Abstract: An apparatus and method for removing particulates, hydrcarbons (such as oil), cations and anions including nitrite ions from a liquid, such as an engine coolant liquid having a freezing point depressant and situated in an internal combination engine cooling system. The apparatus has at least one filter for removing particulates and hydrocarbons; a strong acid cation exchange bed in the hydrogen form for removing cations; a strong base anion exchange bed in the hydroxide form for removing anions; and separator for separating gas containing nitrogen, such as nitric oxide and/or nitrogen dioxide, that is produced in the cation exchange bed and/or the anion exchange bed.