FL5 Transmission Fluid recommendation

[AspecR]

I would echo your experience on my Tacoma that calls for 75W-90 (Redline MT-90 is great, very slick shifting compared to the OEM fluid) however I'd note your location and put an asterisk on using MT-90 (instead of an oil with a viscosity closer to Honda MTL) in other parts of the country that get winter. @johnloov I don't know where you're at, but the Redline MT-90 75W-90 could cause issues in the winter that the Redline MTL 75W-80 you're looking at shouldn't cause.

I'm in South Florida winter isn't a concern

Sponsored

 

[Spart]

I'm in South Florida winter isn't a concern

Yes that's exactly what I'm saying, not sure if that is true for @johnloov who you were replying to though.

 

[Jester04]

I don't mean to single you out because I've seen plenty of people repeat this, however your post was first and shortest.

The owner's manual recommends "Honda MTF" which (see below) is equivalent to a 70W or 75W.

From page 805:

Our cars would be the ones "without auto idle stop" that require 2.32 quarts or 2.2 liters.

And from page 716:

Note on the left how it says that motor oil of 0W-20 or 5W-20 can be temporarily substituted? Well, 70 to 75W gear oil is equivalent-ish to 5W-20 motor oil.

Here are the kinematic viscosities (in centistokes/cSt or mm2/s) of Honda MTF and other 70W, 75W, 75W-80, 75W-85, and 75W-90 GL-4 MT gear oils:

Honda MTF (Approximately 70W but not listed as such)
7.265 cSt @ 100°C*
30.70 cSt @ 40°C

* Note that I found a VOA on BITOG from 2022 that measured the viscosity @ 100°C as being 6.96 cSt. Honda MTF has been through three formulations, so it's possible this number of 7.265 cSt @ 100°C is from an older formulation. Honda doesn't publish this data anywhere that I can find.

BG Syncro Shift II (75W-75 GL-4)
7.11 cSt @ 100°C
37.85 cSt @ 40°C

Castrol Syntrans FE 75W
6.3 cSt @ 100°C
32.2 cSt @ 40°C

Pentosin FFL-3 (BMW MTF-LT-5 equivalent)
7 cSt @ 100°C
34.7 cSt @ 40°C

Pentosin FFL-4 (75W-80 GL-4 and BMW MTF-LT-1/2 equivalent)
7 cSt @ 100°C
34.7 cSt @ 40°C

ACDelco Synchromesh 10-4014 (no weight specified, but close to 75W-80)
10.05 cSt @ 100°C
50 cSt @ 40°C

Motul Gear Power FE 75W
5.8 cSt @ 100°C
30.7 cSt @ 40°C

Motul Motylgear 75W-80
10.1 cSt @ 100°C
58.8 cSt @ 40°C

Motul Motylgear 75W-85
12.6 cSt @ 100°C
82.6 cSt @ 40°C

Motul Motylgear 75W-90
14.2 cSt @ 100°C
85.4 cSt @ 100°C

Redline MT-LV (70W/75W GL-4)
6.3 cSt @ 100°C
29.9 cSt @ 40°C

Redline MTL (75W-80 GL-4)
10.4 cSt @ 100°C
50.8 cSt @ 40°C

Redline MT-85 (75W-85 GL-4)
12 cSt @ 100°C
62 cSt @ 40°C

Redline MT-90 (75W-90 GL-4)
15.5 cSt @ 100°C
82 cSt @ 40°C

Royal Purple Synchromax
7.5 cSt @ 100°C
39 cSt @ 40°C

Amsoil "5W-30" Manual Synchromesh Transmission Fluid (note this is like a 75W-80 gear oil, no clue why they use the motor oil weight.)
10.1 cSt @ 100°C
49.4 cSt @ 40°C

Amsoil 75W-90 Manual Transmission & Transaxle Gear Lube
14.0 cSt @ 100°C
80.3 cSt @ 40°C

You will note that ALL of the 75W-90's in my list have significantly higher viscosity than Honda MTF, around double.

