My 2002 Subaru makes a higher pitched hum starting around 45 mph. When
checked I was told it had the wrong transmission fluid in it. I've been
driving it this way for about 6 months, 10,000 miles. Can a car run this
wrong with the wrong fluid? It's a manual transmission, no problems
shifting or starting and about 58,000 mi.
The dealer also said there were little metal pieces on the magnetic plug.
Specifics? Model and trim level would be a start although all
models probably spec the same fluids. I'm assuming you're in
the US since you used miles.
Subaru specifies an API GL5 spec gear oil in most countries.
The typical weight used is 75W90, suitable for a wide
temperature range. A mistake would have been using motor oil
or automatic transmission fluid. Some manual transmission
actually use these fluids. If the proper fluid has been
used, nearly all of the improper fluid should be gone.
Like I said, some older manual transmissions (Honda and Saab
come to mind) used motor oil. The key was that the older
motor oil formulations had certain ingredients that worked
OK. Newer API requirements reduced the level of certain
antiwear agents that did OK in manual transmissions. Honda
now specs a proprietary fluid that seems to be gear oil.
The problem with motor oil or ATF would be the viscosity
and extreme pressure protection. I wouldn't be that
concerned for that short a period of time. Any longer, and
the antiwear agents might degrade.
The car is a Subaru Forester, 4 dr wagon. The dealership where I purchased
my used Subaru, thought the car wouldn't have made it nearly as far with
the wrong transmission fluid.
I'm wondering if the transmission is going out or maybe there's a
completely different problem.
Finding metal on the magnetic plug is _never_ a good sign. That,
coupled with the fact that it is making unusual noise, would seem to
indicate something bad in the tranny . . .
Running the car with the transmission dry would certainly cause rapid
failure, but having motor oil, or even ATF in it _probably_ wouldn't
hurt anything over the short term.
I'd switch to a good synthetic (we've had good results with the Amsoil
products; Redline is good as well), and see if that doesn't help.
Also, when you drain the fluid (this should have done this right off;
I question your mechanics competency) look for suspended metal flakes
(looks kinda like metal-flake paint) in it. This is a sure sign that
the transmission is on it's way out.
You're probably outside of the warranty, but it might be worth
checking. Otherwise, just keep on driving; typically a tranny will
give plenty of warning before failing totally; a synthetic fluid may
extend the transmissions life indefinitely. Or not, but if not you're
probably looking at $1500 or more to replace it, so it's probably
worth the $35 or so cost of the synthetic fluid to try.
FWIW, ~3 quarts will refill the transmission if all you do is open the
drain plug; you pretty much have to hang the tranny tail down for
awhile to get all of the fluid out.
Steve Jernigan KG0MB
University of Colorado
It's actually normal to find some metallic particles on the drain
plug. The reason the magnet is there is to catch the fine pieces that
are the result of normal gear wear inside the transmission, so those
bits don't continue to circulate in the oil. So if there is a light
coating of what looks like tiny metal filings or shavings on the
magnet, that is not a cause for concern. However if there are any
larger pieces that is another story. Obviously a chunk or gear tooth
stuck on there is bad. It's up to whoever is doing the drain/fill to
evaluate what is seen. Unfortunately some shops will take advantage of
an owner who doesn't understand the above, and show them the plug with
metal shavings on it as an indication that their transmission needs
major repairs (read $ for the shop).
In my opinion mulder is quite correct in that metallic fuzz is normal
but, not chunks. Instead of all this conjecture why the bleep not just
change to a brand name 80/90 GL5 gear oil and be done with guessing?
You keep screwing around looking for possibilities and guessing so
just do it in case your continued driving will wreck it more.
Manual transmissions typically have recirculating fluid that's
unfiltered. So the magnet keeps some of the shavings from
The main problem with using the wrong fluid would be long-
term gear protection or premature synchronizer wear. You
might get OK protection for a few thousand miles until the
antiwear additives break down. A 10W-30 motor oil is similar
in viscosity to a 75W-80 gear oil. Motor oil might also be
too slippery for the synchros.
Gear oils use extreme pressure additives. They're great in
that environment but lousy in manual trannies. Motor oils
use antiwear additives. They're fine in the engine but don't
last when sheared by gear teeth. Older motor oil formulas
contained higher levels of ZDDP antiwear additives; Honda
said it was OK for up to 30K miles.
I'm personally using Motul Gear 300 75W90 in my 2004 WRX.
It's a bit pricey, but I'm going to change it every 30K
Clarification - that should read, they (EP additives) are great
in manual transmissions, but lousy in engine oil. EP additives
do well in a more or less sealed environment like the tranny.
Some motor oil makers have been accused of using EP
additives to boost the performance of their oils in bench
tests. Then all the combustion byproducts in a real engine
will supposedly cause the EP additives to lose their
Update - the transmission fluid has been drained & replaced. I talked to
Subaru who suggested having the car re-looked at to make sure it wasn't
anything else. Esp. since some filings are normal to appear on the plug.
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