I want to replace my 100amp service to 200amps the meter pan looks original I had to pull the meter to do some work, I notice that it was wired with what looked like 8 gauge wire this is an old meter the garage was built in the 1930's. The wire from the drop is 2 gauge as is the wire leaving the meter pan, how can this be all the amp load through 8 gauge wire ?

Just because the service was rated 100 amps, does not mean the amp load was 100 amps.

Seems the #8 wire was sufficient for the load, assuming it is not overheated or damaged in any way.

Someone was just very lucky all these years.