NOVELTY - A deionization filter (10) for de-ionizing a coolant in electric fuel cell vehicle, comprises filter assembly for filtering particles from coolant; ion exchange bed for removing ions from coolant; and conductivity meter system comprising first conductivity meter connected to coolant inlet port, second conductivity meter connected to coolant outlet port and conductivity analyzer box for determining ion-removing efficiency of ion exchange bed.    USE - The deionization filter is for de-ionizing a coolant in an electric fuel cell vehicle (claimed).    ADVANTAGE - The deionization filter maintains low electrical conductivity of the coolant and prevents short-circuiting of the fuel cells which drive the vehicle.    DETAILED DESCRIPTION - A deionization filter for de-ionizing a coolant in an electric fuel cell vehicle, comprises:    (1) a filter housing (12) having a coolant inlet port (16) and a coolant outlet port (36);    (2) at least one filter assembly (27) provided in the filter housing for filtering particles from the coolant;    (3) an ion exchange bed provided in the filter housing for removing ions from the coolant; and    (4) a conductivity meter system comprising a first conductivity meter confluently connected to the coolant inlet port, a second conductivity meter confluently connected to the coolant outlet port and a conductivity analyzer box operably connected to the first conductivity meter and the second conductivity meter for determining the ion-removing efficiency of the ion exchange bed.    An INDEPENDENT CLAIM is also included for a method of removing ions from a coolant in a vehicle coolant system of a vehicle, comprising:    (1) providing a deionization filter having an ion exchange bed in the vehicle;    (2) distributing the coolant through the deionization filter; and    (3) monitoring an opening efficiency of the deionization filter by connecting conductivity meters to inlet and outlet ends, respectively, of the deionization filter and a conductivity analyzer box to the conductivity meters and determining a pre-ionization conductivity and a post-ionization conductivity of the coolant.    DESCRIPTION OF DRAWING(S) - The figure is a longitudinal sectional view of the deionization filter.    Deionization filter (10)    Filter housing (12)    Coolant inlet port (16)    Cap interior (21a)    Filter assembly (27)    Coolant outlet port (36)