Roger Long om wrote:

: Remember that the cylinders are designed for efficient transfer of heat from
: metal to air and work that way in reverse. After prompting by our A&P, I
: started looking critically at oil temperature and concluded that the 20
: minute preheats we were getting from the FBO's big blower were not doing
: much for the oil deep down in the pan. There is a lot of thermal mass in
: the engine. As our A&P says, "Have you ever tried to thaw out a frozen
: turkey on Thanksgiving morning?" The oil sump is at least that massive.

I designed my own preheater a couple years aog. It's a 35,000 BTU propane
"utility" heater with some adapters and clothes drier ducts. My 12V to
120V inverter runs the fan, and my airplane footlocker holds the preheater,
inverter, propane bottle, and the wing covers (and about 4,000 other things
that I should throw out...)

I fashioned a device that plugs into the cooling air exhaust behind the
nosewheel on my Cherokee. 20 minutes of heat raises the oil temp from
0F to 50F as measured by a thermocouple attached to the dipstick.
A couple more minutes on each side of the cowling cooling air inlets to
warm the cylinders, and I'm done.

Don't forget the the electric oil sump heaters are between 250 to 500 watts,
and my propane heater is about 10,000 watts (W = 0.29 * BTU). You'd
expect 40 times the heating power to reduce warm-up times.

--
Aaron Coolidge (N9376J)