Lessons Learned – by Pat Carson
Engine Antifreeze AKA Coolant
That bright colored product in your vessel’s engines is a hardworking liquid, and unfortunately it is often ignored. To keep your engine operating at a proper and efficient temperature, coolant circulates through the engine and into the heat exchanger where raw water removes the heat and sends it out the exhaust. An operating engine typically converts only one third of the energy derived through the combustion of fuel to propel the vessel. The other two thirds are converted into heat, one third of which goes out with the exhaust. This leaves the remaining one third of the heat in the engine block, thus we use coolant to adsorb it. But coolant does more than just control engine operating temperature; its additives also prevent scaling that interferes with heat transfer, corrosion that damages internal metal components and cavitation that damages cylinder liners in diesel engines. The fluid testing lab that we use reports that cooling system issues account for nearly 40% of all engine related problems. Interested in reducing engine related problems, keep reading.
Ethylene Or Propylene Glycol Plus Deionized Water Plus Corrosion Inhibitors = Engine Coolant
The unique differences between coolants are primarily dictated by the type of glycol used (either ethylene or propylene), the water (deionized or distilled) and the corrosion inhibitors used. Each corrosion inhibiting technology system is designed for specific or broad application, depending on the coolant application and environment in which it is to function. Coolants consist of a base, Ethelene Glycol or Propylene Glycol mixed with water, deionized or distilled, manufacturer specific additives and corrosion inhibitors. Ethylene glycol-based coolants are less expensive and have better heat transfer performance, but are toxic. Propylene glycol is non-toxic and more expensive, but is the glycol of choice where a low toxicity product is required. These coolants would typically be labeled as non-toxic antifreeze.
Coolant falls into three basic groups: Inorganic Acid Technology (IAT), Organic Acid Technology (OAT) and Hybrid Organic Acid Technology (HOAT).
IAT uses an Ethylene Glycol base, along with additives that rely exclusively on inorganic salts such as nitrates, phosphates and silicates for engine protection. However, formulating exclusively with inorganic salts has drawbacks. These additives deplete quickly and will cause the buildup of sludge and scale if proper maintenance is neglected. Most of us remember the good old “green stuff” that we used in cars and boats forever, and this is the low cost IAT coolant. Green coolant has a service life of two years and must be changed for continued engine protection.
OAT uses a Propylene Glycol base and does not contain phosphates, silicates or other inorganic salts, and therefore eliminates the problems associated with the “green stuff.” Plus, the service life of OAT coolants is five years in normal service.
HOAT coolant uses a Propylene Glycol base and relies heavily on organic acids but strategically uses inorganic salts to make use of their protective properties. HOAT coolants deliver the long service life of five years and have excellent engine protection.
A Rainbow Of Pretty Colors
All coolant starts out clear and the manufacturer adds dye to change the fluid to a color. In addition to the “green stuff,” we have a rainbow of colors including orange, yellow, amber, red, pink and blue. However, if you mix the wrong ones together you get a not so pretty brown. The different colors generally identify the type of coolant being used. IAT coolant is green, OAT coolants are red, pink or blue and HOAT coolants are orange or yellow but can also be red or green.
The more common engine coolant uses a 50/50 mix of ethylene glycol and deionized water plus small amounts of other ingredients including corrosion inhibitors, antifoams and of course, the green dye. While these other ingredients make up only a small percentage of the overall coolant formulation, they are what differentiates one coolant from the other. Green coolant or IAT, uses a phosphate and silicate mix as the main component in their corrosion inhibitors. These inorganic chemicals work by forming a protective blanket that insulates the metals from the coolant and is then depleted during this process. For this reason, green coolant requires changing at regular intervals, usually every two years.
To replace the environmentally unfriendly phosphates, the European coolants contain a mix of inorganic silicates and organic carboxylates for corrosion protection. Rather than forming a layer of inhibitors like the phosphates, the carboxylates provide corrosion protection by chemically interacting at the corrosion sites. The mix of carboxylates and silicates is referred to as a hybrid technology or HOAT because it is a mix of conventional inorganic technology and not fully carboxylate or organic technology. European engine coolants exist in various colors, typically orange and yellow.
