Whenever we have our oil debates it turns out that we are all doing fine with whatever we use. Maybe thats because we never run them long enough to find out its wrong, we'll never know.
Any thoughts anyone?
I had some thoughts.... I called them "The Thoughts Of Ralf"
1) The manufacturer lists an oil that is supplied on commercially favourable terms. Fiat (Alfa) used to own Fiat Lubfricanti (FL) who are now an independent oil supplier. They make Selenia. Ergo, Selenia is "recommended", as Fiat owned FL when our handbooks were printed. Probably it's still a good deal for Fiat.
2) The Selenia 20K is still up to the job. Fiat wouldn't specify oil that wasn't, no matter how cheap it was for them to buy.
3) The API rating is the most important thing. The v6 needs SG level oil, which is "chip fat oil" in terms of specification. You CANNOT BUY motor oil that does not meet this spec. Anything semi synthetic is SJ or SL. Synthetic is SM or SN. Miles (literally) better than the engine needs.
4) Research by Mobil showed that even a mineral oil is good for 20,000 kms if used at constant running speeds/operating temperatures. It's the cold starts, dusty climates, stop-start traffic (high temp and a lot of acceleration) that wears the oil.
So, change the oil regularly if you drive in challenging conditions. Half the recommended interval (6000 miles/10,000 kms) is plenty.
5) There is NO POINT sticking £50 of super-synthetic whizz-bang oil into a 155. The engine doesn't need it and the whole car is only worth a few times more than that. Use a cheaper but "quality" oil, such as 10W40 semi synthetic Castrol Magnatec or even the (slightly higher API rated) Halfords semi-synthetic (green can). Change it at 6000 miles and your engine will NEVER wear out.
My old beast has been fed on various 10W40 semi synthetics - Selenia, Shell Helix and Castrol Magnatec depending what I can get hold of. When I had the rocker covers off, the cams were perfect.
The motor has done 185,000 miles. I only change the oil at the recommended 12,000 mile intervals. The oil is fairly black by then but it still feels "springy" in my fingers, so has plenty of miles left in it.
It would seem that Alfa's recommended oil grade and change intervals seem to be spot on...