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Change To Syn Gear Oil Now!

73K views 268 replies 95 participants last post by  markthomas1969 
#1 ·
Lots of people mention the subject, but maybe it needs it's own thread.

Change your gear oil to synthetic as soon as you can. I used Mobil 1. One gentleman (he inspired me) used Redline. It might be better but its hard to find, here.

Keep the car level (no ramps, you can reach the drain) and drain every drop of the old oil. Mine only has a few K miles on it. Since my car is lowered, I needed my skinny son to get at the drain plug. Don't lose the washer!

You'll need a long a$$ funnel. Then dump in that Mobil 1.

I think the owners' manual is wrong in the capacity. It calls for 3.75 quarts. I used 4.

Then go for a drive and be prepared for a seriously dramatic change in your shifting and transmission behavior. It's hard to believe it's the same machine.

Go figure.

:) :)
 
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#227 · (Edited)
I've got a quick question. I am not sure what sort of manual transmission fluid I have in my car, but it does seem to be a bit low. Could I just put in some 75W90 oil to get it to the right amount, or should I add some synthetic to it? Is it bad to mix the possible "dino" oil already in there with some synthetic, if not could I use dino oil?. I do not want to do a full drain and refill with a full synthetic fluid. If I should just add regular dino fluid, what is a good kind and I also wonder the same for the synthetic. Thanks in advance.

*EDIT*
By the way, my transmission is working smoothly with no grinding or syncro problems, another reason I am skeptical of switching to synthetic. I mainly just want to get the fluid level where it should be and not have to worry about any issues. Thanks again. :)
 
#228 ·
The fluid level is hard to read and not consistent between reads depending on temp and incline or just plain luck as far as I can tell. On an 05, you probably have less than 30K? So you've got the factory fill in there still? It's unlikely you're low without a problem, and it's unlikely you've got a problem. Are you sure it's low?
 
#229 ·
I have a little under 20,000 miles on the car and I acquired it in April with 17,500 on it, so I have no knowledge of what's in there. I have tried checking the fluid various ways, including just cold, driving for a while and let it cool for 10-15 minutes and check, checking right after driving with engine off, right after driving with engine running, and all of the times on nearly level ground. When I checked it all of these different ways, the closest reading I can get to the low marking hole still leaves the fluid a good 1/8" from the indicator. What do you consider to be the best way to check it? Also thanks for taking the time to help me, I've been watching these forums for a while and reading, even when I didn't have a membership or a Subaru for that matter, and I was always amazed at your knowledge of these cars.
 
#230 ·
Anything should be compatable, dino or synth for a band aid repair. Just make sure you do a full change on the fluid within the next OCI and you should be ok.


First you need a fresh chicken, some rosemary, garlic, 1/4tsp salt and ..oh wait...thats another set of instructions....


What you have to do is heat up the trans by driving the car. (couple of miles, reach hwy speed)
Park on a level surface.
Car off or on doesnt seem to make a real difference, but I turn mine off....
Check the fluid at least 2 times.
Adjust accordingly.

I judge my level surface by the orientation of a glass of water in the cup holder (which might be slightly off but seems to work well).... sometimes I only change it when there is a planetary alignment....just to make sure.

Under heat, the oil is coating the gears and heat is expanding the fluid. It doesnt take much of this to make a difference. This is why you check trans fluid under operating conditions....to make sure you have enough in the splash case when the car is actually being driven.
 
#231 ·
2005BlackWRX said:
I have a little under 20,000 miles on the car and I acquired it in April with 17,500 on it, so I have no knowledge of what's in there... What do you consider to be the best way to check it?... I was always amazed at your knowledge of these cars.
I'm all smoke and mirrors, don't fall for it... I overfilled mine when swapping the fluid! What I now aim for is the fluid reaching the L mark or just above when cold; when warm, that means halfway between the two marks. If you're concerned you can add a little from the top (just a little, it's easy to overshoot). Just use a long funnel and add a teaspoon at a time.
 
#234 ·
#235 ·
#236 ·
****, they were right, impossible to find. I had to order one from some tool place i found through google... now i have to wait for slow ground shipping.:unhappy:
 
#238 ·
Ya, i got it for like $14 shipped. At least i don't have to go running around looking for a plug from a bugeye. I'd probably pay the same for the plug through Subaru as i did for the Torx bit.
 
#239 ·
Well, i got the torx today and changed the tranny/diff oil and let me tell you... it's night and day. Redline MT 90 is awesome. I'll never go back.
 
