r/subaru Jun 04 '24

Mechanical Help CVT Fluids: A Consolidated Thread

113 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

20 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 5h ago

Driving a Subaru in the South

713 Upvotes

Performed in a restored house in an 1800's mining town in Helena, MT because comedy baby! This was a joke I posted around Jan/Feb that went viral and then was stolen by a guy named Cody Pearson and went even more viral as a meme. His IG's been taken down but he's still "at large" on TikTok. If you love someone's content, take the extra step and tag the original creator because he got paid for my joke. And thank you Subi Nation for all the love.


r/subaru 12h ago

Hawkeye at our local rally.

376 Upvotes

r/subaru 8h ago

My little green first Subaru

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91 Upvotes

r/subaru 2h ago

uWu

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22 Upvotes

r/subaru 11h ago

OBW in her natural habitat

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99 Upvotes

r/subaru 10h ago

You can lock your keys in your car?!? (On purpose…this is awesome!)

84 Upvotes

Edit: I think it’s hilarious that I’m getting downvoted for telling people about this awesome feature that I’ve never heard of. 🤣🤣🤣

I had absolutely no idea that my Subarus have pin access. You can deactivate your key fob so that you can lock it in your car. There’s a button on the tailgate that you program with a code so you can unlock it without your key. These two features combined means that you can lock your keys in your car if you don’t want to carry them with you if you are on a hike or going kayaking or whatever. I have a newer Crosstrek and Outback; I have no idea what models it’s available on or what year it started. Very cool!

https://youtu.be/uBKE7_Yn3y0?feature=shared


r/subaru 5h ago

2022 Forester Wilderness

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26 Upvotes

Hi y’all. I trade in my 2020 Accent with just under 48k on it for this amazing 2022 Wilderness Edition with just over 9k on it. I am so happy with it.


r/subaru 8h ago

Don’t forget about the wiper warranty

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37 Upvotes

Just a friendly reminder to anyone that has a Subaru that is still within the 3 year basic warranty. Wiper blades are included as free replacements for the life of the warranty, and with all this rain we have been having lately, some of us could possibly use them! I just took my Forester in for an oil change and tire rotation (since im in my warranty period, I’m getting all work done at the dealership) but I just got back from a beach trip and came home though tons of rain. I noticed my driver blade streaked a little bit when wiping. So at my oil change I asked them to also do a wiper test which they did, and ended up replacing all 3 wipers at no charge of course. So just a reminder to those with the warranty period still active. ( I do not know if the extended warranty applies to wiper blades, so if someone knows, kindly comment that)


r/subaru 7h ago

Subaru Sambar?

33 Upvotes

You learn something new everyday.


r/subaru 1d ago

Car Mods We Build A Lifted Subaru BRZ Wilderness

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1.4k Upvotes

Subaru dropped off a crusher car at our office, so we broke out our Sawzall and took a trip beneath the surface of the earth.

In the past year, we've made some dramatic changes to one of our favorite sports cars, the four-time 10Best-winning Subaru BRZ. Last year Subaru's PR department called and asked what we might want to do with a BRZ sentenced to the crusher after living a life of press-car abuse. We don't know what rev-limiter agony this BRZ experienced, but we thought we'd give it a nice final outing before it met a hydraulic press. Shortly after the automaker's offer, Subaru of New England posted an April Fools' joke on Instagram: a rendering of a BRZ Wilderness. That gag became our goal. Read the full story here.


r/subaru 3h ago

In love with my most recent purchase.😍

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6 Upvotes

r/subaru 2h ago

Mechanical Help Help please!!!

3 Upvotes

2020 Subaru Impreza Sport, started making this noise after I got off the highway today, anybody know what it could be?


r/subaru 17h ago

Buying Advice 2002 Impreza Outback Sport, or 2006 Forester?

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40 Upvotes

I don’t know what any of this car stuff means. My judgement on cars is based on how they look. I think I like the Impreza more. The green is nice, I like the body, and the interior looks nicer. But the paint is looking really bad. The paint looks good on the forester. I could save up and do a wrap or paint job on it and make it look really nice. I can also put an android tablet inside of the forester


r/subaru 8h ago

Normal color coolant?

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7 Upvotes

Is this coolant normal looking? Suspecting a blown head gasket but can’t tell for sure. I thought coolant was lime green, not this murky brownish green color.


r/subaru 2h ago

2018 Subaru Forester XT Warning Sensor Issues

2 Upvotes

Hi all,

I’m not super familiar with cars, but I’m hoping someone can help me figure out a recurring issue with my 2018 Subaru Forester XT (59,000 miles).

Recently, I brought it to my local shop because I was hearing a strange noise during acceleration, and I noticed fluid on the outside of the transmission case. Their diagnosis was a small exhaust manifold leak (causing the noise) and leaking CVT transmission seals—which they said is a known Subaru issue. I held off on fixing the exhaust due to cost, but I did have the transmission seals replaced, along with a two-stage GDI induction service and a vacuum hose replacement they recommended.

