Truck Checks: Coolant problems in fire apparatus
By Don Henry
Coolant problems in fire apparatus
By Don Henry
It's green and good for -40 C, so what more do I need to know about engine coolant? A lot more, actually. The colour and the antifreeze concentrate level are only two of many factors that need to be considered. First, let's look at the job of the coolant in an engine and then the differences that affect fire apparatus use.
A common guideline for the internal combustion diesel engine is that one third of its power comes out of the driveshaft as usable power, one third comes out as heat from the exhaust system, and one third comes out as heat from the radiator. This heat transfer is possible because of the coolant carrying that very destructive heat away from critical engine parts and into the cores of the radiator. This heat is transferred through the copper or aluminum cores of the radiator. The vast majority of cooling system failures are caused by neglect, pure and simple. In 2002, the cooled exhaust gas engine began to appear. These engines put an even larger heat load on the cooling system and require more attention to cooling system maintenance.
The major parts of a heavy-duty diesel engine coolant system are the radiator, radiator cap, water pump, thermostat, coolant filter, water jacket and, of course, the coolant itself. The radiator with its many minute passages allows the coolant to slow down. This, in turn, allows the coolant time to transfer its heat to the air moving through the radiator fins. The radiator pressure cap is very often in the range of 10 psi (70 Kpa) to 17 psi (100 Kpa). Raising the coolant's pressure will increase the boiling point of the coolant about three degrees F for each psi.
The engine's water pump can pump 30 to 50 gallons per minute. The coolant system normally holds about 20 gallons. This means the coolant is cycled through the engine to the radiator two to three times per minute. By the way, it has been estimated that an engine can produce enough heat to completely melt that same engine into a puddle of metal in about 10 minutes.
The coolant filter removes scale and rust. The coolant filter may also be able to add additives to the coolant system to control corrosion. Not all engines have a coolant filter, but they do extend the service life of the coolant by many times.
The thermostat's job is to ensure the engine is at or near operating temperature (some engines have two thermostats). If the engine is run cold, then the engine's oil will be contaminated with water and sulphur, byproducts of incomplete combustion. If the thermostat is defective and does not open or the coolant level is low, then the engine can quickly overheat and serious damage can result quickly. Most modern diesel engines operate between 100 C (212 F) and 115 C (239 F). You are not being kind to the engine to put in a lower opening temperature thermostat than that recommended by the engine manufacturer.
Coolant levels: In the past it was necessary to remove the radiator cap from the tank (only when it is cool) and look in to ascertain the level. You wanted to make sure the coolant was above the level of the radiator cores but a few inches below the neck of the radiator. If the radiator was too full, then as the coolant heated and expanded, it would be forced out of the radiator. Unfortunately, each time the cap was removed to check the level, oxygen in the air would come in contact with the coolant and the coolant service life was shortened. Modern apparatus have expansion tanks on the side of the radiator. This helps to keep the corrosive effects of oxygen from the coolant.
If the coolant is rusty or milky in colour, the coolant system needs immediate servicing. Most modern electronic diesel engines have coolant level sensors. These sensors detect when the coolant level is low in the radiator. The level sensors and the coolant temperature sensor can be a concern for the pump operator. An electronic engine has the ability to de-rate its performance and even shut itself down if it detects a problem in the cooling system. It is possible to disable this feature on fire apparatus. In fact, NFPA 1901 requires it to be done.
There are other components such as the cab heater, engine, transmission oil coolers, fire pump transfer case oil cooler and, of course, the auxiliary radiator cooler normally found only in fire apparatus.
Antifreeze types: Ethylene glycol solution became available in the late 1930s and was our first permanent antifreeze. Propylene glycol became available in the late 1970s; it cost more money but was less harmful to the environment. Both are in use today. The next generation of coolants are called organic acid antifreezes. They are normally ethylene-based but contain corrosion inhibitors made of organic salts. They do not contain phosphates or silicates, two compounds that caused problems with early antifreezes because of dropout. These organics can be divided into three groups: OAT (organic acid technology), HOAT (hybrid organic technology) and NOAT (nitrate organic acid technology).
Each coolant has its advantages. It can get a bit confusing, but I have information that is available for free at the end of this article that helps to sort them out. Coolant colours are now green, red, blue, pink or yellow. At the present time, there is no ASTM (American Society for Testing and Materials) standard regarding the colours of the different coolants. Manufacturers will have their own.
The coolants are a mixture of antifreeze and water, but not just any water. The water should be at least deionized or better yet, distilled. In many cities the tap water is simply not good enough to put into an engine. For those of you who have trained at the Alberta Fire School in Vermilion, you will know what I mean. This is the reason that many manufacturers sell their product pre-mixed. This pre-mix is usually a 50-50 mixture of antifreeze and water.
I know that you are probably thinking, "Do I look stupid enough to buy water when I can get it almost for free from a tap?" If you want long service life, you will need to use good water. The best antifreeze is long life (also called extended life) antifreeze and this antifreeze almost always comes pre-mixed. This allows the manufacturer to maintain control of the water quality. This coolant can get you 10 or more years of service use with extended life antifreeze if its condition is properly monitored. I have often seen home-mixed antifreezes that did not last two years.
