Amsoil Differential and Transmission Oils Review
 

TLDR: Highly recommend Amsoil's 75w90 transmission oil over the OEM fill. Diff oil may affect the way the rear end behaves, which can be good or bad.

So I decided to change the differential and transmission oils in the FRS during spring maintenance. I know it really didn't NEED to be changed, but I wanted to see if there really was any benefit to an aftermarket fill vs the factory fill. I figured I'd go with amsoil, because why not? Skip to the bottom for initial impressions and follow up reviews after the change.

Note: My car has a Perrin shifter bushing and NA+tune power levels. No other current mods should really matter here.

Anyway, the change was super easy to do. Just needed a ratchet, 10mm hex head socket, and a mallet to break it free, plus whatever socket you need to pull the fiberglass underpanel (I forget, look it up :bonk:). The diff needs crush washers. You can reuse the transmission flat washers. Also, use a fluid pump of some sort if you haven't done this before, and remember to clean the drain plugs.

Found this to be a good how-to http://www.ft86club.com/forums/showthread.php?t=19218

Differential:
2qts or L of this:
https://www.amsoil.com/shop/by-produ...?code=SVGQT-EA

It looks like amsoil doesn't sell the oil with friction modifier pre mixed. I didn't get any friction modifier to mix in, just put oil in as it was. The factory fill didn't look to be in bad shape coming out. Definitely thinner than the amsoil, probably because the factory fill is 85 weight.

Transmission:
3qts or L of this:
https://www.amsoil.com/shop/by-produ...?code=MTGQT-EA

The factory fill was also not in bad shape here either. Both seemed to be about the same viscosity by my very unscientific measurements. Transmission actually took a bit more oil than expected before it came out the fill hole. About 2.6L judging by what I had left over.




Initial impressions:
I was only able to drive for a little bit and couldn't really push it. I'll update this periodically. Please note that I changed both oils at the same time, so there isn't ant driving with one or the other only.

Transmission Impressions: Wow. So smooth. I didn't know why people said the transmission felt crunchy until now, when it's no longer crunchy. For example, I used to tap the stick out of 3rd gear and it would land in neutral. Now, I tap the stick out of 3rd and it winds up in 4th. I was skeptical, but I'm a believer now.

Differential Impressions: It's definitely different, but I'm not sure it's any better. Doesn't drag the inside wheel around a (stopsigned) corner anymore so that's good. Around higher speed turns the car seemed different as well. Not sure if that's better or worse. I think I'm going to have to drive it a bit more to get a feel for it. Maybe I'll add some friction modifier and see what that does. I bought an extra liter so I can refill if I mess it up lol.

5/20/2018 Update: So I finally got to go for a good back road drive in decent weather for "evaluation" purposes. Conditions, 75F, sunny, humid AF.

Initial impressions on the transmission confirmed. The shifts were fantastic cold, but even better warm. I even entered first gear while moving with no issues. Rev matching that one is pretty tricky, but that's another topic lol.

I am not sure I like how the diff behaves now. It will still lock on tarmac, dirt, and the transition between (one wheel on each) but I think it's less progressive. This seems to make the rear less predictable and less stable at the limit. It seems like the throttle now has less of an effect on turn trajectory until closer to the absolute grip limit, and then all hell breaks loose (pun intended). I might be getting some friction modifier to try out.

1/10/2019 Update: Been driving with amsoil in the transmission and diff for a while now so this will be the long-term update unless things change.

I have been 100% satisfied with the transmission over the last few months. Still finding shifts to be excellent. For me this is a smooth throw with a crisp 'click' (technically a moment of resistance) when engaging the gear. This includes temperatures from 90F to 30F cold starts and warmed up. There is of course some extra resistance at the lower end of that bit I've found that I don't have to drive around (avoid) gear changes like I did with the oem fill.

I've actually been liking the differential fill more recently. Not sure if I'm getting used to it or something to do with temperature, or maybe my summer tires are dead and unpredictable. I've found the rear to be more predictable lately so maybe the oil wasn't the problem. I never wound up getting friction modifier.

I'll be interested to hear your comments about the Amsoil trans fluid in the winter. So far I've only used Toyota LV 75W (~50K miles), but if the Amsoil works in cold weather, it might be a candidate going forward.

Yeah, I'm planning to do a couple of follow ups.

Subbed for further review also. I'm not really impressed with redline fluids in this car so far and I have really liked amsoil in everything else I've used it in.

Yeah I was debating between redline and amsoil, but the BITOG forum folks seem to favor amsoil products.

yea but remember they also favor fram filters.

How is it possible someone prefers Amsoil and Fram filters?
I swapped out the factory fluids with Amsoil products when my FR-S was just a thousand miles old. I use an Eao filter and a Mag filter. No complaints at all.............but I run Amsoil in all my gear too, including all my yard equipment and 2 cycle fuels.

Really? That seems like an unusual pairing.

remember it is a forum and different people are in different parts. They have some weird people that want to spend as little as possible on oil and filters.

Updated initial post with 5/20 observations.

