Why Do Diesel Engines Overheat?

In the United States, a semi-truck pulling 80,000 lbs of freight can cross deserts and climb mountains in a single trip. Heavy equipment works in the most severe environments. Diesel engines are required to perform, but sometimes things go wrong, and the engine overheats.

If an engine overheats, it can cause head gasket failures and cracked cylinder heads. Generally, the operating temperature of an engine should be between 190-220 degrees. Temperatures more than 190 – 220 degrees will put stress on the cylinder head, cylinder liners and engine block. The stress from overheating causes these parts to expand beyond the engine’s tolerances. This will lead to a blown head gasket and/or a warped or cracked cylinder head.

WATCH: Why do Diesel Engines Overheat

When a diesel engine overheats, and these failures occur it is costly; the repairs and downtime can easily be in the tens of thousands of dollars, so it is important to understand why overheating occurs and to know what to do about it.

Common Causes of Overheating

Even with the most stringent preventative maintenance plan, engines still overheat, causing thousands in damage and frustration for the repair technician. There are three common causes of overheating in a diesel engine:

Low Coolant Level or Coolant Loss

The coolant level should always be maintained at the manufacturer’s recommendation. Even when a technician ensures that the coolant level is where it should be, the harsh environment can cause damage. Continued loss of coolant may indicate external leaks around hoses, gaskets, radiator, water pump, thermostat, heater or freeze plugs. A cracked cylinder head will also cause coolant loss and is sometimes indicated by white, puffy smoke coming out of the exhaust.

Air Pockets in the Cooling System

Occasionally coolant is drained from the engine to make repairs or as part of your engine’s general maintenance. Air pockets may form when coolant is refilled. If the air pockets are not bled out of the cooling system prior to start up, the air pockets will cause the engine to overheat. The manufacturer’s procedures are essential when refilling the cooling system. Many vehicles have bleeder holes or valves that allow you to remove the air pockets. Ensuring there are no air pockets will help the diesel engine avoid damage and stay on the road.

Faulty Thermostat

If the thermostat is not opening and closing at the correct temperature, it will cause the engine to overheat. The radiator, water pump and clutch fan should be maintained per the manufacturer’s specification to avoid overheating. Contact your AFA Industries representative for replacement engine parts.

Methods to Bleed Air from the Cooling System

There are two other methods available for bleeding air from your cooling system. Some vehicles have bleeder valves specifically for this problem, located at the top or in front of the radiator. Open the valve and bleed the air trapped in the upper portion of the radiator. You can also jack up your vehicle from the front to bleed the air from the cooling system. This puts your radiator higher than the rest of the cooling system and helps force the air pockets closed. Keep the radiator cap loose to help the air move out during this process. The above recommendations are general guidelines and not intended to replace the OE manufacturer’s specific instructions for servicing or repairing their respective cooling systems.

How AFA Industries Can Help

Diesel repair technicians know that a strong preventative maintenance plan can keep the engine running smoothly. However, when a harsh environment causes damage, overheating can occur through no fault of the technician. When this happens, AFA Industries is here to help.

AFA Industries has a complete offering of engine parts for a variety of Caterpillar®, Cummins®, Detroit Diesel®, and Navistar® engines to rebuild most everything on the engine. Also available are Cylinder Components, Valve Train parts, Water and Oil pumps, Cooling System Components, Fuel System Components, and other engine parts to help you repair most components for these manufacturer’s engines. Consult the OE manufacturer’s service manual for your engine’s service requirements.

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