Preliminary Information
PRELIMINARY INFORMATIONWARNING: As long as there is pressure in the cooling system, the temperature can be considerably higher than the boiling temperature of the solution in the radiator, without causing the solution to boil. Removal of the surge tank cap while the engine is hot and pressure is high will cause the solution to boil instantaneously possibly with explosive force spewing the solution over engine, fenders and person removing the cap. Under some conditions the ethylene glycol in engine coolant is combustible.
Before draining and recovering the cooling system, inspect the system. Perform any service needed to ensure that the system is clean, does not leak and is in proper working order.
Some coolant manufacturers mix other types of glycol into their coolant formulations. Propylene glycol is the most common new ingredient. However, do not use propylene glycol in GM vehicles that were manufactured with Dex-Cool coolant.
A hydrometer does not always provide a correct measurement of freeze protection when anything other than ethylene glycol and water is being tested. The degree of inaccuracy varies depending on the proportion of other glycols present in the coolant.
Hydrometers test the amount of glycol in a mixture by measuring the specific gravity of the mixture: the more ethylene glycol, the higher the float balls go, and the better the freeze protection. Because ethylene glycol and propylene glycol do not have the same specific gravities, hydrometer readings of mixtures containing propylene glycol give incorrect values. Use a refractometer when you test coolant. Refractometers test the amount of glycol in a coolant mixture by measuring the speed of light as the light passes through the fluid, and is not affected by the specific gravity of the glycol.