Is it important to use Honda transmission fluid in 99 Civic SiR?
 

I had the car's clutch replaced a while ago (well, like years ago now, but I've barely driven the car since then), and the shop did the transmission fluid at the same time. But they used standard 5w30 oil for it, even though I brought a couple bottles of Honda transmission fluid for the job.

I watched an Eric the Car Guy video recently in which he said to always use the Honda fluid, and so I'm just wondering how important it actually is, and if I should drain what's in there to put Honda fluid in.

Old Honda transmissions used motor oil, its specified in both the owners manual and service manuals I have for 91 civics. After that (92-95?) I believe they started noting to use HMTF and only use Motor Oil in an emergency.

Looking at the service manual for the 99 Si (USDM Sir) it says to "only use HMTF", although only says that "Using motor oil can cause stiffer shifting because it does not have the correct additives".

Id use HMTF just to try and stay away from issues down the road. It will have a different additive pack specifically for the transmission, and its what Honda designed it around. Cheap insurance, simple job, may as well use what the service manual says.

Not super relevant, but food for thought. My brother had lots if issues with his trans not running smooth (auto) in his 99 civic. Had the fluid and filter changed and all that junk. Everywhere on the internet said he should change it to genuine Honda fluid. He took the risk and put in Honda fluid and it solves all its problems. Kinda weird and not sure why. I wouldn't have believed it if I didn't help do the work and witness it

I'd only use OEM fluid in a Honda. I find they work best.

Use GM synchromesh.. trust me.

I've been using honda MTF on ALL my hondas.
It is also cheaper than other branded ones.

i personally find it cheaper buying it from ACURA dealers. i bought 2 last week for $9 a bottle

I would stick with the Honda MTF also. Whatever additives are in there seem to work well in the manuals.

On a side note...I remember way back in the early 90's. Some of the 90-91 civic's with manuals made a weird humming noise when making a sharp turn. Turns out it was coming from the diff in the trans. Either a bulletin or the techline (not sure if they were even around then) told us to use Honda ATF instead of the 5-30 and that did solve the problem. This was way before the Honda MTF was around' which I think it came out somewhere in the mid 90's

Hondas are like the only cars which I own that it seems like you have to use the OEM fluid.
ie: Automatic transmission, power steering fluid, rear differential (dual pump fluid), coolant

These fluids are supposedly not the same as regular OTS fluids.

For engine oil, brake fluid and MTF, I used whatever brand I wanted.

Was just going to mention this. Remember reading about this on the Acura forums when people were having random issues with their manual trans. Solution always ended up being to switch to gm syncromesh fluid.

I've been told syncromesh can eat at the brass syncros in these transmissions. Personally, I'd stick with Honda mtf. Especially if you're​ not intending to mask an issue and are just doing a service

Here's a quote I just found looking it up.

I used Honda MTF in my EM1 recently.