Exhaust emissions control technology has substantially increased the heat rejection requirements of heavy-duty diesels. OEMs have responded by increasing the pressure of engine cooling systems. This has contributed to higher underhood temperatures, to the detriment of components located in this hostile environment—a situation that has been addressed by some new design technology.
Demands increase
It has also stepped up the importance of cooling system maintenance since studies still find that more than half of the engine problems experienced by heavy-duty diesels can be attributed to troubles with their cooling systems. Darry Stuart, president and CEO of DWS Fleet Management Services, says, “The rules haven’t changed much, but closely following the rules is more important today than before because of the extra heat from EGR engines that must be dissipated. System pressures have risen from about 10 psi to as much as 18 psi. We may even see 20 psi in the future.”
According to experts from The International Heat Transfer Association, the mileage on a vehicle is not as big a factor in the maintenance requirements of a cooling system as is the vehicle’s age. This makes older vehicles prime candidates for cooling system troubles. If a system isn’t in good repair, just idling in traffic can cause an engine to overheat, even when operating in a cold, winter environment.
Hardware checks
It was because of the need to increase boiling points that operating pressures of cooling systems have been raised—in some cases quite dramatically—and fan-on time has gone from about 5% to as much as 85%. The bottom line is that a couple of items might need to be added to a fleet’s PM check list.
Many radiator caps that are causing problems might not be older, in-service items. There seems to be even a problem with many replacement parts coming onto the market. Stuart says, “I find that a third of new caps are not able to hold the right pressure. Most fleets, unfortunately, don’t check pressure caps either when they’re new or when they’re doing PMs. Even fleets that do pressure check cooling systems often only do it when they have a leak. Systems should be checked at a minimum of 18 psi. Let it sit for at least 10 minutes to make sure here are no external or internal leaks.”
There is one area in which fleets have an opportunity to save a few dollars. Leaks from hoses and hose connections have been addressed in many cases by using relatively expensive silicone systems. That may no longer be necessary, as regular hoses have been substantially improved. Stuart says, “I was an early user of silicone hoses, but regular hoses today are much better than they’ve ever been and are working extremely well.”
The increase in fan-on-time is taking its toll on drive pulleys. According to Stuart, “V-belt grooves are wearing more rapidly on newer engines, and as a result, fans are not getting full grip of the drive belts.
The result is slippage. There are tools available that will measure groove wear and should be used regularly.
Coolants
Coolants are commonly placed into one of two general categories: conventional fully formulated or extended life products. The latter is further divided into either nitrated or non-nitrated. Long-life formulations, for the most part, do not contain nitrates, borates, phosphates or amines. They also don’t contain silicates that are normally found in fully formulated coolants.
The kind of product that is used is, of course, up to the fleet. Chevron’s Ulabarro says, “I’d say that 50% of the fleets are already using long-life products. Change is not an easy thing for any commercial operation, since technicians have been doing things the same way for many years. Fleets that are not using long-life coolants generally say that they are comfortable staying with the maintenance practices that are required and that they really don’t want to change.”
Fleets that have not changed from conventional coolants may run into some issues in the future because engines are going to be running even hotter than they are now. All fully formulated coolants contain silicates that form deposits on cooling system surfaces, which impede heat transfer from the coolant through the metal and out into the atmosphere.
Ulabarro says, “Those who are still on fully formulated coolants are probably going to see some issues with trucks running a bit hotter than they should. The downside of that is that the hotter a truck runs, the more stress is on the oil and on componentry in general, like seals.”
There are some fleet managers who consider all coolant formulations to offer long life. Stuart says, “I’ve been recycling antifreeze for 35 years. Take it out when you need to, then put it back in. The important part is to replace the supplemental coolant additives (SCAs) and measuring the nitrate levels during every B-level PM—anywhere from 25,000 to 45,000 miles, depending on what the fleet’s program might be. If you do that, you won’t have any cooling issues.”
A new concept
Using a radically new concept, EnviroCool has developed an air management system that replaces a truck’s normal cooling system and offers proven fuel savings. Claude Travis, a well-known industry consultant who specializes in fuel economy testing, says, “The EnviroCool Air Management System is a clear breakthrough in that it has been proven to offer a 7.5% improvement in fuel economy. I personally think we will see this system in wide use in years to come. My advice to fleet managers is to follow the progress of this project closely and plan on utilizing it in their fleets.”
George Sturmon, EnviroCool’s chairman, describes the company’s new Air Management System as eliminating all of the familiar components of the cooling system in front of the engine and replacing them with two separate parts.
The first portion is a coolant-to-air heat exchanger (similar in concept to a common radiator) combined with an integral plenum that incorporates several small electric blowers that turn the ram air coming through the radiator 90˚. This air then exits through the sides of the plenum into ducts on both sides of the engine’s hood.
At this point, the new system has eliminated the need for a bladed fan and its drive pulleys, thereby saving about 65 HP and increasing fuel economy by 7.5%. It has also eliminated the fan clutch, which has become a relatively high maintenance item on EGR engines since it now needs to run upwards of 85% of the time instead of less than 5% for pre-EGR engines. Sturmon says, “A bladed fan is a very inefficient device if it does not have a clear area behind it. If there’s anything behind it, something like an engine block, air pressure from the fan builds up. The result is that bladed fans in engine cooling systems run at less than 40% efficiency. That’s why truck manufacturers have had to make cooling fans bigger and stronger.”
The second part of the system is designed to control the temperature in the engine compartment. To do that, the new EnviroCool design uses cowl air induction similar in concept to that used on NASCAR vehicles. In such a system, air enters the engine compartment from just below the windshield and flows very rapidly through the engine compartment, efficiently sweeping heat out. Tests show that the air in the engine compartment is changed every 30 seconds.
Unfortunately, the industry still does not seem to recognize the importance of cooling system maintenance for the longevity of the vehicle. It’s a system that is too often neglected.
