Dextron Mercon III

I put about half a quart on DEX/MERC transfluid into my transmission.
Will it hurt it?

Put it in what?? I don't see what year and all that stuff. That little bit probably wont hurt it but you might want to think about tossing in a bit of Lucas or Lubegaurd or something of the sort just for insurance. It's usually a good idea in these things anyways, in my opinion.

Its a 2004 voyager. I agree, the small quantity probably has minimal impact, but I thought I should ask. Good suggestion about the lucas.

Your transmission holds in the neighborhood of 9 quarts of fluid. I agree 1/2 quart won't make much difference. I'm not an additive advocate. At most I would schedule the next fluid/filter change a tad early - maybe at 3/4 the recommended interval.

The Dextron Mercon III will ruin the tranny, even for adding a small amount. The fluid is incompatible with the ATF+4. Lubegard is to be used if ATF+3 is your only other option.

The chemistry makeup of the DM-III will cause wear and clogging issues with the tranny. A chemical reaction in the tranny will be when the white foam gets so bad, it leaks out of the tranny dip stick tube.

Yes, I read that all the time but I'm not as hard over on it as I once was after reading a post from a guy who had Mercon in his 41TE for 3 years without a hickup. He wondered if he should change to ATF+4. Never heard what he finally did. Still not an advocate for using a full fill of anything but ATF+4.