Drlling a hole in old rads

Chris_35

Is it possible to drill a hole in an old (100 years) cast iron rad so that I can add another vent?
Or should I put a vent on the actual steam main?
I have a rad that just does not seem to want to heat up and I think its because there is not a main vent and its at the end of a long run.

Steamhead (in transit)

Vent the main, not the rad

If you over-vent the rad, water will get trapped in the branch line because the steam is moving too fast. This will cause banging.