I think @Peter is right. The crankcase is somewhat closed, like a pan with a loose lid, so heating the crankcase and the water which it contains will also raise the dew point. What is needed is to remove the water vapour like this or with Achim’s homemade version.
As for ruptured oil coolers, I suppose that’s a fair point in extreme cold, with a pilot who doesn’t monitor the operation of the oil pressure release valve, or with the incorrect grade of oil. I’ve never heard of such a problem with multigrade oil.
Incidentally, I once tested oils commonly used for cleaning and preserving guns by spraying steel plates and leaving them outside to rust. WD40 performed so well in that test that I’m inclined to say that oil viscosity is of secondary importance for long term corrosion protection.
Jacko wrote:
The crankcase is somewhat closed, like a pan with a loose lid,
It has a breather tube that directly link the outside air with the internals of the engine. The only thing could be circulation of hot air inside maybe? I would think normal variation of atmospheric pressure and a heater element causing convective flows would fix that though.
Picking up an old thread… What % of people fly at all in the winter months? Even the most casual look at FR24 shows that GA activity simply plummets – I reckon to around 10-20%. The homebuilt activity in particular seems to have dropped to almost nothing.
I have an excuse at least right now: TKS being installed 
My excuse for not flying our Jodel this winter is that we’ve delayed final assembly after major wing work due to the hangar temperature.
I flew a rented aircraft in November/December, and will probably rent again this month.
If I had instant access, I’d be flying a lot on good days, but renting means last-minute booking is sometimes impossible, and the weather forecast 2 days ahead is often inaccurate for the available daylight hours.
I fly during the winter as well. But the main reasons for the hours to rapidly decrease is weather and runway conditions. I operate at some smaller grass strips that tend to be muddy when the temps are close to zero for extended periods.
I couldn’t copy the YT url when I posted above from myNexus.
I would still like to fly as much as I do in summer, assuming the weather agrees. Unfortunately I’ve only been up three times since November, but all three times were on cloudless, crystal clear days. The last two were with temperatures a few degrees below freezing. The only problem I’ve found on these last two occasions is that ice likes to form on the wings after pulling the aircraft out of the hangar.
Peter, down here on the Scottish riviera, we get some splendid flying weather in winter. Runway condition is never a problem (with suitable tyre pressure), but the days are short.
So, if we arbitrarily define “winter” as the five months from November to March (rather than the 12 months during which we’ve been known to light a living room fire), the average flying time is about a quarter of the annual total.
I have over the past week been flying in areas where the weather was -6 to -27 C. I have never really flown and operated an aircraft in these conditions but it went quite well.
It certainly focuses the mind on hangars, batteries and avionics but I was surprised how robust the aircraft was.
Also landing on snow contaminated runways was a fairly new experience.
People in the Midwest of the US must cope as they fly in the winter all the time. The circuit traffic in -20 weather CAVOK was astonishing.
I wonder whether was are a little too conservative over here regarding broad flying weather.
I keep flying taking advantage of the ridge flying day and very occasional wave day. That is when said ridge doesn’t create orographic cloud. I also try to keep other member current from the back seat.
