Subaru Forester Owners Forum banner

21 - 40 of 66 Posts

·
Registered
2015 2.5i Premium
Joined
·
1,304 Posts
I had my CVT go twice on my 15 2.5 around 19k and 22k. One reason I am going to get rid of mine at 100k is because the CVT went twice within a few months. That shook my faith in it quite a bit. If it had only failed once, I probably would not even worry about it and at 100k, just keep it as a secondary vehicle. I am now at 45k and so far so good.
 

·
Registered
2011 Subaru Forester
Joined
·
422 Posts
I don’t know about the value but don’t forget that if your CVT grenades you have an option to get one out of a junker. Sometimes Subaru Corporate will also give you a discount off the bill.

Furthermore, if you consider you have a solid car worth “x” and in 10-15 years it is “x-CVT”, you can replace the CVT as described above even though it may be close to the cost of “x”, but it would still be less than another $35k-x car payment.
The problem is there are not many junked Subies of that vintage and the ones wrecked in collisions are probably rather iffy replacements. And sadly when the car is 10 years old, putting more money into it than comparable used ones sell for, is going to be a very rare occasion.
 

·
Registered
2009 Legacy
Joined
·
912 Posts
The following is a bit long but it needs to be in order to explain it. This happened about a month ago. Do with it as you will. I am actually a bit reluctant to post this because many won't like this but feel it is important enough to hear:

I think the Achilles heel with Subaru CTVs are the solenoids.

Regarding the control of them, the TCM controls the solenoids but has no feedback as to position It does measure temperature.
Codes related to the valve body, where the solenoids live, are bout them being low (ie. "Shorted") or high ("Open").

Within the Subaru CVT, some solenoids are modulated so they behave like a linear actuator:
An linear actuator has proportional control over something. "Proportional" means you need something more than just an on/off state. You can control the position of that control by applying a signal to drive it there - they behave more like hobby servos you may see in RC cars, etc. A rudder servo doesn't just give you left/right actions but positions in between.
An actual linear actuator moves something linearly - not just between position 0 and 1. Solenoids really only have two states so how do they get two states from something like a solenoid?
The way they fixed that is by driving it between 12V and zero for very specific times - that's called "duty cycle". For instance, a 50 percent duty cycle means it drives 12V then 0V, 12V, 0V at a specific rate - let's say they do this 1000 times a second.
The Lockup Duty solenoid controls the position of the lockup valve. As the TCM determines where the valve should be, it increases the solenoid's duty cycle increases so it gradually moves that valve where it needs to be.
With that duty cycle, they are driven just hard enough to move it towards "full on" but the plunger is pushed back when the voltage goes back to zero because of some spring action - in this case,the control valve.
If you generate this pulse train just fast enough (in our example of 1000 times a second), that solenoid finds a position where it maintains a fixed position because the solenoid can physically only move but so fast. That's what makes the solenoid act line a linear actuator.
But, since they are constantly modulated, they will need cooling. They are driven with a fair bit of current so do get hot. Without it, they'll only last but so long.

Recently we replaced the entire valve body on a TR580 to replace a faulty lockup solenoid.
Subaru knows about this issue, has issued recalls on only certain models that yet have the same transmission.
The solenoid is not available as a replacement part. Replacing a vale body (>$700) as opposed to a solenoid (<100) means Subaru is make money off of their wonky design so could this be the reason as to why this isn't fixed??
.. but I digress.

So here's our actual experience:
After a free engine recall that required engine removal, just days after getting the car back, the car threw a P2764 code - "torque converter lockup solenoid low" - meaning shorted.
The thing is: it wasn't shorted at 12.3 ohms when measured statically. The spec is 10-15 ohms. I suspect the PCM must have a way to measure current to determine a coil 'open' or 'short' condition. Not a big trick but 12.3 ohms isn't shorted, even to a PCM.
So we took it for a test drive, monitoring the lockup solenoid and temperature, among other things.
It would behave fine until the transmission got hot. It would then attempt to turn on the solenoid, detect a short and turn back off - so the pulse train would disappear, the valve would open, causing the engine to race. This was consistentl when the transmission was at 238 degrees, after a couple of minutes of mild driving.

Clearly the solenoid had an intermittent short that showed itself at some temperature. I think the transmission was allowed to over heat because the dealer didn't refill fluid when they pulled the engine out. In fact, their paperwork showed that they did not. They refilled oil and even wiper fluid but not CVT fluid. That box was not check so that makes you go "Mmmm..", right? Why not indicate you refilled fluid that costs you 15 bucks but do check the box next to filling window wiper fluid?
So, physically checking the fluid, it was two quarts low. They hadn't refilled what they spilled. Surprise-surprise. That's what caused the failure, imo.
The solenoid's coil is copper. Copper expands at direct proportion to heat so when exposed to a lot of heat, it expands a lot. Once it cools, the windings shrink and rub bare spots over time. That's what causes the intermittent short.
I've proven it with a heatgun on just that one solenoid - it goes to about 3 ohms once it goes above 230 degrees F.
Overheating likely this was caused by dealer's negligence but also bad design. Subaru knows this.

