Coolant: Testing and Inspection

The percentage of ethylene glycol in the engine coolant should be checked periodically, when the engine coolant level is adjusted or the system drained and refilled. This test is done by using a refractometer. Refractometers test for the amount of ethylene glycol in a coolant mixture by measuring the speed of light as it passes through the fluid and are is affected by the specific gravity of the glycol.