Interesting. I just picked up some amsoil for the transmission. Looking forward to trying it out.

Forgot to note that I have a Perrin rear shifter bushing (from well before the oil changes), but I expect my findings will still apply to stock. Added that info to the first post.

I finally put the Amsoil in the transmission. I can also verify that the shifting is much improved. Especially shifting in to second.

Hi Spuds,

Thanks for your very good review. I have issues with shifting quality of my 2017 BRZ. From searching the site, just like many owners experienced --crunchy and hard to shift into gears when cold. It even crunches when hot sometimes at low rpm crawling around town. I have these issues in every gear from first to sixth. The problems pretty much alleviates if I flock the car very hard and get it to high temp. When hot, shifting at high rpm (5,000 rpm and over) and my transmission shifts quite smoothly although it will not inspire a quick shifting action but the crunch is pretty much gone.

Did your transmission have these same problems before changing to the Amsoil?

If so, I really would like to give Amsoil a try on my car. I really hate crunchy transmission on my car. It just takes the joy out of driving. Wish I had a smooth transmission.

Thanks in advance for your reply

I have been told by my local 86 group and my STI friends to always go with Motul Gear 300. I want no part in a subjective debate, but just curious if I am missing something? Is Motul too expensive? Not good for our cars? I am about to change my fluids again after doing Motul in both Tranny and Diff about 30k miles ago and am open to suggestions if there is a different consensus on what is best for our cars.

Short answer, yes.

Long answer:
On reflection I do think my transmission could be described as crunchy entering every gear, particularly when cold. At the time, I just considered it normal, but I could see how someone could find it annoying. In my experience, amsoil fixed that. It's now smooth with an occasional crunchy shift when "cold", but that's just the nature of the transmission. I use quotes because I haven't driven it in under 70 F temperatures yet. Any winter driving may have a different set of issues.

Just to be clear, your transmission is not making grinding sounds right? I'm defining crunchy as it feels like you are crushing a bag of potato chips when entering a gear.

Your results may be a bit different of course, but it sounds like the amsoil MT oil will at least be a step in the right direction.

I was considering both motul and amsoil but it looks like overall preference on BITOG was amsoil. If you want to experiment, I say go for it. My motivation was just to see what would happen, and am happy with the results of the transmission oil change. Still need to try some of the friction modifier in the diff. IMO, the diff needs some friction modifier in the oil, and the amsoil doesn't come pre mixed.

Hi Spuds,

Thanks for your detailed answer. Appreciated it.

To answer your question, No I don't have any "grindings" in my transmission. It just feels crunchy going into gears. What I can describe is that I can feel I am moving a gear lever through something that is moving inside. Feels like dragging my stick through the gravels or something. It is not very obvious but it is kind of annoying. Moving the gear lever through the gate is quite sticky and heavy when the transmission is cold. It just make driving the car tiring and worrisome.

When cold (my cold means when I first drive the car after let it sit overnight as I live in hot climate morning temp is around 85 degree F) the problem will be worse as sometimes I can feel and even "hear" the crunch for the first few shifts but it will get better and better the longer I drive it. It gets best when I drive it really really hard like when I was running in the race track and that was when my transmission felt SWEET!!

How many miles did you have before changing the trans oil? Mine is currently at around 8,000 mile and still on factory fill.

Dragging a stick through gravel is actually a really good description. :thumbsup:

About 35,000 miles on factory fill before I changed it out.

The Motul is popular but the general consensus isn't always the best way to go. If you look enough there are quite a few complaints about Motul in these cars. No doubt it's good, but I believe most people in this thread are kind of experimenting to find what's best. Also, Amsoil is available locally for most people. That said, I would be interested to hear from anyone that has tried both Amsoil and Motul back to back.

Gear 300 is GL5 rated, which while acceptable in the 86's differential, it is not acceptable for the transmission. Other FWD Subaru's do require GL5 in their transaxles due to the incorporation of a differential (hypoid gears) into the unit, but our transmission does not have this.

That's not to say Gear 300 will immediately make your transmission explode. You could probably use olive oil for a while and get away with it. However, the additives which make the oil GL5 rated also have a detrimental long term effect on the yellow metals used in any transmission designed around GL3/4 oils, which includes ours.

Oh Hot Damn!! This just blew my mind with facts. :thanks:

Thank you!

Here's a nice read on the topic:

http://www.rtsauto.com/wp-content/up...nsaxle_oil.pdf

After putting about 1k miles on the car with amsoil in the transmission I will say that the second gear shift loves it. Second gear is almost always smooth at anything but the coolest temperatures. On the other hand, strangely, 5th gear seems to not like it as much. I have to shift to 5th more slowly now or it will grind when it never would before. Though, this could be a result of the transmission mount stiffening insert I installed at the same time. I'm sure the improvement in second gear is due to the amsoil though. In conclusion, I recommend it. I'll probably stick with it long term.

I'll pay attention to the higher gear shifts and report back.

Anecdotal chime in - my experience with Amsoil mirrors the OP. The gearbox shifts easier and smoother with their oil in it.

