Coolant: Description and Operation

DESCRIPTION
Some coolant manufacturers mix other types of glycol into their coolant formulations. Propylene glycol is the most common new ingredient. A hydrometer does not always provide a correct measurement of freeze protection when anything other than ethylene glycol and water is being teste The degree of inaccuracy varies depending on the proportion of other glycols present in the coolant.


MEASURING OPERATION
All new GM vehicles are produced with coolant the can be accurately measured with a hydrometer; however, when the type and quality of coolant being measured is unknown, such as a customer vehicle that has accumulated mileage, the use of a refractometer is recommended. Coolant testers J26568 (Centigrade Scale) or J 23688 (Fahrenheit Scale) can be used to check the antifreeze protection of the coolant. Make sure the refractometer markings are correct. Unless J26568 or J23688 has a provision for temperature correction, test the temperature at which J26568 or J 23688 is calibrated. If the coolant is warmer or cooler, the reading may be incorrect. Follow the manufacturers' directions on using J26568 or J 23688.

CIRCULATION OPERATION
In the Northstar cooling system, the water pump takes coolant from the radiator and passes the coolant through the thermostat on the inlet side of the water pump. The coolant enters the block at the rear of the engine from the water crossover, then the coolant is routed through the cylinder, heads back to the water crossover. At this point the coolant has four possible routes:
^ The radiator
^ The bypass
^ The heater core
^ The throttle body heater circuit