ENGINEERING SOLUTIONS / Post date: 1 July 2016
In this issue, we are continuing the discussion on Cooling System Maintenance that we began in the last edition of HD Focus. Just to recap, we reviewed the danger of cross-contamination of cooling systems with coolants of different technologies and recommended consolidating to just one type of coolant for your fleet. The dangers of scale build-up from using hard water and the need to use softened or deionized water were also reviewed. As a reference, the first article can be found at: http://castrolhdfocus.com/cooling-system-maintenance-part-1/
So, let’s move on to review periodic maintenance. There are two main areas of concern with cooling system maintenance…the cooling system components and the coolant. Both require attention during system maintenance. Let’s begin with the maintenance of system components.
A typical cooling system consists of the internal coolant passages within the engine and external components, such as the water pump, radiator, overflow tank, hoses and tubing, and the fan and fan belts. The most basic system maintenance is simply checking the system for the correct level of coolant and, if required, topping the system off to bring it up to the correct level. This should be part of a daily pre-trip inspection for commercial vehicles.
Of course, if the system is losing coolant on a regular basis, then the next step would be to identify the source and repair the leak. To follow up on this condition, techs should visually observe the condition of all hoses and tubing and check the tightness of hose clamps. Hoses that are showing age should be scheduled for replacement before they fail and cause loss of coolant and an overheating condition. Look for a softening of the outer layer of a hose that gives it a spongy feel, as well as splitting or cracking,
After that, the next basic step of system maintenance is to make sure the radiator is free of debris that can clog it and obstruct air flow past the core. The radiator functions by transferring heat from the coolant through the walls of the core to the air flowing over and past the core. If the core is obstructed, then the transfer of heat may be impeded and overheating can result.
The type of debris on or in a radiator depends on the operating conditions of the specific machine involved. Soil, sand or larger items like paper and leaves can be culprits. No matter what the debris is, it must be cleaned out. Care must be taken to not damage the radiator when cleaning it. Hitting the radiator with a blast of pressurized water can bend the cooling fins and may cause an additional obstruction to the air flow.
The scheduling of radiator cleaning should depend on operating conditions. Some pieces of equipment, working in extremely dusty conditions, require that the radiators are blown out twice a day, every day. That may be extreme, but is an example of how maintenance scheduling needs to adapt to the needs of the equipment, not the other way around.
And finally, the condition of the fan belts, sheaves and tensioners should be checked. If any of these components is worn or out of adjustment, belt slippage can occur, which can result in additional wear of both the belt and the sheaves. This can lead to reduced air flow and overheating.
Now that the mechanical bits have been addressed, focus should be on maintaining the coolant itself. Periodic coolant maintenance should include testing that can be performed on-site, as well as off-site lab analysis. On-site testing should include a visual check of the coolant for color and clarity, as well as the possible presence of contaminants. The coolant’s freeze point, pH level, and nitrite and other additive levels (for SCA or NOAT type coolants) should also be tested.
These tests are performed by first collecting a sample in a clean, clear sample jar that allows a visual inspection for color, clarity and visible presence of contaminants. The color should be compared to a sample of fresh coolant. If the color is substantially less intense than the fresh coolant, it could indicate the coolant has been diluted with water. If the coolant is a different color, it could indicate the coolant has been contaminated with one of the following: 1) A different brand and/or type of coolant, 2) Engine or transmission oil, or 3) Rust and corrosion.
Engine or transmission oil contamination indicates a possible oil cooler failure, or depending on the make/model of the vehicle, it could indicate a failure of other system components such as the head gasket or cylinder liner seals. These type of failures need to be diagnosed and repaired first, followed by a thorough flush and refill with fresh coolant. Rust indicates a system that has been allowed to run low on coolant level or has low coolant strength. Rust contamination may require a chemical cleaner to be used in the system, followed by a thorough flush and refill with fresh coolant.
