I've got conventional Dex III in my '99(tranny). Can I do a drain and fill with M1(syn) ATF?

I know this will create about a 50/50 mix of the two fluids. Is this O.K. to do.

I'd rather not do the T-Tech flushing.

 

i emailed Amsoil about this and they said it was ok. they recommend a full flush but its perfectly normal. also its not a 50/50 mix. its more of 30/70 mix. its about a 10-12 quart system, drain and fill only does about 3-5 quarts.

 

The only way I have serviced the transmissions on my Nissans is by doing a drain/refill per the factory service manual. I also use synthetics (AMSOIL) and it is in fact perfectly ok to mix the syn fluid with the dino fluid in the transmission. Of course you won't get the full benefit of the synthetics until you do several drain/refills to raise the concentration to 90%+...and it will take several drains/refills to achieve that level for the reason Turtle cited.