Transmission/Differential fluid change interval? - Subaru Forester Owners Forum
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post #1 of 6 (permalink) Old 10-22-2007, 12:30 PM Thread Starter
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Transmission/Differential fluid change interval?

I have searched and have not been able to find a specific discussion re: the "official" Subaru replacement interval for the transmission and front and rear differential lubricants.

The Subaru Official Maintenance Schedule (US)
Subaru Maintenance Schedule (US)
simply states "I" (Inspect) every 30Mo/30k miles under the normal service schedule. With no required replacement listed at all.

The only explanation I was able to find was in this thread;
15k service

Quote:
Originally Posted by sa_lontoc View Post
From EndWrench (Subaru Maintenance Schedule) :::

There is no recommended replacement interval for the transmission fluid on
late model Subaru vehicles. The same applies to manual transmission and front
and rear differential lubricants. In all cases, the recommended procedure is a
fluid inspection at 30 month or 30,000 mile intervals. If the fluid in any of these
units is found to be dirty, contaminated or at the incorrect level during the
inspection, fluid replacement and/or seal or gasket repair are the only options.
Differential and transmission fluid recommendations for varying climate
conditions can be found in the appropriate Subaru service manual. Subaru recommends
against the practice of mixing lubricants from different manufacturers.
Although both may comply with the GL and API ratings, lubricants from differ-
ent manufacturers are refined from different base oils and additives. Combining
them may produce unpredictable results.
Rear differentials and manual transmissions feature familiar add and drain
plugs, while many Subaru automatic transmissions actually have a drain plug
in the transmission pan (a feature welcomed by anyone who’s ever had the
misfortune to take an ATF bath). Another welcome feature is the fill level
dipstick that can be found on manual as well as automatic Subaru transaxles.
AFAIK, this is not covered in the standard owners manual. I find it hard to believe that Subaru would leave open the possibility that a vehicle could go up to 120k without changing the tranny/diff fluids depending solely on a couple of "inspections" over the life of the vehicle performed by service mechanics of widely varying expertise and experience.

Do most owners simply skip the inspection and perform a fluid replacement every 30K (15k Severe), especially since only a portion of the fluid is actually replaced each time?

(And what's up with SOA leaving this big gray area, especially in light of the tightening of oil/filter change interval for '08)
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post #2 of 6 (permalink) Old 10-22-2007, 01:17 PM
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Just replace it at 30K. It's cheap and diffs and trannys are not.

'09 STI
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post #3 of 6 (permalink) Old 10-22-2007, 03:24 PM
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Quote:
Originally Posted by donsev View Post
(And what's up with SOA leaving this big gray area, especially in light of the tightening of oil/filter change interval for '08)
I can't answer for Subaru of course, but only the engine oil is subject to combustion byproducts, unburned fuel (while warming up) and any possible coolant leakage, and also the greatest heat (the underside of the piston crowns and the exhaust valve stems). It's the most hostile environment for oil, which is why it has the shortest change intervals, even before the 2008 turbo schedule changes.

07 Forester Sports XT 4EAT & 02 WRX wagon 5MT
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post #4 of 6 (permalink) Old 10-23-2007, 11:50 AM Thread Starter
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Quote:
Originally Posted by Graham View Post
I can't answer for Subaru of course, but only the engine oil is subject to combustion byproducts, unburned fuel (while warming up) and any possible coolant leakage, and also the greatest heat (the underside of the piston crowns and the exhaust valve stems). It's the most hostile environment for oil, which is why it has the shortest change intervals, even before the 2008 turbo schedule changes.
Sorry, my intent was not to compare the fluid change interval requirements of the tranny/diffs to engine oil, but to point out that SOA has at one extreme; a theoretically "indefinite" interval requirement for tranny/diffs, and a rather short 3.7K mile required interval for turbo engine oil (both compared to industry standards).

I do not know of any other manufacturer that does not list a discrete tranny/diff fluid change interval for normal service (be it 15k, 30k, or 60k). Which, as I understand it, could allow an owner, while following all guidelines, and even having his services performed at a Subaru dealership, to never having the fluid replaced in his transmission - based solely on the judgment of the random service mechanic assigned to the couple of inspections throughout a 120k mile life.

I just find it odd that SOA would allow a situation where someone could a) have their car in for 60k service (all services performed to date but no tranny fluid yet changed) b) get a mechanic who happened to have a cold, so he didn't notice the burnt aroma of the tranny fluid, and then c) suffer tranny failure at 70k miles - just out of the powertrain warranty.

The owner did everything right, yet he has little recourse for his failed transmission
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post #5 of 6 (permalink) Old 10-26-2007, 04:59 AM
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Quote:
Originally Posted by The Black Box View Post
Just replace it at 30K. It's cheap and diffs and trannys are not.
Agreed.....I change the tranny & diff fluids every 2 years or 30k miles too.

Bren

Proud owners of a 03 XS & 2005 Lexus ES330
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post #6 of 6 (permalink) Old 10-26-2007, 09:53 AM
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i will do 30k changes for our 07 fxt

i've been doing 30k changes on my 02wrx....
(it's been good for my for 150k miles so far)

dm
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