The main function of a coolant is to facilitate heat transfer in an engine. In addition, coolant must also resist the harmful effects of acidity, prevent corrosion and scale, minimize liner pitting, and reduce the likelihood of precipitates / additive drop-out which could plug up the system.
Coolants & SCAs
Conventional coolants were designed to start with a very alkaline formulation and include corrosion inhibitors, such as phosphate, borate, silicate, nitrite and nitrate, which would get used up quickly. As such, the pH would drop as the coolant was left in service. Field mechanics were generally trained to use test strips to monitor the pH at every service, so they would know whether to top-up the system with SCA (Supplemental Coolant Additive). As field mechanics often were required to perform the testing in the field, and to respond correctly, it was difficult to achieve consistent pH on a universal basis across all engines in the fleet. Coolant pH levels could vary widely with some engines having levels that were too low while others had high pH levels due to over-dosing the system with SCA.
Auto-Leeching Coolant Filters
To resolve some of these issues, coolant, filter, and engine manufacturers developed auto-leaching coolant filters that would slow-release the SCA on a more consistent basis. While this was an improvement, it still didn’t fully solve the fundamental issue with maintaining a stable coolant formulation over time. PM service intervals were very short, and coolant leaks were very common due to the hardening of elastomer materials used in the engine. At the same time, the wide variations of pH levels would result in excessive corrosion of different metallic surfaces (i.e. iron prefers lower pH, aluminum prefers higher pH, etc.).
Extended Life Coolants
ELC’s were designed to solve many of the problems associated with conventional coolants. ELC’s use a different chemistry (generally organic acids) which has a more stable pH level, and thus more predictable levels of corrosion and longer coolant life. The requirement to monitor ELC’s using test strips was eliminated, and the service intervals were extended quite dramatically, provided the coolant levels were maintained consistently. The thinking here was that if the coolant levels got too low, then the coolant would be thermally stressed and degrade prematurely.
Effects of SCAs on Extended Life Coolant
What happens if you top off an Extended Life coolant with SCA or use auto-leaching SCA filters on your system?
Over time, you should expect the pH to gradually increase, while at the same time, the additives would build up. You may see this in terms of an increasing conductivity, or worse, a higher risk of additive drop-out. The type of additive drop-out that you may experience depends on the exact nature of additives being used in the SCA releasing filters. Phosphorus based additives tend to drop-out as a gel, while silicate-based additives tend to drop-out as a hard white scale. Gelling is a problem because it impedes coolant flow, while scale is a problem because it greatly restricts heat transfer capabilities. You may also notice this in terms of higher engine temperatures, or a less efficient cooling system. Either way, this would be a good thing to explore through routine coolant testing.
Coolant Testing
Most of engine OEM’s specify that ELC’s should not be mixed with conventional coolants. If a mixture of coolants is detected, OEM’s recommend that the PM service intervals should be shortened and changed at the next interval.
If you are in a situation where SCAs and ELC have mixed, we recommend starting off with assessing the baseline coolant, and then doing a coolant sample across the board on all units for a given fleet. You can then do ‘bad actor’ analysis to determine which units are most at risk of cooling system issues and perform a more thorough inspection as needed. You can then evaluate your protocol of using SCA filters with ELC coolants and make a change to your standard operating procedures if necessary. Finally, if you find value after going through this process, consider adopting routine coolant testing as a standard part of your maintenance program.
Talk to us today about developing a coolant testing program.