Failure to properly maintain your cooling system is a leading cause of catastrophic diesel engine problems, accounting for approximately 40% of engine failures. The damage being done is difficult to see until it is too late. Liner cavitation and premature failure of the head gasket, water pump, radiator and other critical components occurs within the confines of the cooling system.
"Neglect of coolant maintenance happens all too often and most failures related to the coolant are very preventable," says Jared Parsons, Caterpillar Fluids Engineer. "As diesel engine technology advances, greater stresses are being placed on the cooling system. EGR coolers put a greater thermal stress on the coolant and can cause breakdown of the glycol."
Diesel exhaust fluid (DEF)/Selective Catalytic Reduction (SCR) systems, which are starting to come online in the on-road truck market, often use coolant to heat the DEF tank and thaw frozen fluid. "The additional mini-fuel system that is used in many engines today for active regeneration to burn off soot from DEFs can also include a cooling circuit for those components," says Parsons. "All these new technologies create new opportunities for problems to occur within the coolant and cooling system."
Randy Bushelli, customer support service and training manager, Volvo Construction Equipment, adds, "Today's engines use special alloys, seals and ceramics because of the higher peak cylinder pressures, injection pressures and heat that the engine produces. This requires more out of the cooling system than ever before."
It's difficult to assess the leading cause of cooling system failure. "Of all of the fluids on a piece of construction equipment or truck, probably the least understood is the coolant," says Stede Granger, OEM technical manager for Shell Lubricants.
One of the primary functions of coolant is to regulate heat within the cylinder head and engine block. It does this by picking up heat and transferring it to the radiator. It also protects against freezing and boiling, and corrosion and pitting of cylinder liners and the engine block.
In the U.S., there are basically two major types of coolant: fully formulated conventional silicate coolant and extended-life coolant (ELC). It's important to understand which type of coolant is used in your equipment.
"You have to know what type of coolant is in your engine and then maintain it the appropriate way," says Granger.
Conventional coolants are typically formulated with ethylene glycol base fluid mixed 50/50 with water. Water helps to enhance heat transfer, while ethylene glycol is the freeze point protector. The freeze point needs to be adequately set for the lowest possible temperature the equipment will encounter.
But more glycol doesn't necessarily translate into a lower freeze point. Once you get past approximately 70% glycol mixed with water, the freeze point actually starts going back the other way.
Water alone is not acceptable either. "If customers use water instead of coolant, it causes the cooling system to corrode," explains Yukiyasu Endou, director technical service, Komatsu America Corp. "If coolant is not available and water is the only option, we recommend water from a water tap with a corrosion resistor."
"When you use water that has a lot of minerals in it, you can actually be plating out some of those minerals on the heat transfer surfaces," Granger points out. Premixed coolants, which use demineralized water, ensure the product you are adding is at a 50/50 ratio.
It's important to maintain that proper balance. "Too high [a glycol concentration] and you can have issues with pumpability due to high coolant viscosity, as well as overheating, because glycol is a much poorer heat transfer fluid than water," Parsons explains. "Too low and you can have issues with coolant boiling in engine hot spots, such as turbos, cylinder heads and EGR coolers, leading to cavitation damage or cracking due to thermal stress. Also, when you over-dilute your coolant, you dilute the corrosion inhibitors, as well as the glycol."