Correct an existing coolant mixture
Use system capacity and a measured starting concentration to calculate one theoretical drain-and-refill. All percentages must use the same volume basis.
Worked example
A 10 L system measured at 30%, targeting 50% with 100% concentrate, requires replacing approximately 2.857 L of the existing mixture with concentrate. A 60% mixture targeting 50% using 0% water requires approximately 1.667 L replacement.
Assumptions and limits
The starting fluid is uniformly mixed, removed fluid has the measured concentration, and the system returns to its original total volume. This is not a model of repeated flushing, trapped pockets, or temperature-dependent measurement. Small measurement errors affect the answer; verify after circulation and cooling.
Use a measurement method appropriate to the exact coolant chemistry. Choose compatible fluid, target percentage, water type, and servicing procedure from the vehicle and product instructions. Do not open or drain a hot or pressurized cooling system. Follow disposal requirements for removed coolant.
How the calculation works
Replacement volume = capacity × (target − current) ÷ (replacement − current). A valid result lies between zero and the system capacity. Replacing fluid with an identical concentration cannot change the starting concentration.