Water by itself is not considered suitable for high performance diesel engines. It's not just that water freezes at 0 C and boils at 100 C, but plain water does not contain any antifreeze additives. These are essential to stop the engine cylinder liner pitting, also known as cavitation. An early sign of liner pitting is a milky white substance floating on the top of the coolant in the radiator or on the bottom of the radiator cap. This is engine oil. If you can detect this problem in the early stages, then you will need to have only the engine rebuilt. If the problem is not fixed, then a complete engine failure will result in the very near future.
Many pump operators know how to recognize the sounds of cavitations in the fire pump and understand the destructive results of cavitations. These sounds are almost impossible to hear in a running diesel engine, but let me assure you they are just as destructive and can happen very quickly. The cylinder liners will develop cavitation holes (see Fig. 4). The result will be antifreeze in the motor oil, and the engine will be destroyed shortly. Even if the antifreeze protection temperature level is good for -40 C, the corrosion package can be depleted. Normal antifreeze may last only two or three years; long life antifreeze (with additives) can last in excess of 10 years.
These pour-in additives are called supplemental coolant additives (SCA) (Caterpillar calls its product Cat Extender). These SCAs can also be incorporated as part of the coolant spin on filter. It should be stressed that you should not use a SCA on Caterpillar extended life coolant and vice versa. These SCAs protect the engine against cavitation, corrosion, rust and scale but like most things in life too much of anything is not good for you. It is possible to add too much SCA to an engine. Too much SCA will cause additive fallout, plugging of radiator cores, and overheating and hot spots. You will need to get your antifreeze tested by a competent technician to know just how much and how often these SCAs will need to be added. This can normally be done in the shop while you wait or even in your fire hall with the use of test strips.
You could simply drain, flush and replace your complete coolant system every two years, but that would be expensive and remember that the old coolant must be properly disposed of. I don't recommend the purchasing of used (recycled) coolant from the back of someone's truck. The formulas are just too complicated to get it right. If you are forced by your city to consider such purchases, subject the antifreeze to a complete fluid analysis by the same people who conduct your engine oil analysis. If the seller of this recycled antifreeze will not pay for the test, then walk away from the deal.
As I have said on many occasions, fire apparatus have unique maintenance concerns. Here are just three examples. Most trucks get the benefit of road draft (the movement of air through the radiator and around the engine at road speed). Fire apparatus, when pumping at a fire, do not have the benefit of this cooling air flow. NFPA 1901 requires the apparatus to have an auxiliary cooler installed to combat this problem. This cooler is controlled from the pump operator's panel; therefore, you can see the need for an operating engine coolant temperature gauge on the pump panel. If the operator were to see that the temperature was climbing, then the valve on the pump panel could be opened and a very small amount of cold water from the fire pump could be sent to the auxiliary cooler. These coolers are very effective. You do not need to worry about cracking the engine block; the cooler is downstream from the engine but before the radiator top tank.
The only way to effectively conduct an operational test on the engine coolant system is to find a suitable water supply and conduct the complete NFPA pump test; this will take over three hours. The reason for this test is that an engine that remains cool driving down a road at 100 km/h will overheat when pumping water. I have found cases on dual thermostat engines where one thermostat was defective but was not detected until the fire pump was put to a proper pump test. (Yes, you will burn up some diesel fuel but it is the only way to detect a problem in the coolant system.) A simple 10-minute pump test will not reveal these problems. Remember, you cannot remove any panels or open any hoods during the pump test to keep the engine from overheating.
Make sure to use an extended life antifreeze that meets ASTM D6210 (see below). Most engine manufacturers have extended life antifreeze products; use them and stick with them.
If you use an extended life antifreeze, top up the radiator with only the same type of antifreeze, or you will lose the advantages of this antifreeze. Occasionally, two different antifreeze types can cause engine cooling failure and possibly engine damage.
Engine coolant used to be very simple. It has become much more complicated in the last few years with the advent of the many different types of antifreeze now available. Heat loads that the coolant system are now expected to remove from the engine are greater and the need for coolant maintenance even more critical. An excellent, free interactive training CD is available from Baldwin Filter (number PKG475). It covers oil, coolant and fuel systems and their maintenance. Contact Jean Seitz, e-mail firstname.lastname@example.org and tell them that you read my article on coolants and want a copy of the CD.
Sorting out coolants
ASTM D6210 is the most important heavy-duty publication. It specifies the physical and performance requirements for virgin and recycled ethylene and propylene glycol antifreeze and pre-diluted coolants intended for heavy duty applications. This is the specification currently required by most diesel engine manufacturers.
ASTM D6471 specifies the physical and performance requirements for recycled ethylene glycol pre-diluted coolants intended for light duty applications.
ASTM D6472 specifies the physical and performance requirements for recycled ethylene glycol concentrates
ASTM D4985 is an obsolete specification. It specifies the physical and performance requirements for virgin ethylene glycol intended for heavy duty applications that require a pre-charge of supplemental coolant additive. Coolant that meets only this specification is no longer acceptable to most diesel engine manufacturers.