1995 Civic Ex transmission oil
 

Has anyone had success using 5w20 or 0w20 or something lighter than recommended fluid in a manual Honda transmission? I sometimes have trouble shifting and am thinking I need to check or change the fluid. I just got the car so don’t know when it was last changed.

Has anyone used something super light in a 90s Honda transmission?

To my knowledge, 0w20 only comes in synthetic, and that'll cause hard shifts. Synthetic is too slick and prevents the syncros from grabbing and synchronizing the gears.

To my eye, Honda's current MTF formulation is a lot thinner than 10w30, and it works well with syncros. I recently refilled Aerocivic with it and it shifts like butter.

Honda MTF is good. It's a pretty light fluid. Any ATF is probably OK too. Some people like Pennzoil Synchromesh. I haven't noticed much difference between fluids in Honda manual transmissions. I wouldn't use motor oil unless I absolutely had to. I tried straight 30w once. It made the synchros pretty slow when cold!

My recommendation is always use the oil stipulated in the owner's manual. Transmissions don't have the same circumstances as an engine. The different types of metal, the way they rub together, the pressure, the lack of exhaust gases, dust that makes its way past the air filter and gasoline contaminating the oil, not having a heat source in the same block; all this is different in a transmission.

Synchros do eventually wear out, but so does oil. If you do use a lighter oil, use one that's close to the oil specified in the manual and maybe learn to double clutch.

I'm pretty sure that Honda recommends using 10w30 motor oil in their transmissions from the 90s, if you don't have Honda MTF. I'll have to double check that. I used 10w30 in my integra GSR and the transmission shifted flawlessly. That was a long time ago, but I wouldn't have used it if it weren't recommended.

You guys think Honda MTF is pretty thin? I don't personally have experience with it.

Yeah it definitely runs easier than 10w-30 during a Vermont winter. 90's Civics do indeed call for either their MTF or 10w-30. Later D series dropped the motor oil recommendation but most of the internal components that matter (syncros, mostly) still had the same part numbers, so presumably one could have continued using motor oil in later transmissions.

If you're interested enough, I probably have some MTF and 10w-30 in the basement. I could throw a bit of each in a cup in the freezer and see what they do.

Yeah that sounds like a fun experiment. And maybe in the fridge too. Virginia winters probably have an average temp of high 30s or even 40 or 41F. The produce bin of a fridge is probably hovering around 37 or 38 degrees.

I just checked my Honda service manual (so happy the previous owner bought this) and it doesn't mention Honda MTF at all, and recommends using 10w30 or 10w40.

Wonder if I could get away with 5w30, which is used in the engine. It was mentioned in an Ecomod post (think its a sticky) that lighter transmission fluid can reduce fuel consumption a little. Not likely much, but five little things add up to a big thing, and I've just started with this car. And it would be a good idea to change the oil anyway.

Worst case, it doesn't shift well and you change it, right?

I'll toss some oils in the fridge.

Edit: Apologies, looks like I'm either out of MTF or it isn't where I thought I put it. I'll update if I find it.

Yeah I think maybe I’ll try 5w30 and see how that goes.

There have been instances of people using Honda MTF in 90s-vintage Civics and developing major issues quickly. Group consensus at the time was that the MTF was too thin. There may have been a reformulation of the MTF since then? Not sure.

Honda was recommending their MTF for all manual transmissions, which I think was just an effort to sell more MTF and too bad for folks with old cars.

I am certain that anybody's ATF would be the wrong stuff to use. It is definitely too thin and will cause problems.

Honda, at the time, specified 10W40 motor oil for their transmissions. I think 5W30 was also allowed in the owner's manual. I always used non-synthetic motor oil of either of those two weights.

I inadvertently experimented with running less fluid. (Read: Didn't put enough in when replacing the fluid. Forgot that the car needed to be level for the measurement to be correct. Oops.) It took a few months, but I developed input shaft bearing issues. This is a major problem in a D-series transmission; you have to replace it from the inside so lots of disassembly is required.

Zero issues with the motor oil when filled with the proper amount. I would not recommend anything other than non-synthetic motor oil.

-soD