Similar with a 16 valver hydraulic cam followers motor that I've been tiddling with. The 10/40 is fine for the summer, but with the sharper mornings I rate a 5/40 which seemed fine with the 147 twinny we had. The one I mentioned I'd been tiddling with was not an Alfa, and the recommended for use, was a 5/30, which was way too thin for the summer, all 16 chattered like a worn sewing machine, so out it came, 10/40 was fine.
But, with these colder mornings the gal who owns it said she has a tapping sound on start up. Right enough, when I checked it myself, just one sticking, so we will have a rethink. In the meantime we have temporarily cured it by 1.making sure it's in the garage she has, and 2. covering the motor with a blanket at night!
(old Geezer I bin
) Leave a corner of said blanket sticking out of the part open bonnet to remind her, not to forget to remove it, before start up.
Nice little sixteen valver, but not an Alfa, we may try the 5/40 and see how that goes with the hydraulic take up.