We have learned:
Sierra:
a) will work in a Vanagon
b) is propylene glycol based
c) is phosphate free

Prestone 5/100:
a) will work in a Vanagon
b) is ethylene glycol based
c) is phosphate free

Both are about $7.00/gal. HOWEVER, Prestone 5/100 is ORANGE. Yes it's 
true. This is done purposefully for it CANNOT TOUCH ANY OTHER TYPE OF 
COOLANT! If this touching occurs then a jelly-like substance will form. 
The label says that the system must be thoroughly flushed of all other 
types of coolant before Prestone 5/100 (5 years 100K miles) can be 
installed.
My beef against this brand is that theoretically you should carry TWO 
gallons with you, in case you pop a hose or otherwise drain your coolant 
loop, for the Prestone 5/100 CANNOT TOUCH ANY OTHER TYPE OF COOLANT. So 
if you did bust a hose, and had no access to this exact brand, then you 
must THOROUGHLY flush your coolant loop before installing anything else.

I'm putting in the Sierra, I understand the propylene glycol is not as 
efficient as ethylene glycol at transferring heat, but I would sure be 
hot if I could not find any in Smalltown Texas with a coolant leak. 

Mark B. Magee
87GL 76K
Galveston