Chapter 5 N40469 How to check the specific gravity of the coolant For mixtures which contain inhibited ethylene glycol: 1. Operate the engine until it is warm enough to open the thermostat. Continue to run the engine until the coolant has circulated the cooling system. 2. Stop the engine. 3. Allow the engine to cool until the temperature of the coolant is below 60 O C (140 O F). Warning! Do not drain the coolant while the engine is still hot and the system is under pressure because dangerous hot coolant can be discharged. 4. Remove the filler cap of the cooling system. Specific gravity chart 4.
Drain some coolant from the cooling system into A = Percentage antifreeze by volume B = Mixture temperature in O F C = Specific gravity D = Mixture temperature in O C a suitable container. 4. Use a special coolant hydrometer that will check the temperature and the specific gravity of the coolant, follow the manufacturer’s instructions. Note: If a special coolant hydrometer is not available, put a hydrometer and a separate thermometer into the antifreeze mixture and check the readings on both instruments. Compare the readings with the chart. 7. Adjust the strength of the mixture as necessary. Note:
If it is necessary to fill or replenish the coolant system in service, mix the coolant to the correct strength before it is added to the coolant system. Perkins antifreeze with a concentration of 50% will give protection against frost to a temperature of -35 O C (-31 O F). It will also give protection against corrosion. This is especially important when there are aluminium components in the coolant circuit. Page 28