i decided to finally change out all fluids in my car (changed the oil the day after i got the car, but the rest have been neglected). i started with the diff fluid, which was a pain in the ***, but i at least figured out what fluid i needed easily. now i need coolant and trans fluid. for coolant, i have a bunch of prestone regular antifreeze (says it can be mixed with any color), and just bought a gallon of prestone dex-cool. can i mix these two in the cooling system? or do i need to go and buy another gallon of dex-cool? and about transmission fluid...the manual says i need automatic transmission fluid. i went to autozone to go buy some, and had no luck figuring out what i actually need. there's mobil 1, which is the most expensive at $10/qt, and on the back, it says its not recommended for some gm transmissions. Then theres valvoline, which is pretty cheap, at around $6.50/qt, and is specially formulated for chrysler or something like that. and finally castrol, at around $7.50/qt, is the only synthetic blend (the others are full synthetic), and is recommended for gm hydra-matic transmissions or something. i have the t-56, so what the hell should i get? any? all? pixie dust? thanks.

 

For the T56 trans, you need the latest version of GM's Dexron ATF (I think they are up to Dexron-VI). Your Owner's Manual (Page 7-23) shows you need Dexron-III. But if they have a higher numbered Dexron, it is backward compatible with the lower number versions. I wouldn't use anything but the non-synthetic ATF. Who knows what synthetics will do to the synchros and blocker rings? But if it says it is compatible with Dexron, you can use it if you want. I loaned a spare T56 to a buddy, who wanted to see if his trans was the source of some vibrations. He filled it with some Honda ATF that was raved about on the Internet. When he brought it back, it was making some awful noises.

I would use only the specified Dex-Cool coolant. Why risk mixing two different kinds? It seems odd the Prestone "regular" (do you mean "green") is claimed to be compatible with Dex-Cool. I thought Prestone made a "yellow" coolant that is supposed to be compatible with regular "green" and Dex-Cool "orange".

 

so you would say to use any dexron III+ thats non-synthetic? gotcha, that sounds cheaper than full synthetic

and i think the regular is green, yeah. theres a huge thing on the label that says you can mix it with any color. i used it in a saturn before, and it didnt seem to cause any problems, but who knows? ill go get another jug of dex-cool. i can use the regular stuff on some of the other cars i work on.