The in-the-dipstick-tube ones are all I've ever seen. Seem to get too hot and oil burns onto their surfaces. Never used one, but block heaters that replace a freeze plug seem to work really well. Water carries heat to entire engine so it doesn't need to be as hot as warming oil only.
I have a 250 watt Wolverine pan heating pad adhered to my pan. Have been using it for several winters. Usually leave it plugged in all the time when temp is below freezing. I like it. Easier winter starts and warms up quicker. Oil does get cooled by the block once you start, but still a lot better than with cold oil. I should get a smaller pad for the tranny because the 1-2 shift is very stiff and chunky when cold.
I totally agree with TallPaul on the benefits of pre-heating the oil and ATF. I have similar setup on my car with 125 watt Wolverine heating pad for the oil pan, 100 watt heating pad for transmission pan plus a factory 400 Watt engine block heater.
I just ordered the 125 watt 3 inch round wolverine oil pan heater, I wanted to get in installed before winter and it was pretty cheap. Do you guys use some type of fasteners or hold down straps when you route the plug in cord from the oil pan to the front of the car?
I plugged in the Wolverine oil pan heater, the engine block heater, and the transmission pan heater for 35 minutes on the first freezing morning last week. With my pre-luber pumping the hot oil from the oil pan the dummy low oil pressure warning light dimished immediately before I cranked up the engine. I noticed the oil temperature reached 170F. As I drove the car the oil temp slowly dropped below 140F, the lowest reading on the gauge. I assume the oil was cooled off as it traveled to colder part of engine. But after 10 minutes of driving the oil temp came back to 140F and climbing. That was quite fast considering it usually took 15 minutes of driving for oil to reach 140F on a 76F morning without the use of any heating devices.
So, I am not sure if the Wolverine itself will be able to warm up the entire engine as the vendor claims without the help of an engine block heater under a freezing temp, but it definitely helps during the engine startup.
They are sold on several different websites and the recommendations for how long they're supposed to be plugged in range from 2 hours to 6 hours. I'll be ordering one for each winter car very shortly and plan on leaving them on a timer from about 3am until I leave in the morning (between 7am and 8am). Warm coolant is nice for the driver to get heat right away but warm oil is nice for the engine. I would imagine if the oil heater is on long enough, the engine and coolant will warm up faster and hence the driver will get heat faster.
2 to 6 hours? I wonder under what kind of temp that dictates the length of operation. I am concerning that the heating pad might burn the oil at the bottom of oil pan because it can get really hot as I touched it with my hand once.
The back side of Wolverine that sticks to the oil pan is metal with adhensive which makes heat transfer very effectively. It is very well designed. The transmission pan heating pad I bought from eBay is of older design that has its heating element entirely covered in rubber and was glued to the pan with additional scilicon that acts as an additional insulator. Despite being rated at 120W (only 5W less than Wolverine) it just did not feel as hot as Wolverine when I touched both them, but it costs a lot less.
re metal to metal contact - are they compatiable?(i.e. copper/steel is a no no ) is electroisis a possiblity?In a salty enviroment could corrosion be a issue,some oil pans are a big job to change out . just rambling out loud.
The metal backing of Wolverine is definitely not copper. It has a stainless steel color. A tube of scilicon RTV sealer was included in the kit to be applied around the edge of pad for weather proofing. I guess it was for corrosion prevention as you suggested in a salty environment. The instruction also calls for scrapping off the paint off the oil pan where the pad will attach for better adhesion. I did not follow that particular step but only cleaned the surface with paint thinner as instructed to remove grease out of fear of future rust issues.
I installed the wolverine oil pan heater I bought a few weeks back, easy install to say the least. Anyways I've plugged it in for a full eight hours before (before I go to bed), is that what everyone else does or is that too long?