Water soluible oil added to the coolant will not harm the cooling 
system and it will do two things while there,  

  It will lubricate the water pump and other seals (headgaskets too).

  It will also dissapate heat in the cooling system.

  I've personally used this in VW's and in a car that I race.  The race 
car had a cooling problem and a person that had been around racing 
longer than dirt informed me about this product and it's usefullness.

  It did work in my two situations,longer lasting H2o pumps and cooling.

  My $00.02

-- 
   
  Kyle Wade
  Keeper of the Volks-Motorsports page
  Home Page - http://www.scruznet.com/~vwmaster