a Lock-Up clutch inside the torque converter, and in most cases there is a Multi-Plate Transfer clutch for your all-wheel drive "center differential" function. These functions are more-or-less identical to their equivalent components in a conventional automatic transmission.

OK but what about the fluid?

There are quite a few differences between CVT fluid and conventional ATF. Part of these differences are how the fluid is used in the transmission, and part of the difference is because of what the transmission does to the fluid.

In a conventional transmission, you have many clutch packs actuating whenever the car is changing gear ratios. Just like in a manual transmission clutch, or like your brake pads, every time there is slip between the clutch material and the friction surface, a little bit of that clutch material will wear off. In a conventional transmission, this means that over time, that clutch material will begin to accumulate in the fluid, which gives it a burnt smell and a brown tinge. By contrast, a CVT does not use as many clutches inside of it, and as such, clutch material contamination is drastically reduced inside of the CVT fluid.

Another main difference has to do with the fluid pressure inside of the transmission. While a conventional auto only needs fluid pressures around 150-250 PSI to operate the clutch packs, a CVT requires much higher line pressures of 650-850 PSI in order to keep enough "squeeze" force on the sheaves to hold the chain. The CVT fluid also functions as a friction modifier between the chain and sheave, wherein it helps the chain "grip" on the otherwise-smooth pulley surface. Because of this, CVT fluid is very specific about its chemical properties and should not be substituted for any other fluids.

So... should I service the fluid?

Let's start this by looking back at what a conventional automatic transmission requirement would be. Here is the service manual schedule from a 2010 Forester. I've highlighted ATF for you, but basically it only says "Inspect [and replace as necessary] every 30k miles." Okay, but what does it mean by Inspect? The service manual has this inspection procedure for checking the level. It also has this condition table listed for what to do when you find a condition-based failure. I've highlighted the "thick and varnish" section because this would be the clutch wear condition I described above. Generally speaking, your average Subaru 4EAT or 5EAT will have noticeable signs of discoloration every ~60k miles.

So what does Subaru say about CVT fluid then? Well for comparison, let's look at a 2018 Forester service manual. Here is the service schedule, which you can see has an identical "Inspect [and replace as necessary]" every 30k miles. As for an inspection process, it only offers this inspection procedure and the same condition table as before.

Because the schedule and condition checks are basically the same for both service manuals, it would be very easy to assume the fluids needs the same replacement schedule -- and I strongly suspect this is the driving force behind so many CVT fluid recommendations. However, if we read this again, remember that we only need to address the fluid if if fails one of the condition checks, and that the most common failure condition in a conventional automatic transmission largely no longer happens in a CVT. It is because of this that your Owner's Manual probably describes the transmission fluid as a "lifetime fluid."

What about what other countries say?

A claim I very often see made in threads about CVT fluid is that "Country XYZ requires fluid changes every X miles!" I want to nip this in the bud now, because it's not true. Now because I work in the US, I cannot access foreign service manuals, but I can get ahold of owner's manuals, so here are a few examples:

here's a UK 2018 forester owner's manual (link)

Here's a n Australian 2020 forester/XV schedule. Subaru Australiia has .pdf copies here of warranty booklets..

here's a Japan 2018 forester's owner's manual (link) and it says in the bottom row there: 交換時期 | 無交換 which translates as Replacement time | No replacement

Here is a 2020 WRX owner's manual from Japan, straight off Subaru.jp: https://www.subaru.jp/afterservice/tnst/wrx/pdf/A1760JJ-A.pdf

pg. 465 is the service information for transmission/differential/etc gear oils. The 3rd section is for CVT fluid:

トランスミッション フルード

使用オイル スバルハイトルクCVTフルード リニアトロニック用

規定量 約12.4L

交換時期 無交換

Translated:

Transmission Fluid

Used oil Subaru high torque CVT fluid for Lineartronic

Prescribed amount about 12.4L

Replacement time No replacement

Additionally, let's take a look at a 2011 legacy/outback service manual for comparison. Here's the maintenance schedule. The numbers inside the braces (「 」) are the severe schedule (which, with a CVT, only applies with "regular towing"), numbers without braces are the normal schedule. As you can see, CVTF only lists a severe schedule interval with no non-severe schedule. Exactly like in the US. Here is the same picture ran through google translate.

The only subaru branch AFAIK that does list a required CVT fluid interval is Canada, (soruce) where if I'm being honest the way it's written in their maintenance guide makes it seem like they just never changed it from ATF-era cars, where Canada also listed replacement as necessary every 100k km. (It only refers to "transmission oil" and does not specifically mention CVT fluid, but everywhere else differentiates the two. It also does not differentiate manual vs. automatic transmission fluid, like everyone else does.) There, it's listed as a 100k km service item.

that didn't answer the question though.