In Asia, problems with water pump seals and poor heat transfer led to the ban of coolants containing silicate. To provide protection, most Asian coolants contain a mix of carboxylates and inorganic inhibitors like phosphates. These coolants are considered hybrids, but they are distinctly different from the European hybrids due to their lack of silicates. These silicate free coolants are a variety of colors including red, orange and sometimes green.
Extended life globally acceptable organic coolants, OAT, are carboxylate-based coolants that have no silicates, meet the Asian requirements, have no phosphates and therefore meet the European requirements. These coolants are usually red, pink, or blue.
Marine engine manufacturers’ recommendations have a wide array of differences. Some require the use of a coolant with silicates while others require silicate free for heat transfer concerns. Some require phosphate-free coolants to avoid hard water scale deposits that form on the hottest part of the engine which reduces heat transfer and can potentially induce corrosion. Some manufacturers require the use of nitrites to protect against cavitation while others have no such requirement. Given the phenomenon of cylinder liners, cavitation is design specific, so not all engines react the same way.
If you are still reading at this point, you have realized that not just any coolant is right for your expensive marine engine. It should also be apparent that mixing different coolant chemistries or color for simplification, is not a good idea. In fact, mixing of some coolants will produce a gel like substance and plug up the heat exchangers, reducing heat transfer and engine performance. The color of the coolant in your engine may be a first indicator that you have something other than the traditional green, however never rely on the color to determine exactly what type of coolant you have. There are no industry standards for manufacturers as to what color to use for specific coolant formulations.
The Cap Is Important As Well
The coolant is just one part of the total cooling system. We can raise the boiling point of the coolant by using a high-pressure cap. You probably know this as the radiator cap in your car. For every one pound per square inch (PSI) we increase the system pressure, the boiling point of the coolant is increased by three degrees Fahrenheit. A pressure cap in a modern marine heat exchanger is 15 PSI, which raises the coolant boiling point by 45 degrees. Older marine engines use pressure caps from one to seven PSI. Newer heat exchangers are made from aluminum instead of the older brass and copper ones, and since aluminum has a higher tensile strength than brass they are able to operate at higher pressures. Not only is aluminum able to operate at higher pressures, it is lighter and thinner resulting in larger diameter internal tubes for improved heat transfer.
As the coolant heats up, it begins to expand and creates additional pressure. By allowing that pressure to increase, the boiling point of the coolant is increased to around 257° F (125° C) with a 15-PSI cap. This gives us better performance from our cooling system as it absorbs additional heat from the engine without boiling. What happens when the pressure exceeds the system’s PSI rating? As you may have guessed at this point, regulating the pressure within the cooling system is the job of the pressure cap. The valve opens up and allows excess coolant to flow into the coolant overflow. As the engine cools down and the pressure in the system drops, the pressure cap allows the excess coolant in the overflow tank to then return to the system by use of a second spring loaded valve. This second valve responds to the vacuum created in the system from the drop in pressure and pulls the coolant out of the overflow tank. Not only does this recycle the excess coolant to prevent air pockets in the heat exchanger, but it also prevents the softer components of the cooling system such as the hoses from being crushed by the external air pressure.
Be careful as pressure caps not only have different pressure ratings, but they also come fitted with one or two-way valves. In the old days, the pressure cap was a one-way valve that allowed coolant to flow into the bilge when the pressure increased above the limit. But since recovery tanks were not fitted back then, the pressure caps lacked the secondary valve to let coolant flow back into the heat exchanger as the system cooled. If you put a one-way cap on an engine designed to allow coolant to flow back and forth between the overflow tank, the heat exchanger will be continually low on coolant and may not perform as designed.
