Engine Cleaner before Synthoil?

["Paul F. Levine" <paulevi@psd.k12.co.us>]

Hi,

I've heard it said that engine cleaner should be used before using 
synthetic oil for the first time. Any comments on this, recommended 
brands, potential harmful side effects?
TIA!

Also, the owners manual in my '87 5KCSTQW says basically to use 10W30 
winter and 20W50 summer. I was going to do this with the synths as well. 
I notice that Castrol and maybe others have oils like 5W50 which would  
seem to span the whole range of need. Any comment on using these wider 
range oils: ups/downs?

I live in Colorado where it can get to -20 or go up to 85 within a couple 
of days if not weeks.

Thanks again...

Paul