AO Platinum Member
Join Date: Feb 2002
Location: The land that Time forgot
Re: dealer's choice of oil etc
An oil that's thicker will make the engine smoother and quieter as the oil itself damps out some of the sound. Obviously a VERY thick oil will trash your engine, as it's too thick to move around the pipes and oilways quickly enough, so always use the right grade for your car.
Oils from different manufacturers have different characteristics, even if they are nominaly the same grade. Selenia 10W40 seems part-way between a 5W40 and a 10W40 to me. Shell Helix and Castrol Magnatec seem a teeny bit thicker.
Dealerships (espcially those belonging to multiple chains) negotiate their own oil deals so you'll get whatever oil brand they use in the workshop. That may even change over time.
As long as it's the same grade and rating as Alfa recommends then that's okay. Your engine is more at risk from running low of oil or from using a seriously wrong grade, rather than because it has Castrol in it instead of Shell (etc.).
5W40 instead of 10W40 seems like a case of they ran out of 10W40...
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