T-5 Fluid

correct...2.8 quarts or something like that

It's actually Mercon AFAIK. Same difference but I hate it when folks call our LSD's posi's as well.

mercon.

I use syncromesh in all my t5s

Synchromesh is recommended for the Tremec TKO transmissions but not the T-5's.

Mercon

Just used regular ATF for Ford vehicles. I filled mine with the fill plug out, then when it drains out that hole, wait for it to stop, then put the plug in. I used plain old Valvoline.

Don't they make dexronIII with mercon. I think that is what I put in mine. Shifts like a dream now.

All t5s take mercon dextron III or equivelent.

It seems to me that Mercon is a fluid meeting spec's for Ford, whereas Dexron is GM. It just happens that the characteristics are fairly close between the two, hence their sharing bottles.

Be careful with blanket statements about ATF. Type F, +III, and other ATF's might not be a real hot ticket inside a T5.

I've used Mobil 1 Synthetic ATF without any problems.
See Here... Mobil 1 Synthetic ATF

I was contemplating this the other day when picking up three quarts to change my fluid again this year. I was tempted by that Mobil 1 ATF, but decided on the Hurst Hot Shift fluid. I don't expect it's going to shift any different at all, of course, I just hope it'll hold up a little longer over time than the cheap stuff that might tend to break down a little quicker. Its specifications on the back read for DexIII/Mercon.

Someone slap me if I'm wrong here, but as far as a T-5 goes, the main things to worry about are viscosity and additives. You don't have those teeny-tiny rat-maze passages and whatnot in a T-5 like you do in an AOD, so the useage is a little less complex. You obviously don't want to go pouring 75-140 gear lube in there because it'll be hard as hell to move the shifter and it'll turn to solid snot in winter, but you don't want to run cooking oil in there, either, because you need SOME protection. You also don't want anything weird in there that can react with any of the materials of the internal components. The '94 Probe GT that I had was really anal about specifying ONLY using (IIRC) GL-4 gear fluid in the tranny; using GL-5, which apparently has some kinda sulfur content, would chew up the brass synchro gears in there. So, as long as you stick with any Dexron-III/Mercon equivalent, you should be fine.

On a side-note ... does anyone know if Mercon V is safe to use in a T-5?

I know you can flush the tranny on an AODE or 4R70W and use Mercon V in there to help avoid that whole torque converter shudder problem, and I remember reading that it's either a synthetic blend or a full synthetic. I haven't poured in my Hurst fluid, so if Mercon V's kosher enough to use, I might give that a shot, instead...

Heh ... my tranny's been whining for the past two years more than my ex-girlfriend.