What about the freezing point of my coolant and the proper mix ratio? With a 50/50 ratio (Subaru recommended) of coolant to water -37 C / -35 F is the freezing point. Different coolants using different ratios will result in different freeze protection levels. Check the coolant product label for specific information as each coolant manufacturer utilizes additives that can affect freeze temperatures. If you live in an area where temperatures may go below these values, check with your Subaru service center for their recommendations on coolant dilution ratios.

What about coolant colors? Currently, there is no color standard. This means that if you have green coolant in your radiator, you should not necessarily buy green coolant to top off your radiator. In this situation, you can do two things if you do not know the specific coolant type:
1. Use a multi-compatible coolant. Some manufacturers have coolants that will work with many varieties of coolants. These products should also be silicate and phosphate free. Carefully read the manufacturer’s label for these details prior to purchasing.
2. Perform an engine flush and replace with new coolant. Note coolant manufacturer and type for future reference.

Are there compatibility issues with coolants? Yes. Some coolants are not designed to be used with other types. Ensure you read the product label for compatibility.

What about higher pressure radiator caps? Higher pressure radiator caps increase the boiling point of your coolant. Higher pressure = higher boiling point. Higher coolant pressures also transfer heat from the cylinder heads more efficiently. There have been several reported cases of higher pressure radiator caps causing ruptures in the endtanks on any OEM Subaru radiator. These should generally be reserved for aftermarket radiator users.