Now when coolant has its buildcraft liquid form, it can be used for engines and stored in tanks. But You lose resources when you store them in tanks because cell just disappears. So my idea is to a empty version of coolant cells . They would be stackable and they would be returned to you when you pour coolant to tank cart, tank etc. and they would become coolant cells when you empty tank with them and maybe they would rarely appear in reactor when coolant cells evaporate so they would be able to fill them with proper amount of water to gain new coolant cell.