Originally Posted by JCL

I have used these same pads (or very similar) on larger engines without any issues.

First point is to not trust your temperature gauge, it isn't very accurate. It has three positions, essentially, according to the buffer and programming built into it. Left is cold, right is too hot, and anywhere remotely close to the right temperature results in straight up. Analyzing it beyond those three conditions is fraught with risk.

You can't leave it on too long. It can't boil the oil. Once you determine how long it takes to reach equilibrium, however, any more time is just wasting electricity. Move it up an hour or two and see if it makes a difference. It shouldn't take any more than 3 or 4 hours IMO.

You can't warp the pan. You may contact the splash guard insulation or something else that doesn't like heat, but the pan is fine. Again, IMO.

If you have an oil immersion heater, you can get coking of the oil on the element, not good. Given how these silicon pads mount, they are very safe.

To put it in perspective, my four cylinder Volvo block heater was about 500 or 600 watts, mounted in the water jacket. It took 2 hours to get to equilibrium in Edmonton winters. I had one vehicle with a 1200 watt block heater, again, in the water jacket. It was hot in an hour, it was like plugging in a kettle (1500 watts).

You mention your battery. Are you using a battery blanket? A 50 watt blanket from Canadian Tire will make it turn over much more reliably. That does not need to be plugged in as long. We always used automatic timers.

If the interior of the vehicle feels like a block of ice (and it will) then get an interior car heater.

We would mount multiple heaters (jacket water, oil pan, battery blanket, interior) and run them all to a common power bar, on a timer. When I left in the morning I would unplug, and plug in my wife's vehicle so that it was ready an hour later for the school run.

Haven't used a plug in since 1990, but remember the drill very well.