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Tranny fluid overheating... ???


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14 replies to this topic

#1 anddor5

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Posted 18 July 2010 - 12:53 AM

Hello everyone. I'm new to this site.

I have a 1998 Legacy Outback, 30th anniv. Owned it for over 7 yrs, and it's been a great car - Love it!

It has a problem: Tranny shows signs of torque bind in AWD mode on tight turns at slow speeds. Putting fuse in FWD slot disables the Rear differential and problem goes away... temporarily. If I drive the car long enough (about 40-50 min) in FWD mode the car goes in AWD mode by itself. FWD light disappears from dashboard and torque bind comes back. In addition, when I put it in Park in this state, and turn off the ignition, the car makes a single jerk. When it sits for a while, cools off, and I start it, the "At Oil Temp" light flashes 16 times, then stops. Car goes into FWD mode again, drives fine until I drive it long enough to "overheat".
So here are my questions: Is it tranny fluid overheating that causes it to override FWD mode by itself? What causes fluid to overheat? Can malfunctioning fluid temp sensor cause this? Is this an overheating issue at all? Please, any suggestions, thoughts, ideas - anything guys. Please, help.

#2 grossgary

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Posted 18 July 2010 - 02:19 AM

you'll see "T" in a lot of equations because conductivity is related to temperature. electromagnetism discussions aside, electrical problems are often heat related, that's well known in any electro-mechanical biz. doesn't have to be "overheating", it's just probably sensitive to temp's now that it's on the verge of failing.

my guess is you need a Duty C solenoid replaced. it would be nice to pull the actual code, which is a convoluted process detailed in other threads on this site.

has the fluid ever been changed? has the trans filter ever been changed (trans filters started in 98 or 99)?
do the tires all match?
how many miles?

binding does bad things to other components, but you probably know that.

#3 anddor5

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Posted 18 July 2010 - 01:20 PM

Thanks for reply, Grossgary.
Yes, when it started showing these symptoms, I changed fluid immediately, but not the filter. (actually, this happened 3 yrs ago, and changing fluid fixed the issue.) The old fluid was clean, but I replaced anyway, and added 1.5 bottles of Lucas Transmission Fix (like last time). Issue seemed to go away for 3 days, but came back. Tires are pretty new, replaced them all just under a year... but i'll check into that anyway. Car has 117k
I never replaced the filter - i was told that it really doesn't need to be... does it make the difference? Also, car drives pretty fine in AWD for a little bit, while its still not too hot. Since this issue started, I've noticed that even in FWD mode it shifts a little harder than it did before... is that an indicator that entire tranny getting ready to go?

#4 grossgary

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Posted 18 July 2010 - 01:32 PM

these are classic symptoms of torque bind, very common. torque bind that doesn't go away with the FWD fuse is 99% of the time the Duty C needs replaced. one good thing is that it's not terribly horrendous of a job and can be done yourself without removing the transmission, lots of information about it on here.

if you're not convinced or want more diagnosis your next step is to read the code(s). search for info here on doing it yourself or have a dealer/shop do it.

the Lucas treatment is not helping anything. additives like that are short term band aids for symptoms that cause long term issues. there's one trans additive often recommended for subaru's, but that's for an entirely different issue and product and is limited to 99 and 2000 model years. a Subaru trans that doesn't operate properly on ATF has something wrong with it.

it is a filter and it's 13 years old, i'd replace it but i doubt that will fix your issues.

the hard shifting would make me wonder too, but if it's shifting fine during warm up while the AWD is working i wouldnt' worry about it. is that the case?

#5 anddor5

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Posted 18 July 2010 - 02:09 PM

I just tested it again to make sure:
Car is completely cold. I put it in AWD mode and drove for about 10 min. Did several tight circles on a slow speeds, did a little bit of accelerations - shifts OK, no torque bind whatsoever. So, this confirms again - only happens when it heats up a good bit. Can heat sensor be at fault?
I will look into solenoid replacement. Is there any documentation on how to do it? talking about visual aid :)

#6 grossgary

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Posted 18 July 2010 - 02:41 PM

sounds like Duty C. lots of threads on here and pictures of it and such. i'd play with that search feature above it's extremely helpful and will prove valuable. never heard of one so consistently doing that cold/warm thing before but i'm not terribly surprised either. maybe someone else will chime in?

#7 anddor5

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Posted 18 July 2010 - 03:29 PM

sure. I'll keep digging. I greatly appreciate ur tips. Thanks!!