Once a visual inspection of the coolant has been made, a coolant test strip and hydrometer or refractometer should be used next.
Depending on the type of coolant used in your fleet, there are numerous test strips available. For SCA-type coolants, you should use a test strip that measures the strength of the supplemental coolant additives, such as Nitrites & Molybdates, as well as the freeze point and the pH of the coolant. For OAT-type coolants, you should use a test strip that measures the freeze point and the pH of the coolant. Test strips are a fast and easy way to check on the condition of a coolant, but should not be the only means of testing.
In addition to the test strips, it is recommended that the freeze point is checked by using a hydrometer, or better yet, a refractometer. Both of these tools are easy to use and the testing can be quickly performed. A hydrometer is a simple device that measures the specific gravity of a liquid. To use a hydrometer you simply draw a sample of the coolant up into the meter and read the results on a float that will tell you the freeze point in degrees Celsius or Fahrenheit. A refractometer is more accurate. It is a device that uses the refractive properties of elements to identify the concentration of glycol in water and it reports the freeze point in degrees Celsius or Fahrenheit. Both of these tools are relatively inexpensive and are well worth the investment. They can also be used to monitor the condition of lead/acid batteries as well, making them even more useful in your shop.
Using one of these tools along with test strips will help you to understand the condition of the coolant. If the test strips indicate a low level of coolant additives or a low freeze point, then topping off with fresh coolant can help to correct that condition. Sometimes you may need to drain part of the existing coolant from the radiator to make room for more fresh coolant. You should repeat the process of testing after the fresh coolant is added, and based on the results of the re-test, you may need to continue to add additional fresh coolant and re-test until you get a satisfactory reading.
It is recommended that a coolant field test is performed at every engine oil change interval. Performing this type of on-site analysis will go a long way towards ensuring the long-term health of your fleet.
In addition to using a test strip and hydrometer/refractometer, we also recommend a periodic analysis of the coolant at an off-site lab. Analysis of the coolant by a lab provides far more information about the coolant than can be gathered from the field tests described above. A lab analysis report will alert you to the presence of wear metals, like Iron and Aluminum, as well as the presence of certain additives, like Boron, Sodium and Potassium. The analysis will also detail the level of nitrites in the coolant, the color and clarity, the pH level, the corrosion inhibitor levels of OAT coolants, the freeze point, the glycol content, the hardness level of the water, the odor, the level of magnetic precipitants, the level of non-magnetic precipitants, the conductivity, and the presence of oil, fuel or foam.
In addition to the all of the added information provided by the lab analysis, it also offers the ability to trend results, so you can easily track the history of the coolant compartment for each machine over time. Trends are easy to observe and can help you to easily note what is happening in the system, as well as the effectiveness of your maintenance practices. For a fleet manager, this kind of information is invaluable, especially when performing post-failure analysis.
For a world-class maintenance organization, periodic coolant analysis at a lab is a requirement. The frequency of lab analysis does not need to be as often as every engine oil change, but at minimum, an annual lab analysis is recommended. Bi-annual lab analysis is recommended for any piece of equipment that runs 2,000+ hours per year.
To summarize: Select the right coolant and the right water source (and dispose of all other coolants onsite); perform daily coolant-level checks, topping off the system as needed with the right coolant; check the radiator for blockage and clean it as needed; check the condition of all system hoses and the tightness of all clamps; check and adjust the tension of all fan belts and replace belts and sheaves when worn; perform onsite testing of the coolant at every oil change interval and adjust the concentration level as needed; and perform offsite lab analysis at least once per year (preferably twice per year).
If you follow these recommendations, you will help to ensure the best cooling system performance for your fleet, which will likely reduce cooling system failures, extend the life of your equipment, and lower your total operating costs.
Castrol’s field engineering team is available to assist you in setting up a cooling system maintenance program for your fleet. If you require more information or assistance with selecting a proper coolant, please contact your Castrol field engineer or sales representative.