Just for grins, here's Redline's own commentary on the difference between 5w/30 engine oils, and oils made SPECIFICALLY for manual transmission use... .
Also note that they make NO claim that their 5w/30 transmission lube meets the DC 9224 spec...
http://www.redlineoil.com/redlineoil/mtlti.htm
For those too lazy to go read the whole bit, here's the heart of the piece:
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Viscosity of common lubricants at 0°C (32°F) is compared with Red Line MTL in the chart below. Note that the viscosity of ATF and 10W30 motor oil seems to be adequate. These lubricants are not well suited for transmission use because of two factors - shear stability and improper coefficient of friction - which will be discussed in more detail later. At even lower temperatures such as -17. 7°C (0°F), the differences between conventional lubricants and Red Line MTL are even more dramatic. At such a temperature many of these lubricants would prevent shifting into certain gears, depending on the design of the transmission.
All oils are slippery, and with most lubricated components, the slipperier the better, but this is not so with manual transmissions. The synchronization of shifting gears requires friction to transfer energy from the synchronizer, which is locked to the input shaft, to its mating surface attached to the gear to be locked in as the drive gear. Few modern transmissions use sliding gears to change gearing other than for reverse gearing. Synchromesh transmissions have the gear pairs constantly in mesh. The drive gear is selected by using the shift forks to slide a synchronizer ring, which rotates at the same speed as the input shaft, in contact with the selected drive gear. Once the drive gear is brought to the same speed as the input shaft, the locking ring on the synchro assembly is allowed to slide over and lock into the drive gear.
The time this process takes depends on how easily the synchro ring moves and the rate of frictional energy transfer between the two synchronizer surfaces. Higher viscosity lubricants slow the sliding of the synchro ring on the input shaft and require a longer time for the oil to be squeezed out from between the mating synchronizer surfaces. After the lubricant is squeezed out, the coefficient of friction of the lubricant determines the rate of frictional energy transfer between the two surfaces. Slippery lubricants such as hypoid gear oils and ATFs can take too long to synchronize the gears, which promotes synchronizer wear. Red Line MTL and MT-90 has a coefficient of friction which is greater than conventional oils, allowing a quicker transfer of frictional energy.
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The above - and additional info in the article - all pretty well points out that an oil designed and intended for ENGINE use, where MAXIMUM friction reduction is needed, is NOT what works best in a transmission - and is why any off-the-shelf MOTOR oil probably is not the best choice for long-term manual transmission use - and for that matter, *I* sure wouldn't want an ENGINE oil that also carried a manual transmission spec in my ENGINE, either!
Engine oils for engines, transmission oils for trannies!
