Coolant used for heavy duty DIesel engines has changed considerably in recent years. Most heavy trucks now use Extended Life Coolant, or ELC to protect engines from freezing in cold weather, boilover in hot weather, and corrosion and cavitation at all times. The coolant needs to be tested periodically to make sure the proper protection levels are maintained. conventional anti-freeze is composed of ethylene glycol, with a silicate-borate corrosion inhibitor. ELC is composed of ethelene glycol with a nitrate based corrosion inhibitor.


 Anti-freeze formulation has changed both in the color and composition over the years.  the biggest changes began after the oil embargo of the '70's when car makers started making smaller, lighter cars that used more aluminum componants such as engine cylinder heads. These engines required anti-freeze with high levels of silcates to prevent damage to the aluminum parts. This formula created a problem for Diesel engines, the high silicate formula would form a slimy "Green Goo" that would drop out of the solution and plug oil coolers, heater cores and radiators when used in Diesel engines without the need for the high silicate formula. This problem created a need for a "Low Silicate" coolant formulation for trucks and equipment with Diesel engines.


  As coolant technology has advanced over time many other special needs were identified. This resulted in several specialty formulations, and different colors to identify each one, Red, Gold, Blue, Fuscia, Green, and sometimes orange and yellow. Sorta like all the flavors you get with a sno cone! It is important to use compatible formulas when adding to your system to prevent problems. There are two different coolants that are primarily used for heavy duty trucks, conventional low silicate formula colored green which most often uses a water filter with a chemical to recharge the coolant as it gets depleted, and a long life nitrate based coolant that can go much longer before needing replacement, which is colored red. Long life systems normally do not use a water filter. For this discussion I will cover testing these two which are the most common in trucks.


 Over time the chemicals in the coolant become depleted and no longer protect the metals and other parts in the cooling system. also the freeze and boilover protection can change from adding coolant when needed. Testing shows the level of protection and when a supplemental additive is needed to bring the protection level back to the optimum level. This is a fairly simple test using a test strip. While the procedure for both coolants is similar, the test strips are different because of the chemicals used for each formulation. Make sure you get the proper test strip for the coolant you have. For ELC there are normally 3 pads on the strip showing PH level, freeze protection and nitrite level. Test strips have a shelf life, make sure the expiration date on your test strip is ok or the test results may be inaccurate. Test strips can be found at fleet suppliers, dealers, and engine shops.


The best way to do the test is to drain a sample into a clear glass container. make sure the engine is cooled down before you drain a sample to prevent injury. Verify the color of the coolant, if it has been diluted or mixed with different colors the test may not be accurate. Dip the strip in the coolant for several seconds, remove and shake off excess coolant. Following the directions compare the pads on the strip with the color chart on the bottle or package. If the level is low add the recommended extender for the coolant you have. For ELC this is normally needed at 300,000 mile intervals, with an overall life of 5-6 years. For conventional green coolant without a filter a supplemental addditive is normally needed about once a year, or 100,000 miles with a life of 2 years, or when the total dissolved solids in the solution reaches the maximum level. If a filter is used it should be changed once a year and should not require additional treatment. you can verify the protection level at the next service if needed.


Do not exceed the recommended level of chemical in the coolant. The conventional wisdom " if a little does a little good then alot will do alot of good" does not work with coolant additives. if the chemicals become overconcentrated the result can be worse than not having enough. Deterioration of hoses, liner orings, water pump seals, etc. can result from too much additive. Remember the purpose of the test is to keep the concentration at the proper level. Over servicing of the coolant filter can cause overconcentration of additives as well. Test your coolant regularly and add extender based on the results of the test. Detailed coolant testing can also be done at most labs that do oil analysis. This can be helpful if you need to identify something in the coolant, but is not normally needed and costs more than using a test strip.


When you need to add coolant, be sure you have the proper type, use prediluted coolant unless you need to make the solution stronger. If you need to add water make sure you use de-ionized or distilled water. Hard water that contains minerals will leave deposits in the cooling system. Some coolant colors and types are universal which means the additives are supposed to be compatible with all coolant types. In reality these are compatible to a certain concentration level, say 20%, and they may make the original corrosion inhibitors less effective, plus give a false reading when tested. I would strongly recommend you use the same coolant when adding. If you have green coolant the best thing would be to drain and flush the system and refill with ELC. If your coolant is diluted with different colors drain, flush and refill with ELC. The coolant is a life blood for your engine.  Do not add universal, or different color coolants unless it is an absolute emergency. You wouldn't want to mix different blood types in your body would you? It's not a good idea in your cooling system either.


Taking the time to test and maintain your cooling system can prevent may problems and costly downtime. Make sure you know what coolant is in your truck and test it regularly to keep your truck happy.