ASTM D5931 Standard Test Method for Density and Relative Density of Engine Coolants by Digital Density Meter

Get Certified ASTM D5931 Testing for Reliable Engine Coolant Density Verification

Certification confirms that engine coolant concentrates and aqueous coolants meet the corresponding ASTM D5931 requirements, such as density within specification limits for the type of product. ASTM D5931 certified testing determines a coolant’s density before manufacturers accept it for automotive, heavy-duty, or industrial distribution. Testing and certification verify compliance with ASTM D5931 requirements and minimize the possibility of formulation errors in product release to market. 

• Material type: Glycols, glycerin, heat transfer fluids, engine coolant concentrates, and aqueous engine coolants. 
• Purpose: Determine the density and relative density of a substance. 
• Properties evaluated: Density and relative density. 
• Testing Method: A sample is placed in an electronic density measurement device, and the density is derived from the frequency of oscillation of a U-tube that is filled with the fluid. 
• Result: The density is measured in grams per milliliter (g/mL) or kilograms per cubic meter (kg/m³). 
• Test Limitations: The test method should not be used for samples which are so dark that technicians are unable to ensure that there are no air bubbles in the sample cell. 
• Use conditions: Sample temperature directly influences density; therefore, technicians compare results to a baseline temperature (usually 25°C, 20°C, or 15.6°C). 
• Applications: Automotive coolant quality control, heat transfer fluid characterization, glycol concentration checking, and heavy-duty engine coolant verification.

What are the Uses of ASTM D5931 Testing?

For engine coolants and other related fluids, ASTM D5931 testing allows laboratories to quickly and accurately characterize the fluid by measuring its density. Engineers then apply the results to determine the volume of products at standard temperatures and to confirm the formulation of those products. This standard-

• Determines the concentration and specific gravity of engine cooling solution.
• Artificially uses the frequency of oscillation of a U-tube to determine the mass of fluid.
• Calculates the concentration of aqueous coolants and glycols.
• Helps to translate measured volumes to standard reference temperatures.
• Assists in the comparison of formulation between batches of coolants.
• Helps with quality control of manufacturing and blending of coolants.
• Helps select heat transfer fluids for a specific application. 

What Materials Can Be Tested Under ASTM D5931? 

ASTM D5931 covers glycols, glycerin, heat transfer fluids, engine coolant concentrates, and aqueous engine coolants. Common examples are ethylene glycol- or propylene glycol-based coolants, pre-diluted antifreeze products, and industrial heat transfer fluids. This method is not recommended for samples that are so dark that it is impossible to confirm the absence of air bubbles in the sample cell. 

Why is ASTM D5931 Important? 

ASTM D5931 is important because it provides a quick and accurate test method for a basic physical property that, together with other properties, is used to fully describe the coolants used in engines. The manufacturers use these measured density values to convert the volumes to a standard reference temperature for uniformity in quality control, formulation, and commercial business purposes. 

ASTM D5931 Testing Process and Data Collection

Testing starts with calibrating the digital density meter at the desired test temperature using a series of fluids with known density. The technician then homogenizes the coolant sample and introduces it into the oscillating U-tube cell using a syringe or automatic sampler. The technician then visually checks for any air bubbles in the sample. The instrument keeps the sample at the desired test temperature and also records the frequency of the vibrations of the U-tube, which changes with the mass of fluid in the tube. Finally, the instrument converts this frequency to a density value, and the technician writes this value down, in this case grams per milliliter or kilograms per cubic meter (kg/m³) at the specified reference temperature. 

Common Challenges and Troubleshooting

High readings of density are often due to air bubbles being trapped in the sample cell, which means that the U-tube is oscillating a smaller mass than normal. The problem becomes exacerbated with dark coloured samples, and the standard does not cover samples that are darker than what technicians are confident of detecting the absence of bubbles. Density changes as a function of sample temperature also cause changes in reading, and temperature instability during measurement also causes changes in reading. Laboratories solve these problems by introducing samples into the gases at low rates to prevent the introduction of air, ensuring a complete temperature equilibration before reading, and carefully cleaning the cell between each sample. 

• The laboratory reports the density in grams per milliliter or kilograms per cubic meter at the test temperature.
• The technician determines the fluid type of the sample, which can be a concentrate, an aqueous coolant, a glycol, or a heat transfer fluid.
• The analyst measures density under the stated temperature conditions and correlates it with the tested fluid and formulation.
• When interpreting density results, the engineer takes into account the test temperature, sample color, and the possibility of air entrainment.
• Engineers use these measured densities to transform volumes to standard reference temperatures and validate coolant formulation. 

Link to ASTM D5931