Honda MTF seems closest to Redline MT-LV, BG Syncro Shift II, Royal Purple Synchromax, Castrol Syntrans FE 75W, and Pentosin FFL-3/4. If those are called out as anything, it's 75W-75 and 70W/75W. Definitely not 75W-90 though.

Viscosity is not the only thing that matters for shift feel with a manual trans, though it can make a big difference in cold climates. Friction modifiers will alter the synchro feel, which is most of what you're feeling through the shifter. This is why what feels "right" in every gearbox will be subjective and oil from one brand won't feel the same as equivalent weight oil from another brand.

Climate and use also matters. If you live somewhere that doesn't really get winter, or you track your car, 75W-90 might be the ticket. But if you want like for like with OE, I would stick to 70W, 75W, or 75W-80 oils and pick your favorite based on friction modifiers (shift feel.)

For sure different options and people are free to choose their oil of preference.

I personally use the 75w-90

 

[Spart]

For sure different options and people are free to choose their oil of preference.

I personally use the 75w-90

I wasn't making a point about preference.

You specifically said "75w-90 is what it is supposed to use for gear oil on these cars" and that's completely and objectively wrong.

 

[Jester04]

I wasn't making a point about preference.

You specifically said "75w-90 is what it is supposed to use for gear oil on these cars" and that's completely and objectively wrong.

You are taking this so far out of context, reviving an old thread for what? I was answering a question from a person that wanted to change his oil to an aftermarket one. Which is a 90 weight oil that is recommended. Never claimed it was equal or the same weight as oem. Even with difference in viscosity it won’t break the car.

Really I don’t understand the point you are trying to make.

 

[gakhar]

Side point because I was wondering, what is genuine Honda MTF is graded to be? In my 08' Si I've always run AMSOIL 5W-30 MTF without issue. Is the AMSOIL bad for the FL5 because of the carbon coatings in the transmission?

I'm completely uneducated so just trying to learn.

 

[AZCWTypeR]

For some reason, gear oil and engine oil weight scales are different. 75W-90 gear oil viscosity is similar to 10W-30 engine oil. I've used Honda MTL, Amsoil MTL, and GM Syncromesh in other Honda's, though Honda's MTL was worse in sub-freezing weather for the 1st mile or so.

GL4 gear oils are kinder to bronze than GL5's, hence Toyota spec'd GL4 75W-90 transmission oil in my FR-S. I'm not sure about FL5's, but my old Porsche 911 had bronze shift forks.

 

[Spart]

Side point because I was wondering, what is genuine Honda MTF is graded to be? In my 08' Si I've always run AMSOIL 5W-30 MTF without issue. Is the AMSOIL bad for the FL5 because of the carbon coatings in the transmission?

I'm completely uneducated so just trying to learn.

Honda MTF is not labeled with a weight, and Amsoil's 5W-30 MTF bizarrely uses the wrong (motor oil) weight scale instead of the correct one (gear oil).

I don't blame you for being confused. You have to dig deep in the specs to figure out what is going on.

Honda MTF supposedly has these viscosity characteristics:
7.265 cSt @ 100°C
30.70 cSt @ 40°C

With cSt, a lower number means lower viscosity.

For comparison's sake, this is Redline MT-LV, which is billed as a 70W/75W GL-4:
6.3 cSt @ 100°C
29.9 cSt @ 40°C

By the book, 7.265 cSt @ 100°C lands in the 75 weight by SAE's numbers. However that applies to the last number you see if there are multiple numbers, with the first number applying to cold weather performance. 70W-75 and 75W should both be in the range of 6.5-8.4 cSt @ 100°C.

Many of the common replacements for Honda MTF are technically in the 80 range, i.e. a 70W-80, 75W-80, or a straight 80 weight. ACDelco Synchromesh, Redline MTL, and the Amsoil "5W-30" Manual Synchromesh all fall in the 8.5-10.9 cSt @ 100°C range.

