I will guess.
Thermostat may be stuck or intermittantly sticking "open".
Because...
210 isn't that abnormal although in cool weather it's a little high,
and, 180 is normally cooler than the thermo in a 94 would allow it to drop to.
The fact you're seeing a 30ยบ "cycle" after the engine is hot suggests a thermostat issue or a "cooling capicity" issue. Since you've confirmed the radiator isn't partially plugged (if it is that would be another possibility) my guess would be look at the thermo.
Also if you were low on water you might see this pattern.