I started my engine yesterday with no preheat at 37F. It was painful and took a couple minutes. It was a good test of my battery, though

I would follow the Lycoming recommendation which is to just start it.

I live in a cold region and have never had an issue following their recommendation. I start down to 20F without preheat. I do use a good multi-viscosity oil and run the engine at 1500 rpm for 5-10 minutes until the oil reaches 100F before takeoff. Below 1000 rpm runs the risk of fouling plugs.

Also, use a primer if you have one, and the engine will start as quickly as on a hot day.

Aaron

Follow up.

I packed the generator in the back of the -10, as the destination airport is a pretty small / unattended place (8C4).

Yesterday the afternoon temps were in the high 40's with sun, and when I flipped the switch the oil temp was 44F so I just started as usual.

Thomas...after Atlantic wanted to charge me $75 for plugging in my airplane without asking when it was 40 OAT, I decided to go this route with an MSR whisper-light camping stove for the days I actually needed to preheat. You just use fuel sumped from your tanks...no power required. Uniformly warms entire engine and takes oil from 25 to 60 in about 30 minutes.

The only negatives I've found...

1. The flame burns very clean and hot, so the stove glows red-hot and takes a few minutes to cool down before stowing in the airplane
2. 100LL seems to plug up the fuel nozzle with lead...I switched to using mogas which leaves a smokey residue on stove

https://www.youtube.com/watch?v=3DGsJpqRFqg

Picture of my rig...all parts weight less than 2 lbs. when bottle is empty

Freezing Point
 

When I was the chief pilot of a small Piper Navajo operation in northern Ontario Canada, we used the freezing temperature as the cut-off for pre-heat. Even the hangar was kept at 40*F overnight. We would push the planes out into -40*F and start them up right away. When out on a charter and waiting outside all day, it could easily be -25*F in the afternoon, so we would preheat the engines and use custom made engine blankets. It was too cold to use a camera, so I don't have any pictures to share ;)

One thing we had to watch was high oil pressure after start. We'd have to idle the engines at 800rpm initially and slowly increase RPM to about 1200 as the oil warmed, thinned and the pressure dropped from the maximum limit. Leaning aggressively to prevent plug fowling.

Engines were Lycoming 6 cylinder angle valve and a big turbo (TIO-540) running multi-viscosity oil. They routinely made it to TBO.

FWIW, I'll probably preheat my plane at warmer temperatures. Not for any concerns about the engine, but to reduce warm-up time and save gas. Plugging in extension cords and setting up engine tents all takes considerable time that a commercial operation doesn't want to waste. On a private plane, I'd rather save that couple dollars of fuel not idling and warming up as long. I plug in my cars at home at 15*F for the same reason.

This is more or less what I use, costs almost nothing in parts from a hardware store. I use my jetboil and carry a couple of cans of fuel, but it's also for making coffee and mountain house should the need arise.

I also have an engine blanket and with this combo I can have the oil temp at 70 degrees in 20 minutes when it's -10 out. I can also shut down, put the engine blanket on, come back in 6 hours and still have warm oil to.

Also... pull the prop through about 6-10 blades on those really cold days. Really loosens things up.