Originally Posted by VictorII
I'm pretty sure all T5s use ATF due to smaller oil passages. Use synthetic and it is even better. Anything thicker will clog passages according to what I have read. I oly use Mobil 1 in my T5. When I had a Dodge van with a 3 speed, I used ATF in that, too. Mainly because I was in cold climate about half the time; it was recommended in the shop manual as al alternative which surprised me. but it worked fine. However, I've never heard of motor oil in a transmission unless that is all there is and the driver can't wait. Hope the T5 in that '97 is ok...
Auto trans fluid is typically like a 5w15 viscosity, most of the additives in it are the same as those in motor oil. The red dye of course makes no difference, so it probably wouldn't have caused any damage. I guess if it was pushed hard in extremely cold temps the shift action might be slower until the oil warms up.