I have read the archives and I just cant figure out what oil to us?  I am new to this but I would like to know what oil to use in my 2.L Westy?  I live in NH and it gets down to -10F in the winter.  I need to keep it simple...What oil should I use....Winter/ Summer?  I am presently running 10W40 Castrol.  I plan to start running Mobil 1 Sythetic 15W50 on the next oil change.  

Any input would be great.   

Thanks, Jason   90 Westy