These oil pan "pad' heaters are an accessory to "block" heaters only. They are not effective on their own. They have applications, but oil pans on passengers cars is not one of them. They are too exposed to the wind/elements and the adhesive is not a good conductor. That is why ppl use the "magnetic" heater, but then it too has some major drawbacks as they don't work on aluminum or ribbed surfaces.
Install a "circulating" heater. Those things are awesome.
