Are you in a unheated hangar
You mean like 99% of all GA aircraft owners? Are you the 1% that has a heated hangar? 
Even if I had a heated hanger, I would still use X/C in winter because I can’t pre-heat well when going places. Based on everything I have read and know, AS50 is not a good choice. PAO oil (see Mobil A1) was a flop and ruined engines in large numbers. Using 50% PAO instead of 100% can’t suddenly make it a good oil for our engines. If you want multi-viscosity but no PAO, Philips X/C is the only choice today.
Of course most hangars are unheated But it’s the combination of living in a very cold-winter location (Norway for example) and an unheated hangar. For this reason, hangars in very cold places tend to be heated, otherwise you can’t get the ice off the aircraft easily.
I guess I am fortunate to be based in the southern UK which has been down to -8C (IME) but this is very rare. Normally one hovers around +5C.
Achim: I get my oil from oil-store.com Then will have it shipped here by ship. 80cts a pound. They were closed so could not get an exact price.
Peter I used to be in a heated hangar. I would still preheat depending.
As Achim mentioned what if your away and have straight wt 100? I preheat normally when the temps are in the 50s-60s (10-17c) and havent used the airplane in 2 weeks.
Reason for multi wt., if I cant get preheat and the temp is low 40s (6c) but above 32 (0) I would, if pressed start up. However only with multigrade but not with 100. I would never start without preheat below 32 (0) multi or not. I like to see the oil pressure move up within 5 sec of turning the key.Thats even more important if I hadnt flown in more than 2 weeks. Just being a bit anal. But my last engine went 300hrs past TBO.
Result of my first oil analysis where I used Phillips XC 20W/50 and CamGuard. It’s the second time I use this oil combination, but I skipped the previous oil analysis, since I only do oil analysis every other oil change. Many elements are at an all time low, albeit this oil change was also a short run (30 hours), however it was still 4.5 months in between. I did not had any cylinder work done as the comment suggest. Engine has 1600 hrs. The result suggests that CamGuard appears to have better protective qualities.
Here is mine; just arrived
The calcium is the Camguard tracer.
Did something happen on yours between 2006 and 2013? There was almost no flying during that time. Maybe oil analysis was not being done, because with so little flying one would normally see a massive amount of iron(rust) and other wear elsewhere.
Among Cirrus Pilots (COPA) Camguard is the # 1 additive. I switched from using W15/50 to D100+Camguard. It seems to be the only additive that really makes a difference.
Did something happen on yours between 2006 and 2013?
Nothing happened. Previous owner must not have done oil analysis, or used a different oil lab. Engine was overhauled in 2005, so analysis prior to this year are not relevant.
What is the tracer (Calcium) good for?
I think they put it in so they can tell you are using it
I once had Blackstone swap my sample for somebody else’s and it came to light because the figures looked totally wrong. It was confirmed by the other one having the calcium but that pilot was not using Camguard.
However it also came to light because I had sent a sample of the same oil to Intertek (UK) whose results have always tracked Blackstone’s closely, but this time they didn’t.
A third lab I used, Avlab in the USA, produced results which were way off the other two. OK on their own, but obviously using a different process. The details are all here on EuroGA – search for the names of the firms. I spent a lot of money getting that data, from 2 or even 3 labs each time.
Nowadays I use just Blackstone.
