by Paul Abelson, technical editor
For years, I’ve been writing articles telling operators all the wondrous things that must be done to properly maintain a truck. As I look back, I wonder if someone paying attention to every word will actually have time to drive the truck. Sarcasm aside, I realize there’s a great deal to be done to keep trucks running, and anything relieving that burden can’t be all bad. Thankfully, several relatively new developments allow you to (almost) forget about maintaining your cooling system. They all have strengths and weaknesses, but when used according to manufacturers’ instructions, they all work well.
As this engine thermal cutaway shows, inside the water jacket, heat-stressed metal exceeds the thermal capacity of conventional coolant. Area A shows the coolant boils, forming a vapor barrier at the metal’s surface. This barrier acts as an insulator to prevent efficient heat transfer from the metal to the coolant, causing localized overheating and coolant vaporization. At Area B, Evans’ nonaqueous propylene glycol (NPG) coolant bathes the entire cooling jacket and significantly improves coolant surface effectiveness. Heat transfers more efficiently from the metal to the coolant. (Courtesy of Evans Cooling Systems.)
Before we get to new technologies, let’s review how a cooling system works
Coolant is a heat transfer medium. It absorbs waste combustion heat from the engine’s cylinders and heads, then carries it to the radiator. There, it gives up that heat to air flowing through the radiator. Water is an excellent medium for transferring heat, but water has some disadvantages. It freezes, and when frozen it expands with enough force to crack an engine block. It must be mixed with something to keep it from freezing. Water often carries minerals that can deposit inside the engine. The deposits insulate, making heat transfer uneven, causing hot spots. Water promotes rust. It can boil and vaporize under specific conditions inside an engine. It can then recondense with enough force to punch holes through cylinder liners after just a few thousand miles of driving.
To prevent these problems, ethylene glycol (EG) antifreeze and additional chemicals called “supplemental coolant additives,” or SCAs, are mixed with the water. This mixture corrects most of the problems, but creates a few others. That’s why we have to maintain cooling systems regularly.
Water can boil off, changing the concentration of the antifreeze. Coolant can leak. If refilled with water alone, antifreeze properties can degrade.
technologies designed to reduce maintenance
- programmed-release SCA systems
- organic acid technology (OAT) and
- extended-life coolants (ELCs)
- and non-aqueous propylene glycol (PG)
If there is too much SCA, harmful deposits form. They can clog coolant passages, abrade water pumps and attack seals and gaskets. Too little SCA and cylinder liners pit, scaly deposits form, water pumps aren’t lubricated, coolant foams, solder in the radiator degrades and the engine rusts inside. That’s why you need to check conventional coolant at every PM. You should keep at least one gallon of fully formulated coolant with you, so you won’t have to add just antifreeze or water on the road, or guess at the proper mixture. Fully formulated means it has the correct ratio of glycol antifreeze and demineralized water, and the right amount of SCAs. Whenever you need to top off your coolant, use fully formulated. An alternative is premix, a 50/50 mix of antifreeze and water without the additives. Don’t forget to check the SCAs as soon as practical.
No matter which system you use, you should carry one or two gallons. Not every truckstop has organic acid ELC, and even fewer have pure PG, although that number is growing.
Programmed release SCA systems are designed to minimize the attention needed by conventional (50-60 percent ethylene glycol plus water) coolants. If you have fully formulated coolant, SCAs are added as required. Timed-release systems have SCA pellets in a filter-like housing. The pellets are made to dissolve at a rate approximately the same as the rate SCAs are consumed.
A more precise system is Penray’s Need Release. Inside a filter-like housing, there are several chambers of SCAs, separated by metal membranes. When SCA levels fall to a pre-determined level, the membranes dissolve, one at a time, releasing just enough SCA to raise levels near the maximum allowable. SCAs deplete, and the process repeats, eliminating the need to check and add at every PM. Since they are conventional coolants, those using Need Release or timed-release SCAs should be changed every 200,000 miles.
Organic, or carbon-based acids replace SCAs in extended-life coolants made by Texaco and Valvoline’s Zerex division, and sold under a variety of private brands. Since these additives either do not deplete or deplete very slowly, organic acid technology ELCs need to be changed every 600,000 miles, provided a mid-life extender is added at 300,000 miles. Since there are no nitrite or molybdate SCAs, some operators feel they haven’t been fully protected against liner pitting with ELC coolants.
There was a heated discussion at a Technology and Maintenance Council (TMC) meeting a year or so ago about this problem. It may have been due to the sensitivity of ELCs to contamination by other coolants. If, for example, you take your truck for an oil change when the coolant is down 3 or 4 quarts, and as part of their service, the shop “tops off” your radiator using ordinary coolant, it alters the ELC’s long life properties. No harm may be done if a little conventional coolant is mixed in, but if the dilution reaches 2 gallons in a 12-gallon system (about 15 percent) all the long-life properties and protections are gone. Then the coolant should either be changed or treated with SCAs like any ordinary coolant. That’s why it’s important to carry your type of coolant and top-off before taking the truck for service. TMC is working with manufacturers to develop a color code identification system.
Non-aqueous propylene glycol overcomes many of the problems water-mixed coolants have. Ethylene glycol only increases antifreeze protection to 70 percent concentration. A 50/50 mix protects to minus 34 degrees F. At 70 percent, maximum protection is reached at minus 63 F. Then it falls off. One hundred percent EG will freeze at plus 4 F. Propylene glycol, on the other hand, protects to minus 27 F at 50 percent, but increase protection to about minus 76 F at 100 percent concentration. While EG is toxic, PG is so benign, it is used to sweeten children’s cough syrup.
By eliminating water, PG coolant makers such as Evans and Fleetguard offer a number of advantages. Pure PG needs no SCAs. All additives are good for the life of the coolant. PG has a higher boiling point than an EG/water mix; so it doesn’t need a pressure radiator cap the way aqueous coolants do. That, in turn, relieves stress on radiators and hoses. It also allows engines to operate hotter, which is more efficient for diesels. With no water, cavitation is eliminated at the water pump impeller and on cylinder liners. The useful life of non-aqueous PG is well beyond 500,000 miles.
With so much going for it, why hasn’t everyone switched to PG? Cost is one reason. You need twice the volume of PG than the 50/50 EG mix, and on a per-gallon basis, PG is significantly more expensive. Also, to take full advantage of PG’s benefits, you need a new radiator cap and a higher temperature thermostat. A redesigned radiator would offer even more. Not every shop carries non-aqueous propylene glycol, so maintenance on the road could be a problem if you don’t carry your own coolant.
Every cooling system should be checked periodically, but some technologies require less attention than others. The most tolerant system is the programmed SCA release, but it requires at least annual maintenance. You can order factory-filled OAT ELCs, but again, over-the-road replenishment may be almost as much of a problem as cross contamination, although more and more shops are carrying Texaco, Shell, Zerex or enginemakers’ private brands. Propylene glycol is also relatively intolerant of contamination but requires greater initial investment to get the most from it. The choice could come down to how much control you have on maintenance when away from your home base, and how much you are willing to spend.