My 93 Toyota Supra has about 80k miles now, and after years of work and changing parts, the transmission is still not working properly when it’s cold. HKS oil is working great in the engine now, but Gm synchromesh 75w90 in the transmission I’m thinking is a problem. What oil is going to perform the best in all temps and has a low poise rating?
I'm not familiar with your Supra so these are just general recommendations. Red-Line gear oil has a very good reputation. I've found that Honda MTL works great in the manual transmission of my '86 Saab, a car with a reputation for a notchy and fragile trans. Makes a noticeable difference in cold shifting and smoother shifting overall. Since your transmission is obviously a different design your mileage may vary. Possibly a forum devoted to that car would have more specific information.
This Supra-specific forum might be a good place to pose this and other Mark IV -specific questions
https://www.supraforums.com/forums/mkiv-1993-1998.33/
I did a quick search but didn't see a good thread on it
https://www.supraforums.com/search/930284/?q=manual+transmission+fluid&t=post&c [child_nodes]=1&c[nodes][0]=33&c[showFilter]=visibleOnly&o=relevance
But you might want to join and post the question - this site would be a good place to obtain manuals and parts as well as recommendations
Since Honda is GL-4 they are an option, I’ve heard nothing but complaints still of people with redline. Hks can’t be used since they don’t offer a gl4 to the public.
@christianlouis I tried Redline quite a few years ago. A lot of people swear by it (or at least did at that time in the early 2000s). I found it to be OK but found that Honda MTL produced better results and is less expensive. Have been using the Honda product for about 160,000 miles so if it were going to cause any problems it would likely have happened by now.
This may not help much but my 2010 KIA Ceed has a 90 HP 1.4 L engine and a 5 speed manual. I changed the transmission fluid at 131 K km. or 80,000 miles because I do not tow but sometimes carry the maximum allowed cargo weight. It takes 2 liters of 79W90 and the KIA dealer did the job. I have recently passed 150K km. or 90K miles and the transmission is fine.
