How do I add make up coolant?
When you are adding make-up coolant to the sump never add straight water or coolant concentrate to the sump. Doing this will throw off the concentration of the coolant mixture. If the coolant mix in the sump is too concentrated then add a make-up coolant mix that is less concentrated and if the coolant mix in the sump is not concentrated enough then add a make-up coolant mix that is more concentrated. A good rule of thumb is the 15 principle: if you initially charge with a 20:1 mix and the coolant in the sump is now too concentrated then add a 35:1 mix. After adding makeup run the sump for a few minutes before taking another refractometer reading. Keep repeating these steps until you have reached the initial 20:1 concentration.