Marty is correct; yours was not operating correctly if it did what you claimed previously.

Mine only comes on when I exit the freeway on +100F days and enter into stop and go city traffic. This creates a spike in coolant temps to 95-100C at which time the aux fans engage. Is very noticeable.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)