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. Any thoughts?
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.
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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).
Manual transmissions typically have recirculating fluid that's unfiltered. So the magnet keeps some of the shavings from recirculating.
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 miles.
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 effectiveness.
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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