During the brawl among the Primitives, Grimlock showed the upity Decepticons not to insult him by unleashing his fire-breath upon them. The Decepticons hit started to cough...cause that's what happens when you get him with fire that can melt body armor. Call of the Primitives It may be possible that Grimlock deliberately turned down the power of his breath, wishing only to subdue the Decepticons (since at the time he was allied with them), but a) this is only speculation, and b) Grimlock isn't that smart (or at least wasn't in the G1 cartoon).