Coolant System Maintenance for Diesel Engines

The coolant system is a critical part of your diesel engine – perhaps more than you may realize. However, some operators only pay attention to the coolant system when a hose leaks or the engine overheats. But neglecting the coolant system can lead to total engine failure.

Purpose of the Coolant System

The coolant system is filled with a solution known as coolant, antifreeze, or radiator fluid. This solution performs several critical functions: 

• Transfers heat from the engine to the radiator, which dissipates heat into the surrounding air.  
• Prevents the engine from freezing in the winter and overheating in the summer.
• Protects the coolant system from corrosion. 
• Protects the engine from cylinder wall cavitation, which can occur in diesel engines with replaceable cylinder liners (or wet sleeves) fitted into the engine block. A cylinder liner separates the reciprocating piston inside the liner from the heat-dissipating coolant outside the liner. The movement of the piston vibrates the cylinder liner which can form air bubbles in the coolant. When the bubbles burst, they create a high-pressure stream of coolant that can erode the cylinder liner, just like moving water erodes rock. The cavities produced by this erosion can eat through the cylinder liner. This will allow oil and coolant to mix, resulting in engine failure.

Types of Coolant

All coolants consist of three main ingredients: A base of ethylene glycol (EG) or propylene glycol (PG), water, and additives to inhibit corrosion and cylinder liner cavitation. That sounds simple, but any engine operator knows there are many types of coolant on the market. Let’s take a look at what’s available.

First of all, is there any difference between an EG-based or PG-based coolant? No, not in terms of performance. Water solutions of EG and PG have comparable freezing and boiling points, so both chemicals protect your engine from overheating or freezing. However, EG is toxic whereas PG is non-toxic. PG is environmentally-friendly and safe around humans, animals, and food products. PG-based coolants are often used in ag applications. 

Coolants are also labeled as IAT (inorganic acid technology), OAT (organic acid technology), or HOAT (hybrid organic acid technology). Here is what you need to know about each of these choices.

Inorganic acid technology (IAT) is the conventional coolant often dyed green and containing silicate and nitrite additives. Silicate increases the boiling point and lowers the freezing point of the antifreeze solution. It also coats the metallic parts of your coolant system to inhibit corrosion. Nitrites form a tough oxide layer on the outside of the cylinder liner to prevent cavitation. Over time, the protective additives will be depleted. Then the coolant system should be flushed and fresh coolant added. 

Organic acid technology (OAT) uses organic acids as rust inhibitors and is often dyed orange. These inhibitors attach to the metal surface of the cylinder liner by electrochemical means to prevent corrosion. OAT coolant is offered with nitrates (NOAT) or nitrate free. OAT coolant overcomes some issues associated with conventional coolant. For example, the additives in OAT coolants deplete very slowly. If an engine is properly maintained, extended-life OAT coolants can last for 12,000 hours of running time. 

Hybrid OAT technology (HOAT) is often dyed yellow. It combines the anti-corrosion benefits of IAT and OAT coolants, using silicates, nitrites, and organic acid as rust inhibitors. HOAT coolants offer long-lasting service life and engine protection.

Always refer to the engine OEM specifications when choosing a proper coolant for your diesel engine.

Coolant System Maintenance

Any engine will benefit from good coolant system maintenance. Here are a few pointers to help you maintain an optimal system.

Fluid maintenance

• Coolant will degrade over time. If you do not know if your coolant has degraded in storage, buy a fresh supply.

• Refill or flush the coolant system as needed. Experts have various opinions about how often you should flush the system, so refer to your OEM specifications.

• Use the proper coolant.

System maintenance

• Keep your coolant system clean.

• • • Remove dirt and debris from the radiator core area.
    • Ensure proper airflow through the fins.
    • Use compressed air to remove dust and light dirt.
    • If dealing with an oil film, use a cleaning solution and water at low pressure.

• Be sure that the charge air cooler fins are clean (if applicable).

• Replace damaged parts.

• Inspect coolant hoses.

• • Check the radiator hoses, EGR hoses, cab heater hoses, thermostat bypass hoses, and oil cooler hoses.
  • Look for cracks, cuts, or bulges.
  • Hoses can harden with age and heat. Replace a hose if it is not pliable.
  • Ensure all hose clamps are secure.

• Check the fan and belt.

• • • Replace the belt if it is cracked or frayed.
    • Be sure the belt tensioner is maintaining proper tension.
    • Check the fan blade for any cracks.

• Check the water pump for leaks or traces of white deposits indicating a leak.

• Confirm that the thermostat maintains a proper operating temperature.
• Ensure that the block heater is operating properly (if applicable).

Even though an engine’s coolant system doesn’t seem as critical as fuel and oil, ignoring it can be costly. Many engine failures are the result of neglected coolant systems. But proper maintenance and routine inspections of the coolant system will keep your diesel running at its best.

Visit our Parts & Accessories page to purchase coolant or maintenance supplies.