Ford 2013 C-MAX ENERGI Owner's Manual page 282

The coolant concentration should be maintained at 50%.
Note: For best results, coolant concentration should be tested with a
refractometer such as Rotunda tool ROB75240 available from your
dealer. Ford does not recommend the use of hydrometers or coolant test
strips for measuring coolant concentrations.
Note: It is very important to use prediluted coolant meeting the Ford
specification in order to avoid plugging the small coolant passageways.
Use of concentrated coolant and water may cause coolant passageway
plugging and void the warranty. See the technical specifications chart in
the Capacities and Specifications chapter.
Note: Automotive fluids are not interchangeable; do not use
coolant/antifreeze or windshield washer fluid outside of its specified
function and vehicle location.
Adding Coolant
WARNING: Do not add engine coolant when the engine is hot.
Steam and scalding liquids released from a hot cooling system
can burn you badly. Also, you can be burned if you spill coolant on hot
engine parts.
WARNING: Do not put engine coolant in the windshield washer
fluid container. If sprayed on the windshield, engine coolant
could make it difficult to see through the windshield.
WARNING: To reduce the risk of personal injury, make sure the
engine is cool before unscrewing the coolant pressure relief cap.
The cooling system is under pressure; steam and hot liquid can come
out forcefully when the cap is loosened slightly.
WARNING: Do not add coolant further than the MAX mark.
Note: Do not use stop leak pellets or cooling system sealants/additives
as they can cause damage to the cooling and/or heating systems. This
damage would not be covered under your vehicle's warranty.
2013 C-Max Full Hybrid (34h)
Owners Guide gf, 2nd Printing
USA (fus)
Maintenance 281