Do this:
1. Use a XM214 Minigun
2. Go next to a turret (but don't step into it to use it yet!)
3. Shoot your minigun (don't run out of ammo) and walk into the turret at the same time
4. Continue firing the turret until it overheats
5. Step out of the turret, still holding down the shoot button.
6. Now you're supposed to be firing your minigun, and the turret is seemingly cooling down to normal.
7. Step back onto the turret, still firing.
As soon as you're on the turret and using it, your shoot button still held down, the turret is still overheated. Now, if you didn't shoot the turret till it overheats but it has gained some heat, then the heat that had been gained will still be there.
This shows that if you step out of a turret whilst still holding down the shoot button, the heat meter is paused. However, if you release the shoot button anytime, the heat meter cools and won't pause again until you do this again.
