This is the advice I gave on an earlier thread. When taking advantage of the coefficient of thermal expansion, it should make no difference whether one uses heat or cold.
Well that seems like it would depend on which part you are heating or cooling... In general for whatever reason, heat always seems to work the best, probably because you can heat it up more than you can cool it off...
When installing control arm bushings, you put the bushings in the freezer and heat up the control arm, they almost slip right in.