By Christian P. Koop
Cooling system maintenance for emergency response vehicles (ERVs), in my book, has become more important than ever.
It seems to me that it often takes a back seat to other major areas such as lubrication, air filtration, and oil filtration in the overall preventive maintenance scheme. However, it is an area where failure can lead to considerable downtime and can be extremely costly to repair. I am sure most in this business will agree that this makes it even more important to ensure the cooling system is properly inspected and maintained. Additionally, the coolant itself has become more important than ever in providing the necessary protection for the highly sophisticated modern engines in use today. This article will cover a brief history, basic required cooling system maintenance and some characteristics of the diesel engine cooling system, and tips on coolant chemistry and how to ensure it is protecting the cooling system adequately.
|Using a test strip is simple and quickly reveals
glycol percentage, pH, and additive
concentrations. Be sure to follow instructions
printed on the bottle. (Photos by author.)
Cooling System History
In the early days of internal combustion liquid-cooled engines in the automotive and emerging heavy-duty truck industry, people experimented with different ingredients to keep the cooling system from boiling over in the summer and freezing in the winter. Many will be surprised to know that people added ingredients such as sugar, honey, and molasses to the water in the cooling system for this purpose. This was prior to 1927, when Prestone came out with its all-season antifreeze and coolant, which was formulated with ethylene glycol. Ethylene glycol is actually a weakly toxic, odorless, colorless, sweet, viscous fluid that, when mixed with water, will effectively lower water’s freeze point and increase the boiling point. Prestone’s all-in-one summer coolant and winter antifreeze, when mixed with the correct proportion of water, offered year-round protection. It did not need to be changed every season, making it a better choice over the ethyl-alcohol-based coolants available at the time. This was also around the introduction of the pressurized radiator cap. Prior to this, ethyl-alcohol-based coolant would slowly evaporate out of the nonpressurized systems that were the norm. This new antifreeze and coolant contained corrosion inhibitors and water pump seal lubricants.
Pressurizing the system greatly increased the boiling point of the fluid when combined with a 50:50 ratio of water to coolant. To this day, it still remains a basic guideline and an important factor. For example, a 15-pound radiator cap will provide freeze protection down to -34°F and will increase the boiling point up to +265°F. Greater concentrations of coolant to water give more protection in both directions. However, once you go beyond a 70:30 ratio of coolant to water you can actually start raising the engine’s temperature because water transfers heat better than pure coolant can. On the back of every coolant container is a chart that provides the recommended ratios of coolant to water and the freeze and boil overprotection it can provide based on the radiator pressure cap rating.
Today’s engines generate more heat than ever before, making it even more important to stay on top of the cooling system especially because there is no shutdown protection in fire apparatus if the engine overheats. If there is an overheat condition, the only thing allowed is a gradual derating of the engine-not total shutdown. This requirement is in A.18.104.22.168 in National Fire Protection Association (NFPA) 1901, Standard for Automotive Fire Apparatus. The main reason for this is to protect the firefighter at the end of the fire hose at a fire scene.
|The reverse side of most coolant containers
provides coolant-to-water mix ratios along with
freeze boil protection limits based on radiator cap
The engine control module (ECM), also known as the engine control unit (ECU) in most modern commercial trucks and over-the-road rigs, will warn the driver and shut down the engine in the event of a overheat condition. Most of these systems will give the driver enough time to pull over to the side of the road safely before complete shutdown. The main reason behind this system design is to protect the engine from serious damage along with softening the blow to your wallet. This is not so in most fire engines and rescue apparatus if they are compliant with NFPA recommendations. I have seen drivers ignore the audible and visual “overheat” and “stop engine” warnings, thinking they could make it back to the firehouse, only to cause serious and costly engine damage.
Although most literature recommends pressure testing the cooling system once a year, I think anytime the unit is in for preventive maintenance, emergency vehicle technicians (EVTs) should pressure test the cooling system, including the radiator cap. I have seen many caps that looked good but would not pass a pressure test. Passing this test is critical to keep the boiling point at optimal levels. Reducing the boiling point can stress critical areas such as the cylinder liner seals or the head gasket because vapor pockets can form and lead to damage. As many know, internal coolant leaks from the head gasket or cylinder liner seals equate to major repairs and unnecessary downtime, which can be avoided in many cases if the cooling system is properly maintained and inspected on a regular basis.
Proper Ratios Critical
If the diesel engine in your ERV is not cooled properly, the engine can reach extreme temperatures that can severely damage and destroy the engine. Only about 33 percent of the energy the internal combustion engine produces is turned into useful mechanical energy-30 percent is given up through the exhaust system, seven percent is lost through radiation, and the remaining 30 percent must be removed by the cooling system. This is why the cooling system must be properly maintained and must be able to remove the heat adequately.
