A method for filling a cooling circuit of a motor vehicle with a coolant may include filling the cooling circuit with ion-free water in a water filling operation, leaving the ion-free water in the cooling circuit for a water duration of action in a water operation of action, displacing the ion-free water out of the cooling circuit via filling the cooling circuit with a passivating agent in a passivating operation, rinsing the cooling circuit with ion-free water such that the ion-free water at least dilutes the passivating agent in the cooling circuit and a liquid including at least one of the ion-free water and the passivating agent remains in the cooling circuit in a rinsing operation, displacing the liquid out of the cooling circuit via filling the cooling circuit with the coolant in a coolant filling operation, and/or fluidically sealing the cooling circuit towards an outside in a sealing operation.

The present invention relates to a method for filling a cooling circuit (2) of a motor vehicle (3) with a coolant (4). A simple filling of the cooling circuit (2) with coolant (4) and an increased operational safety are achieved in that the cooling circuit (2) is initially filled with ion-free water (13) and thereafter with a passivating agent (16), and wherein thereafter the cooling circuit (2) is rinsed with ion-free water (13) and subsequently filled with the coolant (4).

The invention, furthermore, relates to a system (1) for filling a cooling circuit (2) of a motor vehicle (3) with coolant (4).

Disclosed is a pre-treated ion exchange resin comprising at least 15% by total number of exchangeable groups comprising at least one of an ion, or a Lewis acid, or a Lewis base resulting from a heat transfer fluid component having a pK.sub.a or pK.sub.b of greater than 5 in an aqueous solution at 25 C., based on the total number of exchangeable groups. In one embodiment, the heat transfer fluid component is at least one of a colorant, a corrosion inhibitor, an antifoaming agent, a bitterant, a dispersant, or a combination thereof. In one embodiment, the heat transfer fluid component comprises a heat transfer fluid corrosion inhibitor. Also disclosed are heat transfer systems, assemblies, fuel cell systems and methods of maintaining a conductivity of less than 200 S/cm in a heat transfer fluid that employ the disclosed pre-treated ion exchange resins.