Drove it today, and 5th feels the same as other gears to me. I know that I had to get used to the shifter bushing when that went in and had to be more precise with the shifter. Agree with above assessment.

Some Amsoil MTG users experienced the same thing.

http://www.ft86club.com/forums/showthread.php?t=71030
http://www.ft86club.com/forums/showthread.php?t=118607

At what speed did you have the 5th gear grind?

@Spuds

Great review, I might have to try amsoil on my next MT fill (probably a couple years down the road. I am however concerned about your statements about what's going on in the differential, not sure if there's any real basis or fact in what you're saying about the different behavior so I'll have to take that with a grain of salt.

@venturaII indeed there is some concern about using a GL5 oil in the transmission, but I've read many times that Motul Gear 300 uses additives that reduce the negative effects on yellow metals. I've been using Motul for the last 3 years, had about 3-4 changes of it in the last 60,000 miles and it's been ok. The serviceable life of it for me is about 15,000 miles though and it does seem to degrade after that.

Those buffers work as a coating on the yellow metals to protect them from the corrosive action of the GL5 additives. However the coating will flake off the surface of the brass syncros every time they are engaged, which has a double negative impact of not only re-exposing the syncros to the corrosive ingredients, but also additionally by actually removing some of the substrate material itself (the brass) when the coating comes off. Differentials don't have this sort of inherent action, but synchronized transmissions do. Non-synchronized transmissions are another story entirely.

I suggest having an oil analysis done of your used GL5 transmission oil; I'll bet the yellow metal content will be high.

Thanks! As far as the diff, the worm gears will bind under certain torque conditions with little regard as to what lubricant is put in. I believe the friction modifier spreads that threshold out by creating a bit more resistance under load (meaning when there is a torque difference between wheels). The mechanical binding would still occur at approximately the same point, but the viscous forces would resist the torque difference between the wheels at a lower level of difference. This would explain what I am feeling in my subjective review.

One of my hypotheses in this little experiment was that friction modifier was not going to have any effect which is why I didn't buy any to begin with. I still have to see what adding some does to prove that right or wrong, but current observations seem to suggest that hypothesis was incorrect.

Well, just to add on to this thread, I just did another transmission lube change at ~54K miles. First was at 10K with warranty work; wrong lube was initially used and then dumped and replaced with the correct Toyota LV 75W fluid. Second change was by me at ~25K with the same Toyota fluid. This weekend I used Amsoil 75W-90 GL4 lube, and frankly, I don't like it. Noticeably notchier shifting, harder to get into first, even with double clutching on a slow roll. The transmission IS much quieter at idle in neutral though, which is interesting...

I'll probably give it 1000 miles; if things haven't improved, I'm dumping it and going back to the Toyota fluid, price be damned.

Any mount/shifter modifications? What is your local temperature? Mines still been good all summer, but maybe I'll run into notchy-ness too as things cool down? Trying to figure out how we had opposite experiences.

Less sound would indicate to me less energy loss, and therefore typically better lubrication. However, that might make the synchros slower to react leading to more notchy feeling. :iono:.

It's been around 60 degrees for the past week or so here in central New England. Shifter/transmission are 100% OEM, other than an aftermarket knob which has been on for ~6 months or so. The quieter operation I'm attributing to the slightly heavier 75W-90 Amsoil, versus the straight 75W Toyota fluid, though I could be wrong with that assumption. Might take a few hundred miles to break in to the different lube, so I'll be patient.. If the Amsoil is more 'slippery', that might account for the stiffer shifting/slower syncros, and maybe quieter running at the same time..?

I have about 30k miles on amsoil manual transmission & transaxle gear lube. I can usually get a smooth first shift of the day 1>2 if I shift at 3000 rpm. I don't drive the car in the winter but I usually get some temperatures in the low 40's before I put the car away. I think I do recall more effort going into first gear but I don't have any issues double clutching in the rare autox hairpin. I only seem to experience crunchy shifting if I'm short-shifting the car, less than 3000 rpm, or shifting slowly like in traffic. Otherwise it's fairly smooth.

I've noticed the same behavior when shortshifting 1-2 in cold weather, which seems like a natural thing to do until the motor warms up more. But holding 1st gear just a little bit longer before shifting does seem to help with the upshift, regardless of which fluid I've used.

I tend to be pretty easy on gearboxes and don't like a lot of effort required unless I know it's a beefy transmission, which ours has the reputation of NOT being.

There's definitely more resistance going 2>1 in normal driving then heel toeing into 2>1 at 5000 rpm during an autox.

I put 260k miles on a 2003 wrx 5 speed transmission, the last 90k miles were with an 18G and heavy duty clutch. I don't think these transmissions have the same glass transmission reputation?

I haven't heard about any reliability problems with 1-3 under any conditions. Usually the issues are with 4th right?

I got the impression our shift forks were also made of warm butter...maybe I'm wrong about that, but I consider the resistance to be excessive, especially compared to prior to the fluid swap.

37F on the car thermometer this morning, smooth 1-2 shifts this morning.