When changing the tranny fluid the manual dictates a 75W90 (MT 90) for the temperatures in most of North America.
Most of us prefer Redline Synthetic Oil products for use in the manual transaxle because it improves shiftability and gives you a plus of a synthetic oil in the manual tranny. Several prefer Mobil 1 synthetic, BUT Mobil does NOT recommend it in a transmission that requires GL-4. Go here for more info.
The SR20DE's tranny requires approximently 4 quarts of oil.
Comments by Michael Kruger
I have spent a week now with MT90 in my trany. Great stuff....everyone ought to get it. Shifts are much more smooth and there is no mollassis shifting start-ups anymore. I am in New England so when it gets to 20 below zero, I will REALLY appreciate it.
MTLŪ - Manual Transmission/Transaxle Lubricant. A 75W/80W GL-4 gear oil which is designed for manual transmissions which require 75W or 80W GL-4 gear oils, motor oils, or ATFs. It provides low temperature shiftability equal to an ATF, yet will not thin out or shear at high temperatures and provides the substantial gear protection of a GL-4 gear oil. The higher synchronizer coefficient of friction allows faster upshifting and downshifting and the lubricant is non-corrosive to synchros and bushings.
MT 90 - Manual Transmission/Transaxle Lubricant. A 75W90 GL-4 gear oil which is designed for manual transmissions which require 75W90, or 90 GL-4 gear oils or motor oils. Uses the same chemistry as MTL , but is a 90 WT in order to satisfy certain manufacturers which recommend SAE 90 GL-4 gear oils.
More from the bottle:
Red Line Synthetic MT-90 is specially designed for manual transmissions and transaxles. The relatively constant viscosity over a wide temperature range allows easier shifting and helps prevent whine and rattle at high temperatures. Most gear oils, ATFs, and motor oils are too slippery for proper synchro engagement - which causes gear clash when shifting. .... MT-90 has a coefficient of friction which is perfect for rapid synchro engagement and allows high-speed upshifting and downshifting. ... Petroleum multigrade motor oils and transmissions fluids contain polymers which shear down rapidly under the action of gear teeth and rapidly lose viscosity , significantly reducing their lubricating ability . Red Line MT-90 is shear stable and will retain its physical characteristics for extended periods. MT-90 meets gear oil viscosities SAE 75W, 80W, and 90 or motor oil viscosities SAE 40 or 15W40 and provides gear protection which satisfies API categories GL-3 and GL-4.