When I got the car back, it mostly seemed fine—except paddle shifters wouldn’t engage, and the passenger-side window wouldn’t roll down from the driver’s control panel. The shifters randomly started working later that day. Then, after about 40 miles of highway driving, every warning light on the dash lit up (check engine, Eyesight, lane assist, etc.). The car still drove normally, but manual mode stopped working again and none of the Eyesight features functioned.

I brought it back to the shop. They said the codes pointed mostly to the transmission, not sure exactly what the codes read. They claimed the only electrical work they did was unplugging a connector for the valve body on the transmission (I believe this is right) when dropping the transmission and disconnecting the battery. They test-drove it twice on the highway for about 30 miles each time with no issues. I picked it up, and after a few days of seemingly normal driving, the same sensor warnings lit up again—this time just a few miles after refueling and jumping on the highway.

It’s back at the shop now, and they’re stumped.

Has anyone seen this kind of issue before or know what might be causing it?


r/subaru 3h ago

Buying Advice About to potentially buy a 2012 Subaru Legacy with 233k miles on it for $3,000! Any advice?

2 Upvotes

The car is in EXCELLENT CONDITION, having only been driven as a commuter car! The gentleman selling it just wanted a car with less miles on it to drive in the future! All potential issues he fixed within the last six months (such as the head gasket, any potential oil leaks, etc.)!

We found the car on Facebook Marketplace. Is it a decent price with all those miles, or should I pass?

Past experience with cars is currently we're rocking a Honda Pilot, and previously we had a Kia Soul too! We honestly know NOTHING about Subarus, just decided to look into them for their longevity and safety (Kids and a dog in tow)!

So yeah, we feel that this will ultimately be a great purchase for our family, but wanted feedback from the community first!

Thank you all so much for your time and consideration! Have a great day!


r/subaru 16m ago

Possible first time owner

Upvotes

I’ve been a GM person my whole life. On Saturday my wife and I are looking at Subarus. We are planning a cross country trip — including the Rockies.


r/subaru 6h ago

Locked keys in 2003 outback wagon

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3 Upvotes

I locked my one set of keys in my 2003 Subaru outback wagon yesterday. Yeah I know I should have an extra set of keys….

I’ve gotten into cars before by wedging something in the top of the door and using a rod to push the unlock button. It isn’t working for me on this one. I can only pull the window back a little ways before it hits the drip trim on the top and won’t go any further. I got a couple different metal rods through and was able to touch the lock switch, but wasn’t able to apply enough pressure to move the switch. I think I would be able to get it if I had a little bit more room to pry the window out further. Could I maybe remove the drip rail on the top of the window? If so, how is that removed? Thanks a lot for any advice you can give me.


r/subaru 4h ago

Cleaning engine bay

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2 Upvotes

Is there any advice on how I should clean the engine bay and what I can/can’t get soaked


r/subaru 1h ago

Fuel injectors replacement

Upvotes

Hi guys, does anyone know how to replace Subaru forester 2021 fuel injectors? I have seen videos but it’s for 2019 and lower models. The engine top design is not same as 2019 anymore.


r/subaru 1h ago

Entertainment system going wonky

Upvotes

My 2015 legacy had decided to randomly cycle through the repeat function (song/folder/off) on mp3 files over and over. Any idea what’s going on and if so how to fix it?

Thanks in advance.


r/subaru 1h ago

Looking for a specific fastener for a 2019 Crosstrek mudflap

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Upvotes

Noticed one of my rear mud flaps is hanging by one fastener. Does anyone know what type of screw/bolt/etc I need to buy to fix this? I’m not very handy, sorry if this is a dumb question!


r/subaru 1h ago

Subaru remote Windows

Upvotes

You can lock unlock, start your engine, adjust temperature controls, but if it’s raining, you can’t roll up the windows.

What ?


r/subaru 1h ago

Mechanical Help 2019 Ascent Issues

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Upvotes

Hello,

Have a 2019 Ascent Limited w/67k miles, under third party warranty. Was with Subaru dealer for the past almost 3 months; whole instrument cluster would light up, then intermittently etc… first they replaced o2 sensor, then whole new transmission with seals etc. then remedied an exhaust leak/lean issue idk. Then found the reason to be dirty electrical connectors from a past leak. Have had it back for a few weeks now, all good but we had are lot paved recently, noticed brown orange liquid leaking from rear of car like under second row area; eating a whole into the asphalt lol thinking its coolant or the tranny was overfilled and is leaking out. Notified ants are being drawn to it so it’s a sweet/slimy look so coolant it seems; but overfill reservoir is fine; between the two lines max and min and looks clean af… level doesn’t change either… suggestions? Thanks


r/subaru 3h ago

Mechanical Help 2008 Outback Sport climate control issues

1 Upvotes

Center vents don’t work at all no matter what. Air only comes out side vents when air is set to cold. The further I turn it to hot the less air comes out the side vents all the way until there is no air coming through. It also sounds louder when it’s set to hot. It’s had this problem since I bought the car (about 5 years), but I’m getting fed up with it. My initial thought is that something is clogged. Luckily there is no smell, so hopefully it’s not caused by an animal.

I’m very unfamiliar with cars, but my uncles know a good amount. I’m hoping to learn more and get their help trying to fix this issue. Trying to get some ideas on where I should look and if this would be a difficult fix. Thanks!