As a general rule of thumb with most vehicle lubricants, it's never a good idea to go lower in viscosity than what the OEM fluid is. Going higher can be a good idea depending on your use case. For example, if you buy a GM V8 and they recommended that you run 0W-20 to save a few bucks on CAFE fines, it's a really good idea to run 0W-40 instead.

 

[Spart]

You are taking this so far out of context, reviving an old thread for what? I was answering a question from a person that wanted to change his oil to an aftermarket one. Which is a 90 weight oil that is recommended. Never claimed it was equal or the same weight as oem. Even with difference in viscosity it won’t break the car.

Really I don’t understand the point you are trying to make.

What context? You were the second post on the thread and answered OP's (very general) question with this:

75w-90 is what it is supposed to use for gear oil on these cars. The Amsoil MTF is not that weight but the gear oils do have options.

Your answer is wrong. 70W-75 or straight 75 weight is what is "supposed" to be used in these cars, per Honda's recommendation of Honda MTF, which performs in that range. 75W-90 oils have a kinematic viscosity of 13.5-18.4 cSt @ 100°C. That is fully DOUBLE the viscosity of Honda MTF, which is around 7 cSt @ 100°C. That's a BIG leap. That will cause shift performance problems for people trying to drive this car in frigid temps. That's not a good blanket recommendation to make, and frankly you should edit your post since it's the first answer in a thread that comes up in Google searches.

Really, I don't understand why you're trying to defend it. I started my post by explaining that I wasn't singling you out and I didn't want you to take it personally. I just wanted to correct an error I had seen repeated several times on this forum, not just by you but including by you.

 

[AZCWTypeR]

I've run well over 300k miles with AMS Oil MTF and Delco Syncromesh in three cars. No problems. Transmissions were still perfect at 200k miles (highest mileage of the three).

 

[gakhar]

Honda MTF is not labeled with a weight, and Amsoil's 5W-30 MTF bizarrely uses the wrong (motor oil) weight scale instead of the correct one (gear oil).

I don't blame you for being confused. You have to dig deep in the specs to figure out what is going on.

Honda MTF supposedly has these viscosity characteristics:
7.265 cSt @ 100°C
30.70 cSt @ 40°C

With cSt, a lower number means lower viscosity.

For comparison's sake, this is Redline MT-LV, which is billed as a 70W/75W GL-4:
6.3 cSt @ 100°C
29.9 cSt @ 40°C

By the book, 7.265 cSt @ 100°C lands in the 75 weight by SAE's numbers. However that applies to the last number you see if there are multiple numbers, with the first number applying to cold weather performance. 70W-75 and 75W should both be in the range of 6.5-8.4 cSt @ 100°C.

Many of the common replacements for Honda MTF are technically in the 80 range, i.e. a 70W-80, 75W-80, or a straight 80 weight. ACDelco Synchromesh, Redline MTL, and the Amsoil "5W-30" Manual Synchromesh all fall in the 8.5-10.9 cSt @ 100°C range.

As a general rule of thumb with most vehicle lubricants, it's never a good idea to go lower in viscosity than what the OEM fluid is. Going higher can be a good idea depending on your use case. For example, if you buy a GM V8 and they recommended that you run 0W-20 to save a few bucks on CAFE fines, it's a really good idea to run 0W-40 instead.

That explanation makes a lot of sense, thank you. By the wording in this thread I was initially under the impression that Honda MTF (and by result FL5 stock fluid) was 75w-90.

I have always run the AMSOIL MTF year round in my Si with no issues. In my FL5, do you think 75w-90 GL-4 from whichever brand of my choosing would be sufficient? Or do you deem it too viscous? What would be the draw backs?