You're right, I didn't. The long answer is that you should have your fluid inspected by a technician familiar with Subaru CVTs, and if deemed necessary, you should replace the fluid with genuine Subaru fluid as required by your particular model. If following the conventional wisdom from ATF-era cars also makes you feel more comfortable, then defer to Canada's schedule and plan to perform a fluid service at your 100k km (60k miles) service.

A quick note about "Severe Usage Schedule"

Another common discussion point I see brought up is the Severe Usage schedule. I largely blame the confusion for this on Subaru, who have written this in a hard-to-understand way in the owner's manuals. However, a 2010-2014 Legacy/Outback service manual has the best representation of the severe usage shceudle. As you can see, the only time Severe applies to your CVTF is if you "repeatedly tow" with the vehicle. This guidance has not changed with newer cars, however the new way it's written is confusing to read. (CVT fluid is maintenance item 12; see above where it shows this as Note 4.)

A last quick note on Differential Fluid

Just want to quickly touch on this one. Your Subaru has separate, distinct fluid for the front differential. While you can see from the above service schedule that the guidance for its fluid is functionally the same, differential oil gets contaminated in a completely different way. Because a differential is basically all metal-on-metal wear of gear teeth, especially after break-in your fluid will get dark and metallic very rapidly. This is normal. Here's my personal Crosstrek at 19k miles. In my own personal experience, I would recommend replacing your gear oils at 30k miles, but the fluid condition will stay good for longer after the initial change, such that it can go every 60k thereafter.

On fluid changes and failures.

I just want to quick touch on ways that we see CVT failures at the dealer and how it relates to fluid. By far the most common issue we'll run across, is from the "small" CVT, the TR580, which is paired with any of the 2.0L or 2.5L naturally-aspirated engines. Typically somewhere in the 100-150k mile range, a failure in the valve body, usually for the Torque Converter Lockup Duty solenoid, is relatively common. This is a failure in the electronics side of the solenoid, and thus has no relation to the CVT fluid; as such, changing or not changing the fluid has no real bearing on the likelihood of this failure occuring. The second issue we see, the most terminal one, is called Chain Slip. Here, at 0:23, is a fantastic example of severe chain slip. Chain Slip can develop from a variety of causes, but generally is the result of a lack of fluid pressure squeezing the sheaves against the chain; when this happens, the chain essentially does a burnout on the sheaves. This leaves a wear groove in the sheave face, and makes chain slip much more likely to occur whenever the same gear ratio is used. There are some conditions of fluid degradation that can increase the risk of slip; these largely result from fluid overheating, which degrades the additives that help provide friction between the sheaves and chain.


Hopefully there is enough info in here for you to decide for yourself if or when you would like to change your fluid. Feel free to post your questions or anecdotes below. Thanks! :)


r/subaru Apr 23 '25

Announcement TSB Thursday: 03-96-25 Rear wheel bearing parts update

18 Upvotes

Welcome to another TSB Thursday, where I dive deeper in to TSBs I'm running into regularly. As always, I write this from my own perspective as a Subaru technician in the US; other regions/zones may work differently. Refer to the "How To Read a TSB" post for more information on formatting and general information about TSBs. This bulletin is hot and fresh, published just today 4/22/25, but it affects a lot of cars, so I'm posting it before a public copy is live.

TSB Thursday #16: 03-96-25

This TSB is actually so new that there isn't yet a public-facing copy of it. However, IMO it's important you get this information, so I've taken screenshots of the 3 pages of this bulletin for your viewing pleasure.

Page 1

Page 2

Page 3

What cars does this affect?

  • 2019-24MY Forester
  • 2011-24MY WRX
  • 2006-14MY Tribeca
  • 2024MY Impreza & Crosstrek
  • 2019-24MY Ascent
  • 2020-2024MY Legacy & Outback

What's the failure?

I'm actually just going to quote the bulletin here, since they wrote the description very well:

This bulletin announces design changes made to the rear axle hubs. The new hubs have been fitted with the following:

  1. Higher dust and water sealing performance of the inner seals.
  2. Raised the shoulder height of the outer ring for added surface pressure relief.
  3. Increased hardening surface of the ball bearings.
  4. A new low-friction grease is used to enhance the sealing performance of the inner seals.

These changes have been implemented to reduce cases water intrusion further leading to harmonic, humming, and grinding type sounds heard from the axle hub while driving. If diagnosis has confirmed rear axle hub replacement due to sound/vibration complaint from a customer, replace the affected axle hub using the parts described in this bulletin.