These solenoids are very sensitive to overheating and there's definitely a systemic problem with them. They will not sell you the individual solenoid but require you to buy an expensive valve body. Just a couple of years ago, before the extention of the 100K warranty on the CVT, they'd charge you 6K for a new transmission and would send your old transmission to Japan for dissection -- so you are the beta customer. Nice.
It smells like a head gasket debacle all over again to me.

That's my take. I won't buy another Subaru.
 

·
Registered
2014 Forester Really...?
Joined
·
18 Posts
Just an FYI, '14 XT sitting at 112k miles. No real problems to note (at least with the transmission)
Drain and filled once back at 60k but that was due to lack of information since this was the first vehicle with a cvt.
I'm about to perform a drain and fill to see the color of the fluid. After lots of reading I might be heading towards trading the car in to get a new one since I'm not sure how the vehicle is going to be. I'm trying to remember but if I'm right I should see metal in the drain and fill once performed and I will provide my 2cents of a mistake once the procedure is done.
 

·
Registered
2009 Legacy
Joined
·
912 Posts
I'm about to perform a drain and fill to see the color of the fluid.
The refilling is too specific to be insignificant, imo.
Here's the actual procedure for a CrossTrek. I'd imagine it is very similar for a Forester in being specific. May want to double check.

Also beware that the filler plug is an inverse socket. Road crap gets in there end so clean that out really well so your inverse socket seats well. The plug shouldn't be tight if they followed their procedure but ours was insane.
You don't want to strip that because it would suck a cat through a gardenhose. I'd imagine the transmission would need to come out to fix that situation.

CVTFill1.png CVTFill2.png

@HeyChris Thanks. Don't want to be alarmist but my findings certainly alarmed me.
 

·
Registered
2018 Fozie XT
Joined
·
73 Posts
Very good read. I hope they will start selling those solenoids and allow to replace cvt oil sooner.

Also, support tranny cooler add on.

Most without problem may be using car in cold weather and not constantly pushing cvt to over 230F.

In CA , just in summer month, i was constantly getting over 220 from stop-n-go or long drive >30 min at 88F-105F. Since getting tranny cooler, same condition, my cvt temp barely break 185F.

I now do a lot of trail ride but only hit over 235 once when climing steep hill over 40 min in 90+ weather. I change my cvt oil at 15k miles.
 

·
Registered
2011 Subaru Forester
Joined
·
422 Posts
Overheating was the cause of most Nissan CVT failures, and I have read it causes the same solonoid issue. The key to a longlived one is frequent changes of the CVT fluid, and proper level is critical. And when filling you have respect the temperature parameters. Easiest if you have a Torque app so that you can see the fluid temp. From what I gathered its especially important to change frequently if you live in hot climate, a mountainous area or you tow with it. And I have also read they do not like running for 5 hour highway runs without a cooldown. If you are going to do long road trips with it its probably best to stop every few hours for 20 minutes or so. But what do I know, everything I have read about them has discouraged me as a person who likes to keep his vehicles for 10 years or more. I kept my 06 Nissan X trail for the past 11 years because it did not have the cvt and was the last of the proper Japanese Nissans. I bought the 2011 Forester because it has the 4AT and a timing chain.
 

·
Registered
2019 Forester Premium Package 15
Joined
·
386 Posts
The following is a bit long but it needs to be in order to explain it. This happened about a month ago.
Thanks for your reply, it was pretty technical and I dig that.

I don't think they'd want to put themselves into that situation again (re: head gaskets). The CVT has been excellent for Subaru because they were previously not really "known" for good fuel economy in the 00's because of their 4EAT. This changed when they went with the lineatronic CVT and it was significantly more efficient - my 09 Legacy would struggle to get above 30 mpg highway, but my 11 Outback would happily chug along above 32-33 highway. While 2-3 mpg doesn't seem like much, it's important to a manufacturer for a fleet average, which is why I don't see the CVT going away any time soon.

When the "original" CVT's had issues back with the introduction in the 2010 Outback/Legacy, it didn't get added to the Forester line until 2014 - and then got 5 mpg highway higher. That's substantial.

My understanding:

Also, the original "problems" with the CVT were not servicable. As the Subaru CVT is built to specification and only found in Subies, the engineers wanted to see and reverse engineer the transmissions to find out what went wrong. As time went on, they noticed an uptick in torque converter issues in the 2010-2011-2012 Outbacks due to the design of the converter and changed it. Then, they noticed you can change out the valve body. The only thing to my knowledge that they can't repair now is the actual chain-and-pulley system that drives the lineatronic. In time, my expectation is that this will allow for individual solenoids to get replaced - and I agree, much better to do a $100 repair than a $700 repair.

