How to Calculate the Concentration of Coolant in a Car

The proper coolant level in a car keeps the cooling system from overheating in the summer and from freezing in the winter. Equally importantly, the coolant retards rust and corrosion in the engine and radiator and lubricates the water pump and other parts. Periodically, you'll need to check the concentration level to be sure it is effectively doing its job. Here's how calculate and adjust the proper concentration.

Difficulty: Moderately Easy

Instructions

1. Drain and flush the cooling system to begin with the proper ratio of coolant to water in the system.

2. Check the capacity of your cooling system in your owner's manual to calculate the amount of coolant to add. In most cases, manufacturers recommend a 50-percent coolant concentration. In areas of extreme weather conditions, you can go as high as a 70-percent concentration, but never higher.

3. Add the required amount of coolant to the radiator (see link in Resources). Fill the radiator with clean water. Run the engine until it warms up, then turn it off and top off the radiator with more water.

4. Adjust the coolant level periodically by checking it with a refractometer. Temperature affects the coolant reading, and you can calibrate this instrument to accurately calculate the level over a wide range of temperatures.

Tips & Warnings

• The refractometer is an expensive instrument, so you may want to have the coolant level checked at a reliable repair shop that uses this diagnostic tool.
• The most common way to test the coolant level is with a hydrometer, which measures the specific gravity of the solution. However, temperature greatly affects specific gravity and will often result in an inaccurate reading.

Resources

• Chart for adding coolant.