Testing, Testing, Testing
Anything other than good looking, clean smelling and slippery coolant is an indication that it is time for change. Just like we would check our engine’s lubricating oil by rubbing a small amount between the fingers to see if it is slippery and has no grit, smell it to see if it has a burnt odor and look at the color, we do the same for coolant. A small amount between your fingers should be slippery and not gritty, it should not smell burnt and visually it should look clean with a vibrant color. As part of a good maintenance program, we do annual coolant chemical analyses at the same time we send oil samples to the lab for analysis.
The lab that we use for oil and coolant sample analysis reports that over 40% of engine failures are due to problems with the cooling system, confirming that this vital system is one of the most neglected and least understood systems of the engine. Regular coolant testing and routine maintenance can achieve maximum system performance and identify potential problems before they become catastrophic failures.
There is more to coolant analysis than simply testing the coolant formulation. Analysis can identify problems within the cooling system that can be detrimental to engine performance or lead to premature engine failure. Coolant analysis can detect metal corrosion, combustion gas leaks, contamination, electrical ground problems, overheating and chemical breakdown.
By performing regular coolant analysis, the drain intervals of extended life coolant can be extended up to eight years and we can identify minor problems before they become major failures. Extend the life of the engines, lower maintenance costs and improve reliability with basic coolant analysis.
The following tests monitor coolant maintenance levels to ensure proper engine metal protection, glycol levels for freeze and boil point control, nitrited coolant for prime metal pitting protection, acidity/alkalinity of the fluid and visual contaminants.
Coolant chemical analysis should be part of every vessel owner maintenance program, especially if you are not using the coolant recommended by your engine manufacturer and have not changed the coolant at the recommended intervals.
Bottom line on coolant, if you have a Volvo engine use Volvo coolant, a Caterpillar engine use Caterpillar coolant, a Cummins engine use Cummins coolant and an engine that you do not care if it lives or dies, use whatever is on sale. Do not forget that the proper ratio is 40 to 50% coolant and 50 to 60% distilled or deionized water. How many times have you seen or heard of someone just pouring water from the tap into the heat exchanger? Even filtered water has contaminants that negatively affect the cooling system, and who knows what is coming from that marina hose. If you have no time to mix the proper ratio with the proper water, then instead of using the concentrate buy the premixed coolant that has the proper ratio of water. Keep a gallon or two of premixed coolant on board for system top ups between servicings and to help you remember what coolant you are using in the engines.
There is not a week that goes by that I do not see a cooling system issue. Mostly plain old green coolant that is closer to brown, a generic brand product of unknown chemistry used in a $100,000 diesel engine or an engine overheating that is not corrected by changing the raw water impeller due to scale and sludge in the cooling system. These conditions are all preventable by using the correct coolant as specified by the engine manufacturer and changing per the recommended interval, two years for the green stuff and five to eight years for the modern extended life stuff.
The aftermarket is filled with high and low-quality coolants of all colors; therefore, color is not a perfect indicator of the type of coolant. There are even some coolants that state that they are compatible with any other coolant – be very careful of those. The best maintenance practice is to know the exact coolant the manufacturer specified, use that and change it at the specified intervals.
I have seen some owners that change their own fluids by placing a drain pan somewhere under the heat exchanger and loosening a hose. While this is better than not doing anything, you might get at best half of the coolant to drain into the pan this way. Which means you are leaving 50% of the dirty worn-out old coolant inside the engine. Check the engine manufacturer’s recommended coolant drain procedure and follow it. If the engine manufacturer states that the cooling system holds 10 gallons of fluid, then you should have two full five-gallon buckets after you properly drain the system.
The cooling system is critical for engine performance and long trouble-free service. If you have not serviced the cooling system, now is a good time.
Time for me to sit back, enjoy a good glass of port and light up a fine cigar while I wait for my annual coolant and lubricating oil analysis reports so that I can see how the internals of those expensive power plants are doing. Until next month, please keep those letters coming.
The next Lessons Learned will be “Is it right or is it wrong.” If you have a photo or two, please share. If you have a good story to tell, send me an email at firstname.lastname@example.org as I love a good story.