#240 · (Edited)
Replaced the tranny with Penzoil Synchromesh (only because I couldn't get ahold of Amsoil MTG.)
Replaced rear diff with Subaru LSD.

I tried to get the Subaru Extra S, but they didn't have any. The parts guy hadn't even heard of it. The dealership mechanic essentially said the Subaru LSD was overkill. Pleasant experience with these guys.

Previously I had Amsoil Series 2000 75W90 in both. Got almost 70,000 miles out of them (don't flame me.) No problems till just recently and I'm completely happy with it. There were some minor metal particals on the tranny bolt, but less than the original fluid swap at 30,000 miles. I got no metal particals out of the rear diff. They don't make the series 2000 anymore though. I'll swap back to Amsoil for the low temperature properties when I get back to Alaska. :)
 
#244 ·
Damon_Chambers said:
i changed out the rear diff. fluid the other day but i didnt use a torx... i just used the "socket" end of a socket wrench that fit in the hole. it fit perfect and didnt slip at all.

ill be doing the tranny fluid probably next weekend. does the tranny use the same plug as the rear diff?
No.

The rear diff fluid that you just changed takes a 1/2" square wrench, or, as you found out, the end of a 1/2" drive socket wrench.

However, the tranny will take the T70 bit. I don't think there's any way around it.
 
#245 ·
wow

This is the longest thread I've ever commited to reading. As expected from something with so much input, there is no clear winner at the end. After all of that information I'm still damn confused. I really like what people have been saying about Syncromesh, but as it is GL4, many people are saying it will reduce the life of my components. The reason I want to switch fluids are: I love my car (05, 10k miles) but it could definitely shift smoother. I hate my 1-2 shift and getting into 1st from a roll is a battle. If switching fluids could fix this (and quiet down the tranny and increase gas mileage at the same time) I'm all for it. However, I live in Vermont so it has to run well in the cold (-20 F). Running 100% Syncromesh sounds like it could have negative long term effects, but running 100% Redline sounds like it doesn't perform with the buttery smoothness of the GM stuff. Would a 50/50 mix of the two give me the best of both worlds? Any input would be greatly appreciated. If any of the guys who were using Syncromesh way back when would like to chime in to report their long term findings, that would be great. Thanks.
 
#246 ·
I read this entire thread and its crazy, my question is, when looking into fluid some of them say GL4 and GL5, does that mean its good for both, for example here http://www.pdm-racing.com/products/motuloil.html they sell motul and they have the synthetic blend and the pure synthetic and it says "API GL4 and GL5 MIL-L2105C" so I am assuming that its good for both and would work without causing damage to the subie gearbox correct?
 
#247 ·
correct. For on street driving GL4 or GL5 will suffice, with minimal if any damage to front diff.
The reason we need the GL5 spec is for the open diff in the front that shares the same fluid as the tranny.
I have noticed that the car shifts much better in the winter with a 50/50 mixture of the RedLine GL4 MT90 and 75w90 NS GL5 spec fluid. If i lived in Florida or the like, than a full tranny of the 75w90 would work just great and satisfy all the Subura specs. But given that every once in a while the temp drops into the teens or less in NJ/NY, the 50/50 mixture significantly helps shifting ease before everything starts warming up.

It's a catch 22 situation, go with the straight GL5 thick stuff in cold climate and the synchros take a beating, go with some GL4 fluid and help the syncros but possibly harm the ring and pinion up front when very hot and beating on the car.
 
#248 ·
if thats the case then something that satisfys specifications for both gl4 and gl5 would be the best bet right? since its formulated for both i would think it would be a compromise of both properties, and the Motul motylgear is a synthetic blend which i guess would also be a happy medium since throughout many people said not to use straight synthetic either
 
#249 ·
ok, so i read about 10 pages, and didnt find the ULTIMATE answer, yes or no to synthetic oil?

changing it tommorow...so if anyone has an answer, that would be sweet...

however im getting the idea that weather or not to use syn is situational...in that case maybe ill just ask around? i dont use my car on a track...so yeah...
 
#252 ·
can those that used snychromesh comment? or those with shockproof comment about longevity? I have Royal Purple 75-90w in mine and have difficulty getting into first in the morning... I'm considering draining some and adding a quart of snychromesh and see if that helps. I have ~ 111,000 miles on my rex and looking for a better driving experience with longevity.

Thanks.
 
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