Craig, I did some research on these oil pan heaters for my diesel and gasser. On my 92 Dodge Cummins I have 12 litres (11.3 quarts) oil, about same on transmission fluid. I am going to buy Woverine heat pads for both, the oil sump takes a 250 watt pad and transmission a 125 watt pad.
I talked to the rep from Wolverine, these Wolverine pads WILL NOT burn the oil or transmission fluid. Many do, some heat pads can only be used directly after shut down till next start up. Apparently, Wolverines can be used when engine has been -40 for days, the Pad can then be plugged in with no oil burn or scourge, in 4-5 hours the oil will be +160F and top interior engine 65 F. Many have told me to use block heater too.
Thing is, up here winter is -10 to -40, my block heater is 850 watts and I plug in this 1000 lb motor for 14 hours prior to start with no warmth on oil. This winter I will plugin 375 watts of heat pad for 4 hours (transmission & oil sump pads) and block heater last two hours on timers, this will give great warm start at anything winter can throw at me IMO. (I will heat transmission with pad this winter because this Dodge auto transmission is a nightmare to get into OD in cold weather, will not warm up for nearly 1/2 hour, stays in drive, I think the pad will eliminate that problem and lengthen transmission life) I am using oil and transmission pad on new X-Trail Nissan too.
Cyprs