Rumble is able to use his E while cooling
While cooling i usually cannot use abilities but sometimes I could use his E.
While cooling i usually cannot use abilities but sometimes I could use his E.
His E has two casts. If he overheats on the first cast, he can still use the second cast of his E.
If the first cast of E caps your heat, you can still use the second while cooling.
That is how it should be working.