 

[Jester04]

What context? You were the second post on the thread and answered OP's (very general) question with this:



Your answer is wrong. 70W-75 or straight 75 weight is what is "supposed" to be used in these cars, per Honda's recommendation of Honda MTF, which performs in that range. 75W-90 oils have a kinematic viscosity of 13.5-18.4 cSt @ 100°C. That is fully DOUBLE the viscosity of Honda MTF, which is around 7 cSt @ 100°C. That's a BIG leap. That will cause shift performance problems for people trying to drive this car in frigid temps. That's not a good blanket recommendation to make, and frankly you should edit your post since it's the first answer in a thread that comes up in Google searches.

Really, I don't understand why you're trying to defend it. I started my post by explaining that I wasn't singling you out and I didn't want you to take it personally. I just wanted to correct an error I had seen repeated several times on this forum, not just by you but including by you.

Whatever you say man! The OP never asked about manual recommended spec. So my general reply was as to look for a 75w-90 for an aftermarket fluid.

Again I never made a claim that it was what the manual recommended.

Could I have been more specific? Sure

Did I want to be? No, because it is a pointless debate and all these engine oil or transmission oil threads are simply silly, everybody has an opinion. And what is in the manual is not gospel, there are always acceptable ranges for these things.

I will not edit my post, common sense should be a thing and if people don’t have it then that is on them. If you live in colder weather use thinner oils, if it is hot you can bump up a bit without issues.

Still waiting on my other car’s trans and differential to blow up with the 75w-140 that I put on that is so out of spec.

 

[Spart]

So my general reply was as to look for a 75w-90 for an aftermarket fluid.

Again I never made a claim that it was what the manual recommended.

75w-90 is what it is supposed to use for gear oil on these cars.

Those two statements are completely at odds, and this is why your first response to this thread should be edited/corrected:

That explanation makes a lot of sense, thank you. By the wording in this thread I was initially under the impression that Honda MTF (and by result FL5 stock fluid) was 75w-90.

 

[Spart]

I have always run the AMSOIL MTF year round in my Si with no issues. In my FL5, do you think 75w-90 GL-4 from whichever brand of my choosing would be sufficient? Or do you deem it too viscous? What would be the draw backs?

It's hard to kill a gearbox with too thick of an oil. It's easy to kill a gearbox with the wrong additive package and wreck your synchros.

That said, our FK8/FL5/DE5 gearboxes have an internal oil pump so there's an additional failure mode: cavitation destroying the oil pump. Viscosity being too far out of range is one of the causes for cavitation.

Now I really doubt this is something you're likely to run into. You'd probably have to drive pretty abusively in cold weather without warming things up with a very thick oil. I haven't heard of anyone doing it, yet. But the potential does exist for someone to FAFO.

My two general recommendations are this:

• Shift feel in a manual trans has as much if not more to do with friction modifiers and the rest of the additive package than viscosity. This is going vary by manufacturer and individual product spec, not by viscosity range. The FM/add pack is why people love ACDelco Synchromesh, not because of the viscosity.
• Viscosity should be determined by your use case and ambient temps, and the manufacturer recommended viscosity generally caters to the lowest common denominator. If you live in Florida, you are never going to see a problem bumping from a 70/75 up to 80, 85, or 90 (talking about the second number here if there are two of them e.g. 75W-85 = 85). If you live in the midwest but you park the car in the winter, same story. If you drive in below freezing temps consistently, particularly temperatures around or below 0°F, you want to be very careful going too much higher in viscosity. If your car is a track build, you may use a viscosity that is utterly foreign for street use, for example Motul HD 85W-140 may be a really good fit for a track car and would increase the service interval between drain/flush. But not something I'd run on a daily driver.

 

[zumbooruk]

GL4 gear oils are kinder to bronze than GL5's, hence Toyota spec'd GL4 75W-90 transmission oil in my FR-S. I'm not sure about FL5's, but my old Porsche 911 had bronze shift forks.

My understanding is that GL5 will damage bronze parts

"Using GL5 gear oil, which is typically intended for differentials, could harm the transmission, especially if it has parts sensitive to the additives in GL5, such as synchronizers or other internal components."

Sponsored