i have a 98 gle with 100k and since the car was maintained very well from the previous 1 owner i wanna keep that going...anyway i wanna do a drain and fill on the tranny, the question i have is looking in the maintainance logs i notice they have dexron III written in the book so im assuming thats whats in the car. ive been reading alot of the forums on tranny fluid and from what you guys say synthetic is the way to go, i wanna put in the best that i can, so doing a drain and fill would putting in synthetic atf, in with the remaining dexron III be ok or would it be better to keep whats allready in it? oh and just to let you know the tranny fluid still looks nice and fresh , i just wanna do it and know its done for piece of mind ...should dex III and syth. be mixed? thanks guys!!

 

Considering you have to drain and fill and repeat to get a complete or near complete flush, I would just stick with the old stuff.
IMO, your just throwing money away.

 

"Dextron III" is a fluid properties/performance specification...it has nothing to do with the fluids' base stocks being petroleum or synthetic. Just like people on here keep getting hung up on the Nissan-specific specs D, J, K & S and thinking they have to use Nissan branded fluids...they don't. As long as a fluid is labeled as meeting the required specification it's totally acceptable for use. Synthetic transmission fluids offered by the major players are compatible with other fluids (petroleum or synthetic) offered by other manufacturers, so you will be safe in using it as long as it meets D-III.

Be advised, however, as Fakie pointed out you will not achieve maximum benefit of the synthetic fluid unless you do a drain and refill several times to raise the concentration and you run into diminishing returns after the first change or two...that same concept applies whether you're trying to replace the fluid with fresh synthetic or petroleum ATF. Based on calculations I did for my '98 one change will get you to ~50%, second change up to 75% new fluid, third change 88% and fourth change 94%. I changed my '98 to AMSOIL (ATF and motor oil) at the 1,000 mile point and the transmission continued to work flawlessly until the vehicle was was totaled with over 200K on it.

Whether you go with synthetic or not, the good news is that the car was well maintained and you're interested in continuing with that practice. Good Luck with it!