I want to top-up my coolant level a bit before I have my garage do a flush-n-fill in a couple more months.
Prestone sells "Prestone 50/50 antifreeze and coolant" which they state is "compatible with any antifreeze/ coolant - regardless of color - for use in all makes or model of cars and light duty trucks." It is "demineralized water and ethylene glycol" with "no nitrates or silicates."
What do you think?

 

a cup or 2 of distilled water will do just fine

 

I wouldn't mix Prestone or any other type of coolant with the Dexcool that comes with the Vantage, but that's just me.

 

Mixing coolant types can cause gelling. If you just need a top off use distilled water. Since your car is a 2006 your car is already past due for a change if it hasn't been done. If you have a DB9, its surprisingly easy to do a coolant change. Search this forum for my DYI write up, if you feel brave.