Research indicates that 40 percent of all engine problems are related directly or indirectly to problems linked to improper cooling system maintenance. Modern diesel cooling systems use aluminum more and more to cut down on weight. Aluminum is very sensitive to corrosion, and if the coolant is not kept clean and does not contain the correct concentrations of additives, it can begin corroding much sooner than you would think possible.
Maintaining the correct ratio of water to coolant is very important, and ideally it should be kept at 50:50. However, extreme cold climate conditions may dictate a higher ratio of antifreeze to water. Keep in mind that a study by Cummins, Inc. has found that overconcentration of antifreeze leads to water pump seal failures. The study found that 54 percent of pump failures were directly attributed to overconcentration and that 78 percent of the pumps inspected had overconcentration regardless of the cause of failure.
The best way to test for proper ratios of antifreeze-whether ethylene glycol (toxic) or propylene glycol (extended-life, nontoxic)-is with a refractometer. The glycol is what provides freeze and boil overprotection and creates a stable environment for gaskets and seals that could otherwise shrink and leak with just water in the system. Overconcentrations of antifreeze can lead to silicate dropout, otherwise known as gelation. Antifreeze used in heavy-duty cooling systems should meet ASTM D-4985 for silicate content. If it is kept at the recommended ratio, silicate dropout should not occur.
|Shown are Detroit 60 Series liners with more than
15,000 hours and 210,000 actual road miles,
overhauled because of excessive crankcase
pressure. However, the liners have no pits, which
is indicative of correctly maintained SCA levels.
Heavy-Duty Diesel Issues
One of the inherent issues with heavy-duty diesels is that cylinder liners (wet-sleeve-type liners) vibrate because of the reciprocating movement of the pistons. As the pistons go up and down, the liner’s outer surface, which is in contact with the coolant, vibrates in and out at a high rate. This creates vacuums, and tiny vapor bubbles form. As they implode on the liner as the cycle repeats itself a thousand times per second, tiny pieces of metal are removed from the liner. This phenomenon is known as cavitation-erosion and is also referred to as liner pitting. The effects can be neutralized by using a supplemental coolant additive (SCA) that contains chemicals that coat the liner surface with a thin film to protect it from damage.
Some heavy-duty coolants may contain these additives; others will require them to be added separately. This is extremely important because if the coolant additive package does not provide adequate protection, liner pitting can be so severe that the tiny holes can eventually go all the way through the sleeve. When this happens, you are talking major dollars for an engine overhaul. The important thing to remember here is that the additives in the SCA are depleted over time and must be added to replenish and bring the system back to levels that provide adequate protection.
A cooling system issue that can impede the proper transfer of heat to the coolant is known as scaling. Minerals in water such as magnesium and calcium (hard water) are attracted to and form on hot spots found in areas such as the liners and cylinder heads. When they form in these areas, they effectively become insulators that can lead to worn rings and to oil burning when it starts getting past the worn rings, leading to eventual engine failure requiring a costly overhaul. Only 2 mm of scale can impede the transfer of heat by 40 percent, which can lead to hot spots and overheating that will eventually reduce engine life. There are additives on the market that protect against scaling by essentially wrapping themselves around these minerals, not allowing them to adhere or become attached to the hotspots. All of the major diesel engine manufacturers publish information regarding how hard they allow the water to be, the chloride levels, the sulfate levels, and the total dissolved solids that are in suspension in parts per million (ppm). They all vary slightly, and maintenance folks should be aware of them.
Rust is yet another problem that can affect cooling system effectiveness. Essentially it is caused by oxidation in the cooling system, which is accelerated by heat and moist air. Rust can flake off, causing clogs and accelerating water pump and hose corrosive wear.
Coolant aeration is caused by air leaking into the cooling system and usually manifests itself as foamy or soapy coolant. The cause can be as simple as a bad radiator cap. If not corrected in time, it can lead to pitting of various areas-particularly the water pump impellor. Technicians need to be aware of this potential problem and look for the root cause if they find coolant foaming during routine maintenance.
Another critical area to keep tabs on is the coolant’s alkalinity, or acid level. It is measured in pH and occurs over time as sulphates begin entering the cooling system. Anything lower than a pH of seven means it can cause corrosion-particularly to the aluminum parts in the cooling system-but can also attack the cylinder liners and heads. Most diesel engine manufacturers recommend a pH value between eight and 10. To neutralize these acids, borates and phosphates are used. There are various kits (coolant chemical test strips) on the market that will test for the levels of sodium nitrite, molydate, pH, and freeze point.
