I've not been able to achieve proper temperatures with my >10 y/o WSM 18". I've used chunk and briquettes (last night) and it just doesn't want to come up to temp. Minion method, all vents open, cleaned WSM.
Dome dial, you mean the thermometer that came with the WSM. Have you tried cleaning the probe off. After 10 to 14 years a lot of crud could be covering stem. Also is your WSM warm to the touch? It sounds like your minion method is burning to slowly, maybe start it off with more lit coals.
Well, took out the thermometer and it was covered. Cleaned her up and did a two-point test and she seems to be operating properly. I guess I'll have to smoke something soon to test her out. I'll use another thermoprobe inside the dome as well.