Manufacturers have addressed many cooling system problems, but regular maintenance is still important
Heat is one thing diesel engines produce in abundance. The role of the engine and truck design engineer is to take that heat and do something useful with as much of it as possible and get rid of the rest in the most efficient way.
The heat of combustion in diesels is roughly divided three ways. One third produces useful power. Another third goes out through the exhaust system, and the final portion needs to be taken out by the cooling system. Note the portion that goes out with the exhaust. Now remember when EGR was first introduced, and engineers started taking some of those heated exhaust gases and returning them to the engine.
Engineers, of course, understood what was happening, so it was no surprise that cooling systems would be stressed. As a result, cooling systems were beefed up, but in many cases, not enough. It was when the first EGR-equipped trucks went into service that we started hearing stories of melted plastic parts from never-before-seen underhood temperatures. Thankfully, such horror stories are, by and large, a thing of the past.
Truck manufacturers and fleet managers have done an excellent job keeping problems in check, but many of the remedies have increased costs and some are costing fuel mileage. Design engineers have found ways to better manage the airflow through the radiator and over the engine, but underhood temperatures are still high and components are still stressed. For example, when fan clutches were first introduced, they ran only 3% or 4% of the time. Now they’re running as much as 80% of the time. Fan clutches are certainly better now with higher quality steel in the shafts and better bearings, but emphasis must still be placed on system maintenance. It is the case that even a minor reduction in cooling system function can cause a diesel engine to self-destruct.
While designs have improved, cooling systems are still too often overlooked during routine PM inspections. Darry Stuart, president and CEO of DWS Fleet Management Service, says, “Industry-wide, maintenance is not being performed on cooling systems as it should be. For example, I find upwards of half of the radiator caps in service are defective. They need to be checked during PM inspections and replaced when necessary.”
Pressurize at every PM
Engineers from the National Automotive Radiator Service Association (NARSA) note that the mileage on a vehicle is not as big a factor in cooling system maintenance requirements as is the vehicle’s age. An aging vehicle has been exposed over time to environmental factors that can harm a cooling system–– ocean air, road salt, debris and other chemicals tend to deteriorate the system.
The best way to check a system for small leaks is to pressurize it before making an inspection. In many cases a small leak might not even be noticed because of the high temperatures under the hood during operation. The leaked coolant simply evaporates as the truck goes down the road. The result could be an automatic shut down. Stuart says, “Fleets usually only want to pressurize a cooling system if they’ve experienced a problem. My goal is to do it before a problem occurs on the road. It doesn’t take a large leak to put a truck out of service.
“The question I always ask anyone objecting to pressurizing at every PM is, ‘When is the last time you added coolant to the radiator?’ You can get leaks even in new trucks. They usually occur in maintenance-related areas in the vehicle––hose clamps or, in some cases, small hoses that might not be checked routinely. The easiest way to determine if a fleet has cooling system issues is to look on the fuel island. If you see a drum or bucket marked ‘Coolant’ and it’s half full, there’s a problem.”
Even fleets that do pressurize cooling systems on a regular basis too often only pressurize to cap pressure. Stuart says, “I’ve always used 18 PSI, even when the industry was using 7 PSI or 8 PSI caps. Today systems are running as high as 16 PSI. Some people say 18 PSI is too much. My belief is, if something is going to leak, it’s better to have it leak in the shop than in the middle of Wyoming or Nebraska. Arctic Fox makes a great test device. Using shop air, set it to 18 PSI and in seconds the pressure in the system will be stabilized. Let it sit for awhile, then look for problems. After checking the truck for leaks, you can use the same test unit to check the cap.”
Clean systems are necessary
Even a cooling system free of leaks will fail if it is not cooling the engine effectively. For decades we’ve heard that cooling system problems caused at least 50% of all premature engine failures. That figure could change for the worst if cooling systems are not maintained to effectively control the added heat load inherent in EGR engines.
George Sturmon, chairman of ATRO Industries, says, “There are still coolant issues because some of the internal surface temperatures are so high that the coolant breaks down. Coolant problems are the result of high temperature differentials within the cooling system. The result is chemical dropout and coolant breakdown. No matter what new products or methods are used, there is one fact that stands out: cooling systems must be kept clean to do their job effectively.”