Electrical corrosion is caused by the coolant’s ability to carry an electrical charge and is related to the cleanliness of the coolant and the amount of dissolved solids that are in suspension. There are two types: galvanic corrosion and electrolysis. The damage they can cause to the metal parts of the cooling system is irreversible.
Galvanic corrosion is caused by dissimilar metals that are in contact with each other via an electrolyte-namely dirty coolant that has become acidic-which essentially has caused the cooling system to become a battery. Electrolysis is much faster acting than galvanic corrosion and not only can ruin radiators and heater cores but also can destroy the entire engine. It is generally caused by a high resistance or missing ground of an electrical device, which uses the coolant as the path of least resistance. As current draw goes up in this circuit, the destruction level and rate go up. To test for these two phenomena, technicians need to use a digital voltmeter, placing the negative lead on the engine ground and the positive in the coolant at the radiator neck. Readings greater than 400 mV (0.400) indicate that the coolant has become acidic, which happens with age and essentially has caused the cooling system to become a wet cell battery. This condition will require EVTs to flush and clean the system. Then they should run the same test with the key in the engine-off position (ensure battery switch is on if so equipped) but place the negative lead on the chassis ground, engine ground, and battery ground. Any voltage readings greater than 400 mV indicate a high resistance ground that needs to be corrected.
The role of coolant has evolved very much in recent years, and manufacturers have improved its ability to protect the engine. There are various types of coolant available on the market, and manufacturers have different color codes to help users differentiate between them. The colors also help technicians locate hard-to-find leaks. Some coolants are designed to last two or three years and up to 36,000 miles, while others are designed as long-life or extended-life coolants and may last five years, 600,000 miles, or more. There are also several on the market that are designed to last eight years, 1,000,000 miles, and more than 8,000 hours. They have different chemical packages, and some require adding SCA somewhere along the line while others don’t.
Maintenance personnel should become familiar with these and use what best suits their fleets based on operation, climate, service levels, types of units in the fleet, engine manufacturers, and the expected service life of the equipment. Following are some of the types of antifreeze and coolants on the market today, along with some common chemicals used in antifreeze and in additives along with their purpose. These are only brief descriptions, and I recommend that those not familiar do more research to gain a better understanding of the different antifreezes and coolants and what the chemicals they contain do. Keep in mind that inhibited ethylene glycol and propylene glycol is still the major component of antifreeze and coolant.
- Inorganic acid technology (IAT): The original green coolant designed for cars and light-duty trucks.
- Hybrid organic acid technology (HOAT): Low-silicate nitrate technology, commonly dyed yellow or orange and generally requiring SCA to be added at specific service intervals. It should not be mixed with extended-life coolants like NOAT or OAT.
- Nitride organic acid technology (NOAT): Extended-life coolant designed to last 300,000 miles or 6,000 engine hours before adding a supplement that can double its expected life.
- Organic acid technology (OAT): Coolant with no nitrite added and designed to last 600,000 miles or 12,000 hours. But, service life will be reduced if contaminated with coolant containing nitrites.
- Borates and phosphates: Maintain proper pH levels and provide corrosion protection.
- Silicones and polyglycols: Prevent foaming and water pump cavitation.
- Nitrates, silicates, tolyltriazole, and organic acids: Corrosion protection for various metals.
- Nitrites, molybdates, and organic acids: Cast iron cavitation corrosion protection.
- Polyacrylates and other water soluble polymers: Keep mineral deposits from forming on hot spots.
The role of the cooling system is vital to the proper operation and life of the engine. Don’t wait to check this system on an annual basis. Any time ERVs are in your shop for routine preventive maintenance it will pay off to perform a pressure test of the cooling system, including the radiator cap, and to check the chemical health of the coolant with a test strip. Performing this simple procedure can go a long way toward preventing unnecessary and costly ERV downtime.
CHRISTIAN P. KOOP is the fleet manager for the Miami-Dade (FL) Fire Department. He has been involved in the repair and maintenance of autos, heavy equipment, and emergency response vehicles for the past 35 years. He has an associate degree from Central Texas College and a bachelor’s degree in public administration from Barry University and has taken course work in basic and digital electronics. He is an ASE-certified master auto/heavy truck technician and master EVT apparatus and ambulance technician. He is a member of the board of directors of EVTCC and FAEVT and a technical com mittee member for NFPA 1071, Standard for Emergency Vehicle Technician Professional Qualifications.