I use Castrol 20W50, petroleum based (nonsynthetic).  I change the oil 
every 3000 miles, just as I always have for all my vehicles.  I can't 
imagine how synthetic could improve on that.  I notice that most 
manufacturers specify that oil should be changed at the recommended 
interval, and that less often than that voids the warranty, whether the 
oil used is synthetic or not.  David McNeely

On Mon, Jan 11, 2010 at 1:46 PM, Stephen Cebula wrote:

> What motor oils you you all use out there?  A friend of mine keeps 
> pushing synthetic oil.  He's a Ford man, and not familiar with 
> Vanagons.  What's the rap on that?
> Steve