Fleets need an effective PM program to keep the cooling system clean. Because this can be labor intensive, it’s too often not done. Fleet managers should consider using cleaning filters that are used for a short time instead of normal coolant filters. Enviro-Cool, for example, has developed a spin-on cleaner/filter cartridge that chemically cleans the system while the truck is used in normal operations. The unit is left on the truck for three or four weeks. After that, the coolant is checked to ensure that dissolved solids are within OEM recommended levels. The cleaner/filter contains the chemistry needed to clean a cooling system as well as that needed to protect it against further corrosion.
Control the air flow
Since post-2002 engines, which are all equipped with EGR technology, don’t run any hotter than their earlier brethren, where does all the heat come from that raises underhood temperatures high enough to melt parts? Clearly, it’s from the air that has come through the radiator/air conditioning condenser/after cooler heat exchanger assembly and flows through the engine compartment. How about not having that air flow into the engine compartment? That’s exactly what Enviro-Cool has done with a new air management system designed to control underhood temperatures.
Sturmon says, “When EGR was first introduced in 2002, we began looking at ways to keep the hot air flow out of the engine compartment. As a result, we’ve developed a system that keeps underhood temperatures under 200 degrees F by removing heated radiator airflow through ducts in the hood and supplying cool air to the engine compartment by cowl air induction located in front of the windshield and vented by Venturi effect. We also believe that it results in a fuel savings of 7% to 9% because the system removes the fan, shroud and fan clutch.
Now eliminate the water
Evans Cooling Systems has had a waterless coolant under development for many years and just recently has introduced a new generation product. Water and water-based coolants have been the choice for cooling engines for many reasons. Water is cheap, available and a good heat conductor when it’s in its liquid state. However, if it vaporizes, it retains only 4% of its thermal conductivity.
Cooling systems are, therefore, designed to prevent water from vaporizing. These efforts result in coolant temperatures that are below (but still close) to the boiling point of water for the pressure of the system. But, as we’ve seen, there are localized spots at which boiling and coolant breakdown can occur.
Evans’ coolant, which it calls NPG+, contains no water, has a boiling point of 375 degrees F, high thermal conductivity and a 10-year shelf life. It is also called a lifetime coolant as long as it is not contaminated with any water. Because of the large separation between the coolant’s operating temperature and its boiling point, there will be no vapor in the cylinder head, no pump cavitation and no cylinder liner cavitation. According to Evans, a system designed to operate with water-based coolant, but using NPG+, will operate at conventional temperatures most of the time. Under conditions of particularly high thermal stress, the coolant will run warmer but the cooling system will not fail and metal temperatures will remain under control.
Since the radiator fan is a significant parasitic drag on the engine, consuming as much as 65 HP, keeping the fan off as much as possible saves significant amounts of fuel. Evans has found that an increase in fan-on temperature from about 205 degrees F to about 230 degrees F reduces fan-on time more than 50%––hence a fuel savings. For example, by using NPG+, Waste Management in Connecticut is realizing an 8% fuel savings during summer months when its fans would be operating the most and 5% during the winter.
What’s preventing widespread application of the technology? Mark Stone, Evan’s national sales manager, says, “The biggest obstacle we currently face is the lack of an endorsement from the OEMs. If nobody moves forward, nobody else has to respond. Engine manufacturers and truck OEMs are all working within the constraints of water-based coolants. Until somebody adapts our technology, there is no driving incentive for anyone else to do so either.”
If you use it efficiently, heat will move your trucks just as you want them to go, without problems and at a low cost. If you don’t control engine heat, it will simply destroy your engines.
Editor’s note: DWS Fleet Management Services provides experienced management to fleets on a limited-time basis. A former ASE-certified master technician, Darry Stuart’s extensive fleet management experience includes roles at numerous private, for-hire and leasing operations. His resume also includes 30 years as a member of the Technology & Maintenance Council (TMC) where he served as General Chairman of the Board of Directors. For more information, visit www.darrystuart.com.
