My '08 shifts almost too smoothly and quickly - I know that sounds bogus, but I was considering adding a little Mobil1 75W-150 to the mix to get it to feel, in "goldilocks and the three bears" terms, "just right" but thought I'd call Honda Technical Service Line first. They are as secretive as the rest of the free world as to the viscosity of Honda MTF but did admit that the viscosity is measured differently than in motor oil terms, ultimately leaving me with the impression that it is a 75W-90 gear lube. They also said that Honda has reformulated their MTF into a truly wonderful lubricant, which I saw on other forums also, and recommended that I try it first - it is P/N 08798-9031 with a green label, white letters and white cap (he emphasized the white cap). My local Honda dealer doesn't have any, all they have is a red cap bottle which is apparently the old stuff, and they actually seem somewhat mystified as to what lubricants they actually carry for which transmission. So, I have two questions:
1) Do you know if my '08 Fit came with the old MTF or the new MTF, and
2) Is there a good source for Honda lubricants if my dealer seems unable to figure out how to get the new stuff?

 

Everything I've read suggests that Honda MTF is around 11.5 cSt @ 100C (corrected 4:24PM PST), which would make it a somewhat heavy 30wt, almost a light 40wt.

The problem with gear oil (like 75W-150) is that the additive package may be corrosive to the yellow metals found in manual transmission synchros.

As for your shift feel, I'm not sure that you're ever going to get a cable-actuated gearbox to feel like a directly shifted rear-wheel drive unit. From reading your post, it almost seems that this is what you're looking for.

 

I just noticed that you're in Fairbanks. You might want to consider switching to a lighter winter fluid when appropriate. Amsoil MTF or Redline MTL might offer easier cold shifting.

 

The stuff I get from the local Honda dealer is normal engine oil 15-40 in Honda plastic bottles. On my 4th change and it works fine because it's so hot here. In Alaska you might be better off with 10-30 in the cold.

 

Thanks, guys. I did find that the reformulated MTF was first used as factory fill on M/Y 2007 Fits. My winter shift performance is excellent; the issue is that it feels even too slick. I had a 1984 Suburu that I added Mobil1 75W-140 to the transmission and it made it feel just right, so I know it is possible to tweak synchro performance with viscosity for a certain feel. Richard, that is new info regarding yellow metal; do you know if it matters that I would be using a synthetic oil (Mobil1) and is it the same issue for 75W-90 as it would be for 75W-140 then? Can you share more info regarding the corrosion issue? Thanks!!

 

There's info scattered around the web regarding GL-5 gear lubes and their sulfur-based extreme pressure additives attacking brass, bronze, and copper. I don't know how reliable that information is, though.

You can get 75W-90 gearbox lubes if you really want to try something heavier. Both Amsoil and Redline make ~15cSt fluids that might work well. Those are about the heaviest manual transmission specific lubes that I know of. If you really need to go heavier, you might blend-in some 20W-50 or something (around 18cSt @ 100C).

You might consider a 15W-40 as a demo just to see how the box will react to a 15cSt fluid without having to place a special order and spend a lot of cash. I put Rotella T synthetic 5W-40 in a Daimler NSG370 box as a test and I liked it so much that I kept it in there.

 

Richard,
I think I'll do a query on Rennlist as I used to have a '87 Porsche 911 Carrera. The most popular lubes for the G50 Carrera transaxle were Mobil1 75W-90 or Redline. I personally do not like Amsoil lubricants after personal comparisons to Mobil1 in hydraulic lifters in my Jeep Cherokee. On the Mobil1 75W-140 label it says "Outstanding protection for hybrid differentials where an API GL-5 quality 75W-140 oil is recommended" and also "Gear shifting ease and reduction of chatter." I really don't know what I'm doing in the strictest sense; I would prefer to use at least 50% Honda reformulated MTF in order to retain their additive advantages; perhaps 50% Mobil1 75W-90 would be a better choice than 75W-140.

 

I guess the answer was here: Will Sulfur in Gear Oil Harm Manual Transmission Synchronizers
all along. I must say that the archive list on the left of the web page covers every conceivable oil question I could ever ask! Thanks again, Richard. In the Mobil1 archives there's aven an entry regarding Mobil's answer to the Amsoil test comparison.