I have one and it gets plugged for the past couple of days but I have no clue if it is actualy working whats the best way to test it ?

I didnt notice any change in temps on cold mornings car takes as long as it always did without plugging it

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2003 GX470
1998 E300 3.0TD
2002 Dodge 2500 4x4 cummins
1998 Dodge 3500 5 speed Cummins