It's also worth mentioning that due to my own detective work I've found that Canadian-spec CVT models have a mandatory CVT Fluid change interval of 100k kilometers, or roughly 60,000 miles which corresponds with "Major" Service that includes spark plugs.

We don't have that requirement in the US unless you're towing, and then it's a 40k kilometer / ~25k mile interval per our warranty book's footnotes on the side. Not even "Severe" service in city driving requires the fluid change, per the book.

If I planned to keep my Fozzy long-term, I would absolutely consider the 60k fluid change interval at great expense (I think they quoted me around $500-600 for the drain and fill when I inquired about it for my Outback).

But, fluid changes won't help if there's truly a design flaw in the valve body or solenoid issue. That being said, a $700 valve body job every 10 years is more reasonable than a $2500 head gasket job, but your mileage may vary.

I really, really hope they come out with an EV Forester soon, or I might have to look into other brands.
 

·
Registered
2019 Forester Limited
Joined
·
553 Posts
@Remco , very informative post. Thanks for posting. Overheating of electrical/electronic components certainly reduces life, and if extreme enough, can cause failure. When you say "...the TCM controls the solenoids but has no feedback as to position. It does measure temperature", is the actual valve temperature measured, the valve body, or are you referring to the general CVT fluid temperature? Curious as my background was thermal design/test.
 

·
Registered
2009 Legacy
Joined
·
912 Posts
@Remco , very informative post. Thanks for posting. Overheating of electrical/electronic components certainly reduces life, and if extreme enough, can cause failure. When you say "...the TCM controls the solenoids but has no feedback as to position. It does measure temperature", is the actual valve temperature measured, the valve body, or are you referring to the general CVT fluid temperature? Curious as my background was thermal design/test.
Thanks. I was frustrated with it happening on a relatively newer car.
The temperature sensor is located within the valve body so I'd assume it monitors some combined temperature of the fluid and body. The body would cool it some but that's likely some fixed thermal conductivity so they could just add that in to get the actual fluid temperature.
 

·
Registered
2009 Legacy
Joined
·
912 Posts
Thanks for your reply, it was pretty technical and I dig that.
..
But, fluid changes won't help if there's truly a design flaw in the valve body or solenoid issue. That being said, a $700 valve body job every 10 years is more reasonable than a $2500 head gasket job, but your mileage may vary.
Thanks.

Getting a linear action by pulsewitdh modulating a solenoid, you'd have to make sure that solenoid is up for the job under worst case conditions. I can't tell whether they did that but it certainly seems to not like being overheated.
I think a true linear actuator would be a far more of a bulletproof design but probably more expensive as well. They've come down a lot, tho. I've used them several times and they are not crazy expensive and work really well.
Regardless, they should make those solenoids available. Them not doing that, requiring you to buy a valve body, is only in their interest.

A fluid change wouldn't have saved this situation but fluid does lose its ability to cool over time so it stands to reason one wants to change it periodically. In the crossTrek manual it specifically states that is does not require service, unless under extreme service. Stands to reason; off roading and towing would do a job on the car.
Now some dealers say that it should be changed - even though the manual says not to.

Since they didn't foresee these sorts of issus, I'm not convinced they did their due diligence or serve any of our interests.
 

·
SeasonedStalker
2017 XT Touring in CBS HT CVT
Joined
·
83 Posts
Good thread Bill. I noticed some seeping coming from my HT-CVT the TR-690 at 43k. They changed the the faulty seal out ( there was a tsb ) and the seepage stopped. I really hope the CVT lasts.




Sent from my iPhone using Tapatalk
Hey Jon thanks for the input! do you have any documentation of the seeping as I may be experiencing the same thing. Also what was the TSB Im wondering if i need to have it performed as well!
Cheers,
Joaquin
 

·
Registered
Sahuarita, Arizona USA 2018 Forester Limited
Joined
·
1,942 Posts
Discussion Starter #35
It's also worth mentioning that due to my own detective work I've found that Canadian-spec CVT models have a mandatory CVT Fluid change interval of 100k kilometers, or roughly 60,000 miles which corresponds with "Major" Service that includes spark plugs.

We don't have that requirement in the US unless you're towing, and then it's a 40k kilometer / ~25k mile interval per our warranty book's footnotes on the side. Not even "Severe" service in city driving requires the fluid change, per the book.

If I planned to keep my Fozzy long-term, I would absolutely consider the 60k fluid change interval at great expense (I think they quoted me around $500-600 for the drain and fill when I inquired about it for my Outback).
Even though I live in the US, I plan on having a 60k mile CVT fluid service based upon the Subaru Canada requirement.
 

