Given that I was measuring 110C oil temperatures in the vicinity of the add/full marks on the dipstick of my L67 at freezing temperatures this year (3.2HTHS 5W30 FWIW), after 20km on the highway, I'd not play that game should you have any likelihood of sitting on the highway for 15-20 minutes.
Member 3800series (IIRC) has been using 20s in his 3800.
If I could get a 20W20 locally, with an HTHS in the 2.9-3.0, I'd probably have at it 'though...GMan's UOAs of 20W20 valvoline (in Chrislyer Hemi)were good.
Considering I have a 3800 and live near Buffalo NY, I have never heard my car sound rough using PYB 5/10w30 even during the worst winters. I try to time my OCI so I use the thinner oils from Dec-Mar and then go back to 10w30 for the rest of the year. 232k with no oil burning, 27-28 average mpg right now and the engine is not the weak spot, the transmission is. If it were me, I wouldn't bother with the 0w20 stuff.
When you consider that early dino 5W-30s generally sheared to 5W-20s during a typical OCI, I'd think that a shear-resistant 5W-20 would probably be okay.
What do you hope to gain, though?
You won't see easier winter starts unless it gets a whole lot colder on your side of the river than it does here and you won't see any measurable improvement in fuel economy.
Well I have in my Bummer and I know some guys with GM V8s who have but we have oil pressure gauges so we new what the operational viscosity was at all times.
That said, I'm sure you can especially M1 with it's slightly higher 2.7cP HTHSV. And how much viscosity difference is there in service between that and a cheap 5W-30 of 15 or more years ago which is all GM spec's for it and that's for the hotest possible conditions in the summer?
Since you're into motoroil why not install an OP gauge, it'll only cost you 40 bucks or so for the gauge and sensor. I'm sure a local speed shop wouldn't charge much for labor if you buy the gauge from them if you don't want to do the job yourself. You could likely include an oil temp gauge for not much more for the complete package.
The thing about oil gauges, it's always nice when you conduct these experiments to know what your actual minimum OP was and highest OT and how the car was driven at the time.
BTW, years ago I posted an experiment (l think it was an SAE paper actually) where they ran a custom fully formulated 5 weight motoroil (IIRC the HTHSV was 1.7cP) in a V6 GM pick-up for something like 20,000 miles on the street including some WOT acceleration from time to time. They then tore the engine down and everything was still to spec'.
If I can dig up again I'll post it.
I think this obsession with 0W oils is getting a bit out of hand in mild climates especially for engines where the oil is not specified. Northern US or Canada is something else.
So if 901Memphis said 5W-20 instead you guys would be okay with that?
The issue is about running a 2.6-2.7cP HTHSV motor oil and has nothing to do with the oils winter rating.
To the back of the class you go.
The 3.1 and 3.4 will last as long as any other engine with proper maintenance. The biggest issue with them is lower intake and head gasket failure, and you can get replacement gaskets that are better quality than factory from Fel-Pro. I've seen several run well into the 290K range. That being said, they are far from my favorite engine. I'd rather have the 3800. To say they aren't long-lasting is an incorrect statement though. As far as oil, I'd say a 0W-20 or 5W-20 would be ok, although I'd probably run a 5W-30 conventional. Any synthetic is overkill for these. If you want to run it however, it's your car and money buying the oil, and I know from your post you are a synthetic user. If you decide to try the 0W-20, let us know how it goes.
Already had the engine replaced due to intake gasket/overheating problems, with a used engine with less miles (approx 100k on it) they put the new gaskets on the engine when they swapped it, so hopefully it doesn't happen again.
I am already using PU 5w30 SN (the Pre Pure Plus formula), which should be about as good a winter 5w30 as any ( Viscosity @ -30ºC mPa s (cP) (ASTM D5293) 3,827 - max 6,600 per PQIA.
I was more or less curious as to other member success, since i do short trip frequently and the oil never gets up to temperature unless its the weekend.