r/subaru • u/Strqtegy • 8h ago
r/subaru • u/Chippy569 • Jun 04 '24
Mechanical Help CVT Fluids: A Consolidated Thread
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
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 • u/Chippy569 • 12d ago
What questions do you want to see answered in the Wiki FAQ?
Hey all,
I've been (slowly, admittedly) updating the r/subaru wiki to get as much useful reference info into one place as I can. I initially added a page to add in an FAQ section, for topics we regularly see, with the intention that there is a single simple place to send people to for regular questions. Ideally we can add it to the sidebar when it's fleshed out.
What sort of topics would you like to see covered in the FAQ?
r/subaru • u/Falkitos • 6h ago
Buying Advice Advice on buying an abandoned GC8
Hi! Last year i found an abandoned blue GC8 near my town, and it broke my heart to discover it is an RX 2000. We got other years of the GC chassis here in Brazil, but only 10 of this model were imported in the year 2000. The owner has it since new, and made every early 2000s mods you can think of. Those horrible Altezza tail lights, "carbon fiber" wrapped roof, trunk, and hood, etc. Apart from the tail lights, its a really beautiful car. Before being parked there, it had around 370 horsepower, front mounted intercooler, antilag, Fueltech ECU, Launch Control, Boost Control, and enough torque to make 1st and 2nd gear die. Now the gearbox sits in the trunk, half disassembled. Car was abandoned almost 10 years ago.
Would it be worth it to fix this car? Something in my heart tells me to make it run again. It was a really good and famous car back at its prime, even was the cover for a magazine about tuner cars in the early 2010s. It would be a shame to let a car with so much history just rot and die like that.
r/subaru • u/Zanna-K • 17h ago
Word to the wise about buying used turbo Subarus
Spent a bit of time this evening unfucking yet another "Racing Inspired Cosmetic Enhancement" that the previous owner did. This is the duct that is responsible for 100% of the airflow into the top-mounted intercooler on an SJ (2014-2018) Forester XT. The intercooler is responsible for cooling down the air charge generated by the turbocharger.
On the bottom is the modified part - he cut HUGE holes in it, cutting the amount of directed air by a third to a half, decreasing engine performance significantly and increasing the chance for knocking and pre-ignition. All just so they could mount bright yellow and blue Hella brand car horns in a higher, more visible position.
This is why people hate buying used performance Subarus. If you're going to do it, just go into it with eyes wide open if you see any signs of modifications and ESPECIALLY if you're not familiar with working on cars yourself. I had a WRX which is like 90% the same mechanically so I'm mostly aware of how everything fits together but this one slipped past me for the longest time because the WRX has a good scoop for the intercooler while the Forester doesn't.
r/subaru • u/cheap_chalee • 12h ago
Saw this at this year's JCCS in Long Beach. Does anyone know if the owner has an IG?
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Subaru Generic 05 Legacy GT is really choochin along
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Found this little guy at our local dealership.
r/subaru • u/akaThirteen • 3h ago
Mechanical Help PSI no longer shows numbers after hitting pothole
I hit a gnarly pothole yesterday and after that on the tire pressure screen it no longer shows the PSI of any of my tires and the tires on the screen are now yellow color. Ive used gauge to check the tires and PSI is okay. How concerned should i be?
r/subaru • u/Atomic-pangolin • 5h ago
How do the cloth seats hold up?
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r/subaru • u/pliskin414 • 4h ago
Mechanical Help What kind of headlight bulb clip is this? 2012 Forester
All the videos online have a clip that fastens to that front knob, and it looks soooo easy to unclip. I can't for the life of me figure out how to unclip these two side holders without three hands.
The other headlight has the standard type I'm used to.
r/subaru • u/NotABot2123 • 11h ago
Subaru Outback 2007 LL-Bean 3.0r
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r/subaru • u/Time-Refuse666 • 15h ago
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Found this awesome looking Legacy GT. 133k miles. They're asking 5K. Could probably talk them down a bit. Thoughts?
r/subaru • u/Rod-Serling-Lives • 16h ago
A Subaru properly enjoyed (apologies for the poor blurring, I'm no editor).
r/subaru • u/ifixtheinternet • 3h ago
Mechanical Help What might this noise at startup be?
2013 Legacy 3.6R - 110k Wondering what this ticking / rattling noise is at startup. Seems to dissipate once the car is warmed up. Replaced the accessory belt, tensioner and idler pulley about 100k.
Normal?
Hope i'ts not the timing chain 😬
r/subaru • u/Lost_Television_3341 • 24m ago
Buying Advice 2018 Legacy Aftermarket Radio Suggestions - HELP
Hi all,
I've decided to go aftermarket radio in my 2018 Subaru legacy. Has anyone else taken this route? I am looking for suggestions for aftermarket radios that have wiring that is fairly friendly to the factory wiring while playing well with Subaru and its crazy starlink features. So far, I am leaning towards this one: 9" Qualcomm Radio for 2015-2018 Subaru Legacy Outback Support Harman/Kardon AMP | eBay. Please let me know if you have any suggestions. I ultimately just want to have a radio in the car since mine has the "ghost touch" delaminated screen. Thanks.
r/subaru • u/peltor_streams • 34m ago
Car Mods Anyone in here know if this would fit a 1986 leone?
r/subaru • u/Fix-Hefty • 40m ago
rebuild vs fresh shortblock
Just looking to get some opinions regarding rebuilding an ej255 with roughly 300k or getting a fresh shortblock and just having the heads redone and going with brand new internals. (there were not issues with the car apart from leaking oil which i believe the headgasket started to go, regular maintenance was performed a no mods done to it. It is now going to be a project car )
r/subaru • u/Accomplished_Drop596 • 1d ago
22b?
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r/subaru • u/Scholar-After • 51m ago
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r/subaru • u/Right_Focus1456 • 5h ago
Windshield Program Support email
Anyone else get an email from Subaru Canada Dec 14 2024 offering compensation for cracked windshields for the Outback? My email is flagging it as spam, but it looks legit.
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If this thing is legit, they said to still submit and it will be reviewed. Worth a try!