Manual Tranny Fluid
 
Because of changes in motor oil chemistry starting around 1990, the correct lubricant to use in any Honda manual transmission is OEM Honda MTF. What happened around 1990 was that "the oil companies voluntarily reduced the amount of zinc content in most of their products after research indicated the zinc was responsible for premature deterioration and damage to catalytic converters." (See Is that Additive Really a Negative?, Road Rider Magazine, 1992.) But certain zinc additives are said to assist in "extreme pressure" conditions. (See Wikipedia, Motor Oil.) Thus a new lubricant with the right amount of zinc was needed. Today Honda Motor Company's literature states that the manual transmission fluid to use is Honda MTF. This overrides what older Honda automobile owner's manuals say about using ordinary engine oil (10W-30 or 10W-40) in the transmission. Further evidence to support this follows.
 
  • http://www.honda.com.au said c. 2005: "Honda MTF Plus Manual Transmission Fluid has been specifically formulated for use in all Honda manual transmissions. MTF Plus is designed to provide smoother shifting operation at all temperatures over the life of the fluid."
  • From the 2002 RS-X owner's manual, page 13-4: "Always use Honda Manual Transmission Fluid (MTF). Using motor oil can cause stiffer shifting because it does not contain the correct additives."
  • From the 2005 Civic owner's manual (and I'm betting all of the more recent owner's manuals): "If Honda MTF is not available, you may use an SAE 10W-30 or 10W-40 viscosity motor oil with the API Certification seal that says 'FOR GASOLINE ENGINES' as a temporary replacement. However, motor oil does not contain the proper additives, and continued use can cause stiffer shifting. Replace as soon as it is convenient."
  • Many reports on the net attest to the better shifting with the Honda MTF. I switched to the Honda MTF in September, 2006 and think the shifting is smoother, though not profoundly.
  • The Honda MTF container says on it that one may increase the time between MTF changes by using it.
  • Lastly, to me the clincher: The 2005 Honda Civic owner's manual gives a maintenance interval for the MTF of 6 years/120k miles for normal driving conditions. Contrast this with my 91 Civic owner's manual maintenance interval for the MTF: 2 years/60k miles for normal driving conditions. Going by the years limiter, the cost of using the Honda OEM MTF ($12/6 years) is about the same as that of using ordinary engine oil ($4/2 years). To me the chatter on the net added to what Honda says in its manuals and at some sites means one is erring on the safe side by going with the OEM Honda MTF.