Well now you do 🙂
I have read that larger power plants are more heat efficient though, so while scooping for example, the ship will heat up slower and cool faster.
Although, I have not experimented with this myself. An easy trail would be firing off a SCB in a ship, recording the heat level, then down/upgrading the power plant by a whole size, and trying again. It could explain the FDLs ability to not overheat since the bigger power plant was made available for it.