·
Registered
2018 Fozie XT
Joined
·
73 Posts
Actually, i found an interesting couple paragraphs in manual. one of them related to your question:
". Frequent driving of an AWD vehicle under hard-driving conditions such as steep hills or dusty roads will necessitate more frequent replacement of the following items than that specified in the “Warranty and Maintenance Booklet”. – Engine oil – Brake fluid – Rear differential gear oil – Manual transmission oil (MT models) – Continuously variable transmission fluid (CVT models) – Front differential gear oil (CVT models)"

So there goes for those who OFFROAD and don't change CVT often. I have done mine at brand new 15k miles with offroad before tranny cooler and cvt oil was black. I'm awaiting to do it again soon at 30k miles and compare the oil (after cooler-with much more offroad/trail rides in hot summer month).

I got to read more. :)
Where does the manual say not to change the CVT fluid?
 

·
Registered
18' 2.5 Premium 6MT
Joined
·
147 Posts
Thanks.

Getting a linear action by pulsewitdh modulating a solenoid, you'd have to make sure that solenoid is up for the job under worst case conditions. I can't tell whether they did that but it certainly seems to not like being overheated.
I think a true linear actuator would be a far more of a bulletproof design but probably more expensive as well. They've come down a lot, tho. I've used them several times and they are not crazy expensive and work really well.
Regardless, they should make those solenoids available. Them not doing that, requiring you to buy a valve body, is only in their interest.

A fluid change wouldn't have saved this situation but fluid does lose its ability to cool over time so it stands to reason one wants to change it periodically. In the crossTrek manual it specifically states that is does not require service, unless under extreme service. Stands to reason; off roading and towing would do a job on the car.
Now some dealers say that it should be changed - even though the manual says not to.

Since they didn't foresee these sorts of issus, I'm not convinced they did their due diligence or serve any of our interests.
Really interesting breakdown on using PWM to control the solenoid, very much like LED brightness is controlled. Considering the similarity, I noticed when LED headlamps first came into widespread use about 20 years ago the pulse rate tended to be too slow creating a slight stroboscopic effect if you waved your hand in front of your face for example. Subsequently this has improved by I assume more efficient transistors that can operate at a faster pulse rate without sacrificing too much efficiency.

I am curious whether you know what effect the driving wave form would have on either reducing heat or prolonging life span of the solenoid? Would a steeper ramp improve efficiency and reduce heat?

The CVT is a really interesting transmission with many inherent advantages but there is a reason the only actuators I really trust are my right arm and left foot.
 

·
Registered
2009 Legacy
Joined
·
912 Posts
I am curious whether you know what effect the driving wave form would have on either reducing heat or prolonging life span of the solenoid? Would a steeper ramp improve efficiency and reduce heat?
They drive the solenoids pretty hard with really fast slopes. It doesn't appear slewed ("slowed down") at all. The power used to drive the coil is really just a function of what's under the curve. So if you modulate at 50 percent with steep switching slopes, the energy required is 50 percent of what it would be if it was driven at 100% - really just the area under the curve. So if the coil is 12 ohms, driven at 12V, the current is 1A and the power is 12W. At 50 percent, the effective power is half of 12, 6W.
If the slopes are slewed (not immediate but slightly slowed down), the area is larger so the energy would go up by however large those slopes are.
Energy loss (in heat generated) is a function of the coil used.

The TCM modulates the coils pretty hard. The 12 to 0V transitions are fast.
In fact, because this is a coil, when it is turned off, there's a fair bit of back EMF generated when the thing is turned off. At the risk of boring you with the details, when you apply a voltage to a coil and take it away, the coil 'wants' to sustain the field it has attained. It can't and while that field collapses, it generates a voltage in the opposite direction. It is a fast but pretty high voltage blip. That's called back EMF.
I measured in excess of -60V with just a scan tool that has limited bandwidth. The actual spike may be way higher than this. That's really not very good design; usually a coil has a reverse biased diode right across the coil to get rid of this sort of noise. It generates system noise but more importantly: it tends to take out the electronics that drive it or at least age it.
Subaru does not have these diodes in circuit. That's potentially wears the electronics down over time. Not sure whether this will happen in the lifetime of the car but it really isn't of sound design.
 

·
Registered
2018 Fozie XT
Joined
·
73 Posts
@Remco based on your knowledge, does it seems this design inherently causing more failure of the electrical part aka solenoid and valvebody. Also the heat issue expedite the wear/tear on the tranmission thus causing shorter life-span of the CVT.

It is definitely an interesting approach to transmission yet design and choices of materials seem to be a limiting factor.
 
21 - 40 of 66 Posts
Top