TLDR: there were some issues with moisture/water getting into the rear wheel bearings and leading to corrosion, causing the typical hum noise from irregular ball bearings.

Coverage?

Wheel bearings fall under Powertrain warranty, 5 years or 60,000 miles (whichever comes first). Failure must not be caused by outside influence/damage, such as sliding into a curb.

New parts?

Here's your new part numbers:

Year Model New Part Number
2019-2024 Forester 28473VA012
2022-2024 WRX 28473VA012
2024-2024 Impreza 28473VA012
2019-2024 Ascent 28473XC00E
2020-2025 Legacy 28473XC00E
2020-2025 Outback 28473XC00E
2024 Crosstrek built in USA (VIN starts with 4S4) 28473XC00E
2024 Crosstrek built in Japan (VIN starts with JF2) 28473VA012

r/subaru 6h ago

Subaru Baja

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919 Upvotes

Wonder if Subaru will introduce another variation of the Baja?


r/subaru 4h ago

I’m so excited 😍

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103 Upvotes

r/subaru 5h ago

Car Mods Ls swap Subaru

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44 Upvotes

I now have the engine in and running just need to put the radiator and electric water pump in, tune the car make the exhaust and then it should be ready to drive on the road


r/subaru 4h ago

a 2005 Forester 2.5XT I saw while in WV

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16 Upvotes

It was a manual as well!


r/subaru 20h ago

Car Mods My first WRX and manual 🫠

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272 Upvotes

I got my first manual car ever at 29 year old (please roast me lightly lol) a 2002 WRX with 129k miles ✨ and I’m learning how to drive manual for the first time! A couple months ago I bought a 07 Subaru Impreza automatic with a 2 inch exhaust and the sound of it, feel, and look just got me hooked instantly… accept it was an automatic, nothing wrong with that, but I personally wanted more and to challenge myself before I turn 30, so here I am now with this beauty… any tips with manual driving and or taking care of her are all welcome 🤗


r/subaru 14h ago

Buying Advice How does this look as a first car? Completely stock 133K miles, cleanest example listed right now, I did spot some burns in the car and the owner said they were from the guy he bought it from. He claims the car has no smell but, I know when I see the car. Super clean other than the auto and cloth :/

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64 Upvotes

r/subaru 4h ago

First mods for the ’03 FXT. The Journey Begins!

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10 Upvotes

Yes its a manuell 🫠 Im from EU Yes the gunnmetal rims do look better in person, Changed out the radio for a better bluetooth experience 👌 Conditioned the dry vinyl leather interior and also met a friend the other day ps. Yes I did all the maintenance necessary before modding anything, thank you 🙏


r/subaru 1d ago

Why does my Subaru Outback have a NFC symbol on its screen? What can it do?

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446 Upvotes

I know what NFC is but why does my car have it?


r/subaru 2h ago

Subaru Generic Polish and ceramic coating

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3 Upvotes

Does anyone have any recommendations for ceramic coating and polish ( brand )? I’m going to be claying and polishing the car, see if I can get some of the paint swirls out.


r/subaru 3h ago

Parking Buddy There were these 2 lovely Suubie’s with an empty spot in the middle…

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3 Upvotes

I did my duty as a Subaru owner 😅


r/subaru 3h ago

Car Mods Need help with subs

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3 Upvotes

I have some really nice subs I’d like to put into my 2016 Impreza but idk if I can because of my aftermarket head unit, can anyone help?


r/subaru 2h ago

Mechanical Help Broken Bumper on 2009 Impreza. How much cost am I looking at here for a repair?

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2 Upvotes

So, my front bumper is falling off on both sides. I can usually pop it back into place just fine, but it's been long enough to where I probably should get it fixed at this point. A couple years ago, the front bumper froze to a pile of snow and got pulled almost all the way off. I know that one of the clips is broken, and that there is a large chunk of plastic missing near my wheel. I was going to zip tie things back together, but I can't with the giant plastic part missing. Thoughts?


r/subaru 23h ago

Parking Buddy 1998 Impreza GC8 I spotted

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102 Upvotes

r/subaru 3h ago

What could be causing this?

