Patent ID: 6989680

Claim:
A method of monitoring the presence of engine coolant contamination in lubricant comprising: (a) disposing at least two electrodes in the lubricant and applying a relatively low voltage alternating current to one of said electrodes and sweeping the frequency of the voltage over a predetermined range; (b) measuring the current and phase angle at a second of said electrodes at predetermined frequency intervals during the sweep and computing the reactance and resistance at each current measurement; (c) determining the least value of reactance Z″ min from said computing; (d) selecting a frequency f i , less than the frequency corresponding to Z″ min ; (e) exciting said one electrode with said voltage at the frequency f i and measuring the current and phase angle at said second electrode and computing the reactance Z″ i and the resistance Z′ i ; (f) determining the parameter Θ = arctan ⁢ ⁢ Δ ⁢ ⁢ Z ′′ Δ ⁢ ⁢ Z ′ , where ΔZ″ is the change in reactance (Z″ i −Z″ min ) and ΔZ′ is the change in resistance (Z′−Z′ @Z″min ); and, (g) providing an indication that coolant contamination exists when Θ reaches a predetermined value.