Prestone just derates any coolant you got to prestone. In the older cummins, you couldn't run elc (hoat) coolant. It would cause gasket failer because it didn't have silicates. If it says to put the elc in, I would recommend CAT coolant (hoat). It comes premixed with distilled water. Great stuff, also last up to 6years where as most green coolant and almost any automotive elc (hoat) only lasts 2 years. In my 02 I run complete coolant, which is the green stuff that is good for 6 year with DCA in it (coolant is dyed blue). DCA helps keep scale down on the engine so if your cheap, you can use tap water as long as you maintain the DCA level.