off the back of the "what oil" thread a few months back i changed my engine oil last week and opted to try 20w50 mineral. engine didnt seem much quieter at all (not that its that noisey anyway) but did notice a slight knocking that sounded much like piston small end when started from cold. it only lasted a short time (20 secs) and would go when rev'd.
was slugish to turn over when starting as well at these times.
stupid idea putting 20 grade oil in when outside temps where around the zero mark!
it has since yesterday been drained and filled with 10w40 semi! seems much free'er reving i have noticed.

This is the reason why I always pour 0W-xx in mine, year round. In spite of global warming and at least my fervent wishes that it gets warmer - England is still quite cold in winter.

If one really does want the quiet running of a xxW-40 a great compromise is a 0W-40 oil, it is a bit like eating the cake and still keeping it.

Never understood the need for xxW-50 oil, unless it is for extreme racing, extreme desert use or an exceptionally worn engine. It just looses lots of power and increases fuel consumption for no discernible benefit.

I run my 4.6 (Lucas Engine Management) on 0W-30 and it is easy to start in the cold, gives full power and the best MPG I can hope for whilst getting good protection of the oily bits. It could be argued that a 5W-30 would be just fine for England, and I would agree, I just like the idea of having the least damage done at cold starts.


Oil viscosity primer:
The 0W- part is the viscosity at "Winter temperatures" and the lower the number the runnier it is.
The -40 part is for the viscosity at 100° C, again the lower the number the runnier it is.