Honda CLARITY 2021 Owner's Manual page 21

Fuel Cell Insulating Fluid
Fuel cell insulating fluid (FC insulating fluid) uses a specifically designed fluid with high electrical insulation properties in order to safely cool
the fuel cell.
Never add water, other commercial coolants, or genuine Honda inverter coolant to the cooling system. Doing so will cause damage to the
fuel cell.
Consult an authorized Honda Clarity Fuel Cell dealer to replenish or change the fuel cell insulating fluid.
Inverter Coolant Reserve Tank FC Insulating Fluid Reserve Tank
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