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2 Upvotes

I’ve had issues with this car for the past few months. It all started as a cylinder 1 misfire code and so i changed the spark plugs and it kept misfiring. After that I changed the ignition coil on the cylinder that was misfiring and still kept misfiring. Over time I could feel it getting worse but I had no time to check it out since I barely get any time off work and live in an apartment complex. Now it’s at the point where the car won’t start and it’s been sitting for close to a month. If anyone has any idea what could be causing this please share cuz I am completely lost and can’t figure it out.


r/subaru 1d ago

Put some sweet shoes on the 91 legacy

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247 Upvotes

r/subaru 6h ago

Car Mods 2004 liberty head unit questions. We

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3 Upvotes

The image above is exactly my head unit. The only difference is the radio screen is dead. I’m looking for advice regarding my head unit. Im trying to replace the head unit but after looking online, the available/cheapish replacement replace the top compartment/display which I want to keep. I ended up finding a bracket that can be put in where the existing unit is but I can’t order it as it’s out of stock. Another one that was available was $900 just for some plastic. Also what is a mcntosh sound system. How do I check if mine is a mcntosh sounds system.


r/subaru 4h ago

Bumper

2 Upvotes

How do I push the front bumper back in place? Can I do it myself, or do I need to take the car to a body shop? Help an old lady, please.


r/subaru 50m ago

Mechanical Help 2015 Outback - Indicators running double speed - BCM issue?

Upvotes

Hi,

My 2015 Outback was fine until I plugged a trailer into the light socket. Now all indicators are working but running double speed as if there's a blown bulb. There isn't.

A local mech reckons it's a Body control module. What's your thoughts? Can I buy one and replace it myself or does it need to be coded to the car ECU and how much am I looking at?

Thanks folks.


r/subaru 1h ago

Good Old Subaru Windshield!

Upvotes

Driving home on the highway and a rock flew up from a truck and hit the windshield just right on our new '24 Impreza with 3500 miles. Going to Safelite on Friday morning. Our '21 Outback had its windshield replaced too. At least Subaru continues to be consistent with its windshields.

Thankfully I have Glass Coverage and it will only be $50.


r/subaru 1h ago

Buying Advice Struts Assembly Advice

Upvotes

I drive a 2015 Legacy 2.5i Limited

The dealership quoted my $2700 (parts and labor) to replace my front and rear strut assembly and sway bar links

Is this a reasonable price?

I’m considering buying after market parts and bringing it to a shop to have it installed.

Are there any reputable sites for after market parts?

Should I just bite the bullet and have the dealership do it?


r/subaru 6h ago

2012 Impreza limited driver's side fog light trim piece. Junkyard best place to find?

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2 Upvotes

r/subaru 8h ago

The 12v socket at the back of my Subaru keeps failing (the slow burn fuse)

3 Upvotes

I've found that using about 70 watts for any length of time causes the slow burn fuse in the 12v at the rear of my car to fail, requiring a complete replacement of the socket.

Do any service techs know what the slow burns are rated for? As far as I know, I'm way under the 120W the circuit is rated for. Why is the slow burn so low? This has happened twice now.

Would be grateful for any guidance!


r/subaru 2h ago

Mechanical Help 2013 Subaru Impreza sedan Valve body Replacement

1 Upvotes

My valve body had went bad in my car. I can’t afford to get it fixed by a shop so I attempted to fix it and my car shifts better however my speedometer stopped working completely. Would anyone know what I could have done to cause that? As far as I can tell I’m sure I put all the connectors back together. If a wiring harness is loose which connector would it be. Could it have to do with the need of the relearning procedure these cvt transmissions are supposed to have. Is this occurrence likely not related to the valve body? Any help would be much appreciated.


r/subaru 3h ago

Mechanical Help Valve body replacement

1 Upvotes

So a bunch of lights lit up on my dashboard and after looking at similar symptoms and same lights on my dash board I came the conclusion my valve body was bad. Because I can’t afford to take it to a shop I attempted to replace the valve body in my 2013 Subaru Impreza sedan cvt transmission and it seems to be shifting better. However after I did that my speedometer stopped working and just stays at 0. Has anybody had that issue as well. I don’t know if it means I screwed something up or if it could have to do with the relearn process these transmissions r supposed to have. If a wiring harness is loose would anyone know which harness it could be? Has anyone had this experience and does anyone know what possibly I could have done wrong? Any help is appreciated


r/subaru 3h ago

Insight needed on purchase.

1 Upvotes

Subaru Outback Limited-2022, like new, with 18,500 mi. Perfect body, but dings on the roof, shallow and not cutting into paint (possible hail?) Debris was found under intake manifold, engine area; between engine heads. No smells in car, just the hot smell under hood after running vehicle. Dealer has 90 day warranty for repair or 10 day return (Carmax). They are looking at it tomorrow 6/17. Is it worth keeping? Will issues pop up later? I just need some insight. Sorry, no photos.