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