Pitfalls of volume %
A freezing point solution made by mixing 50 ml Havoline® XLC + 50 ml water at room temperature in India versus Ghent does not give the same results. The concentration is slightly different.
Why?
You can read the volume of a coolant via a calibrated measuring cylinder (at 20°) in the lab. However, the volume depends on the temperature, see figure below. Generally, higher temperatures cause more expansion of your fluid.
So if the ambient temperature (including your glassware) does not have the same temperature worldwide, a deviation in the volumes occurs (read also the difference in glycol, inhibitors in the final ready mix). Mass is almost the same everywhere on earth and does not influence temperature. Mass (expressed in kg) is the same everywhere, whether there is gravity or not; mass + gravity = weight
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mass is not subject to temperature input
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volume is therefore not preferred to be used!
How to handle examples
Both at the customer and in our lab, you always want the same ratio (concentration of inhibitors) of a ready mix coolant. So the weight percentage is preferable when volume fraction is difficult for measuring, for example, in case of hydrophobic and in case of reactivity of filler to water or another fluid for hydrostatic measuring of filler volume
If the substances react and as a result, you get a soluble substance you end up with a solution of a new substance. In most cases, you have fewer particles to pack so your volume will drop with the mass remaining the same. If additionally, the solvents mix you end up with added effect as in one so the difference can be even higher. This is a mix of chemical and physical reasons.
To achieve uniformity, we work in wt% (mass) and not with volume (or v%).
Practically 50% volume Havoline® XLC will be made by 53 kg of Havoline® XLC + 47 kg of water; In this way you get the same solution (concentration) for every customer, in every lab, regardless of the temperature.
To speak of ratio worldwide (the same concentration of inhibitors), preference is given to wt% / wt%.
FYI: Volume correction at your gas station1
Since 1920s temperature compensation has been used in transactions, were large quantities of petroleum products are measured: pipelines transportation ship loadings, tanks farm transfer.
Electronic temperature compensation has been used for the retail sale of automotive fuel for over 20 years. The words “Volume Corrected to 15 °C” should be visible next to the display on all fuel pumps equipped with an automatic temperature compensator: this benefits consumers and retailers by removing the effects of temperature variation when purchasing and selling fuel.
1 Source: https://www.ic.gc.ca/eic/site/mc-mc.nsf/eng/lm04344.html