Is this a sign of a bad cat or just fluid burning off of it. I bought my car as a project, it had a tranny leak and lots of body rust. And when I bought it smoke came off of the cat from(I believe) transmission fluid spraying on it. I have put on about 600 miles since I got the tranny leak fixed, and it is still smoking after long drives(2 or 3 hours). Is it still burning off fluid that has acumulated in it or is the Cat bad?

 

I would check for an oil leak or another tranny leak.

 

I had a trans leak that did the same, cat was fine though.

 

The smoke was whiteish colored, almost not there. I didn't smell anything specific burning either. Also there was no dripping on the ground or anything, so I don't think I am leaking anything.