#8 nipper

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Posted 18 July 2010 - 07:38 PM

THE ATF light on means there was a electrical failure on the last drive cycle.

Does it flash on startup?

On a 1998 it can be a bad Duty C, or a sticking pressure valve, or a sticking Duty C.

Do all the tires match and are of equal wear?

On a sooby this old, instead of just replacing the C, i would also put new clutches in the AWD unit, do right do it once never go back. Do it 1/2 way Mr Murphy will knock on your door.

I would NOT touch the filter. It is ony a screen. Most people mess i up removing the pan and make a leak that is tough to resolve.

#9 anddor5

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Posted 20 July 2010 - 04:26 PM

Yes ATF light flashes, and it is correct - it only happens when it does overheat. When car is cooled off, and I drive it for short time and being pretty easy on it, it doesn't overheat, so next time I start it - the light doesn't flash.
All tires match, all bought at the same time about a year ago, and were rotated regurarly, in cris-cross pattern. Haven't touched the filter, not planning any time soon, unless really have to.
Also, Mr. Nipper: how hard is replacing clutches in AWD unit? can it be done outside of the shop? is that pricey? any way to way to fix sticky valve and sticky Duty C without replacement? like cleaning, etc?

#10 nipper

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Posted 20 July 2010 - 05:18 PM

This has NOTHING to do with overheating, period.

As I said before, the 16 blinks indicates that there was an electrical fault the last time the car was operated. If the cars trnsmission was overheating the light would come on when hott, and go off when cool, and that would be it.

at 13 years old the AWD units do get tired. You can do this in your driveway if you want, there is a lot of information here on the process. Skipping the clutch replacement is like just chainging only the timing belt. It will work but eventually you will be doing the job all over again.

#11 anddor5

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Posted 20 July 2010 - 07:48 PM

Ok, I don't mean to be stubborn, but if not overheating, then why does it happen only after prolonged drive? If I drive it short and sweet - it never has any issues. Thanks for your time!

sorry, i'm new to this message board, as u can see technical issues :S

Edited by anddor5, 20 July 2010 - 07:54 PM.


#12 anddor5

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Posted 20 July 2010 - 07:51 PM

Ok, I don't mean to be stubborn, but if not overheating, then why does it happen only after prolonged drive? If I drive it short and sweet - it never has any issues. Thanks for your time!

sorry, i'm new to this message board, as u can see technical issues :S

#13 grossgary

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Posted 21 July 2010 - 04:18 PM

Ok, I don't mean to be stubborn, but if not overheating, then why does it happen only after prolonged drive?

if you're not convinced or want more diagnosis your next step is to read the code(s). search for info here on doing it yourself or have a dealer/shop do it.

the TCU knows the circuit that is causing the issue, so read the code is your next step if you don't trust the info you're getting here. in my opinion there's no value in discussing the 0.01% other possibilities that could cause your issues. i've never heard of anything but Duty C's causing the issues you describe, though i agree it's interesting how repeatable it seems to be. but i'm not that deterred by it either, like i said electricity and temperature are highly correlated.

how hard is replacing clutches in AWD unit? can it be done outside of the shop? is that pricey?

Duty C is probably failing, not clutches.

the Duty C needs replaced. one good thing is that it's not terribly horrendous of a job and can be done yourself without removing the transmission, lots of information about it on here.

you would need to let us know what kind of work you're comfortable doing for us to offer more

roughly $500 at a dealer (parts included in that price), less at an independent. i just posted a couple months ago what my friend paid, he supplied the parts to the dealer in Atlanta, find that thread for a number as i don't recall.

any way to way to fix sticky valve and sticky Duty C without replacement? like cleaning, etc?

No, you replace the solenoid. i've "fixed" other solenoids but i wouldn't do it in this case, but that's just up to you. i've never heard of anyone doing it on these. new is a much better solution for most people, the minor cost isn't worth the time and risk for most folks.

#14 nipper

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Posted 21 July 2010 - 05:40 PM

The car does not do it cold because the fluid is thicker when cold. As it heats up it gets thinner and looses pressure. Also as the coil for the solenoid heats up, resistance increases in the solenoid. If the coil is weak it will start to fail.


Simple electric theory. As temp increases so does resistance. Add that to thinner oil you have an unresponsive circuit.

#15 anddor5

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Posted 22 July 2010 - 03:50 PM

Thank you both, guys! This clears up all my questions at this point. I'll start on working with codes first, and will take it from there. Thanks again!!!




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