1. Classifications of Coolant

1.2. Coolant pH

LO 11-04: Classify and describe the types, functions, and applications of diesel engine coolant.

 

Coolant pH

One major factor affecting the corrosion rate of the metals in an engine is the coolant’s pH level—that is, its alkaline or acidic chemical property. A material’s pH is measured on a scale of 0–14, with 7 being neutral. A coolant with a pH less than 7 is acidic, and a coolant with a pH more than 7 is alkaline. Coolant pH should be maintained between 8.5 and 10.5. Shifts in coolant pH affect the rate of corrosion of different metals Figure 29. If a coolant’s pH drops below 8.5, it becomes aggressive to ferrous metals (e.g., cast iron and steel), aluminum, copper, and brass. If it increases above 11, it becomes aggressive to aluminum and solder. Maintaining optimum pH in a coolant is a critical function of a supplemental coolant additive package that also contains DCA or SCA. Ethylene glycol antifreeze can become more acidic over time when exposed to air. Combustion gas leakage into coolant can also make it acidic. Overconcentration and overuse of a conditioner that contains pH buffers to make coolant alkaline cause coolant to become destructive to engine metal as well.

   Fig11_29

FIGURE 11-29: Depending on the coolant’s pH level, it can become corrosive to different types of metals.

 

  Technicians Tip  
  Too much of a good thing is bad. In the case of antifreeze, overconcentration can lead to engine overheating because antifreeze does not remove and release heat as quickly as water. Even though the cooling system temperature may be normal, the in-cylinder temperatures will be higher. Additionally, less heat is also released by the heater core and radiator, which can lead to engine overheating in some instances. One of the least intuitive but most important diagnostic tests to perform on overheating engines or engines with complaints about cold cab temperatures, when the heater core is not producing heat, is measuring the antifreeze concentration. Remember too that overconcentrating ethylene glycol antifreeze causes an increase rather than a decrease in the coolant’s freeze-point protection.  

 

  Technicians Tip  
  Ethylene glycol, which is the base from which the majority of antifreezes are made, is toxic. Less than 4 ounces (oz; 113 grams [g]) will kill a 150-lb person (68 kg). Because ethylene glycol is toxic, antifreeze made from this base is an environmental hazard and must be properly disposed of. Discarded antifreeze is typically picked up and recycled by licensed recyclers. And, in many jurisdictions, agreements for recycling shop waste, such as antifreeze, oil, and batteries, are required by law.  

 

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