It is no use to Shamus I suppose but I'd like to share a similar experience for the many Alfa owners that are looking to optimise the performance (but some also their bank account!):
-my garage put 5W30 in my 110k Alfa 156 1.8 TS
-I started reading, studying (I am a chemical engineer), getting informed. Also, checked some of my engine's reactions, this means: I heard some strident noise from the starter when I had the 5W30, I saw some stains below my car (for the first time...). Also I registered lesser fuel consumption (this was the only good point).
- I also called Alfa Romeo France and they confirmed me that the 10W40 is the good grade for my car
-this took me about a week. I then wrote to my garage, explained all this and I had them change the oil, at their expense, back to the standard 10W40.
Please also check the Selenia site, the answer is clear:
Selenia - tblAlfaRomeoAuto
They propose 10W40 for 156 TS motors (and as an alternative only) 5W40 but no 5W30.
I think the answer is unique:
1) Just put 10W40 to your Alfa TS engine, this is perfectly sufficient (only racing conditions would justify a 10W60)
2) when some differences exist with a garage, write them. Do not threaten, this is useless, even dangerous from a law point of view and, humanly speaking, not acceptable. But make them just resonsible of the possible damages. This works.