The S3 was listed mainly with 10W40, with 15W50 being an option. Start it up on 10W60 and you will likely be well about the temp the 10W is measured at. Ie, the 50W oil is what can be used when temps are very hot.
Its your car, but tappets pumping up from using thicker oil is a known problem on some cars. Personally I wouldn't risk it as it would seem that at best all you are doing is masking a problem with the actual higher oil pressure being irrelevant.
strange that the S3 would have a 10w/40 and the S2 10w/50. Almost the same design no?
I know the S3 has the oil jets to cool the pistons but the S2 doesn't have this feature.
Maybe because of the small jets.
I know I'm not masking an issue because the engine was just rebuilt.
But this was in the summer when I was testing it.
If you had a roadside temperature of 55 degrees and stuck in traffic how would your oil cope? What would you use?
Now it's winter here I agree the 15w/50 should be just fine.
Some have issues with tappets at start up. Rattling away until they pump up.
Never had this issue with either 5w/15w/20w oils.
Only issue I had was before the rebuild was ticking when oil got hot. I had destroyed tappets!
All these were changed with the cams. Also a couple of newish cam boxes added. etc etc.
How evident is the issue of 'pump up' of tappets? Wouldn't you notice a huge loss in compression?