Colour shifting or fading

Feedback about colour shifting or fading is often given from the field. Understanding what is specifically causing the observed issue requires insight in the engine or system conditions & dynamics, running hours, materials used (metals and non-metals), previously used product, the products’ initial colour, dilution rate, etc… This information ensures Arteco’s specialists can make a sound assessment of the potential causes for the colour change, which can be multiple.

A dye is a colouring agent added to the coolant to differentiate from other functional fluids or lubricants as well as to make its presence in the cooling system visible. A dye has no performance purpose which means that a colourless coolant will equally perform as a coloured one.

The dyes used in Arteco coolants are selected in close cooperation with the dye manufacturer. The selection is based on chemical structure, functional groups and composition, colour and compatibility with the targeted coolant. We only select robust and stable dyes in order to avoid discolouration as much as possible. Before adding the dyes to the coolant, they passed a demanding test program such as high temperature stability and static/dynamic corrosion testing under multiple conditions (e.g. different water qualities, addition of corrosive salts, addition of metal contamination, etc…). Finally, depending on the OEM approval program, the colour stability is ultimately screened in a field test.

Despite having passed thorough lab testing, colour fading in the field is still possible due to the complexity of cooling system components and ever-changing operating conditions. As a result, evaluation in the field remains the ultimate proof.

When a coolants’ colour is visually off, different reasons might apply.

1. It can be as simple as a cosmetic incompatibility upon mixing two different coloured coolants (orange and blue for instance). The comparison can be done against a colour standard. Getting detailed info on the separate dyes present in the coolant or the coolant mixture can be obtained by plotting a colour scan of the sample. The higher the active dye concentration the stronger the peak signal.

    

2. A dilution effect or the presence of solid particles causing the colour to appear different. Overdilution can turn the coolants’ colour less visible. In case solid contamination is present such as corrosion metals or other physical particles, filtration might turn the colour back to normal. For a sample directly taken from a system the appearance might change completely after a while upon precipitation of solid contamination. Analysis of the filtered solids will shed some light on the origin.

    

3. Contamination with foreign fluids such as fuel, lubricating oil or grease can also be the reason of colour change. The obtained mixture shifts into different layers following a difference in density. Decantation of the less dense fuel/lubricant fraction and subsequent analysis allow determination of the nature and type.

    

4. If physical contamination or cosmetic incompatibility is absent, a change in chemical structure of the dye – often under the influence of different facts simultaneously taking place – is responsible for the colour change. This case needs to be considered as a real colour fading or dye instability, since the electronic structure of the atoms of the active dye molecule is altered.

In order to find out what exactly caused the dye to fade, a detailed test program is required. A combination of physico-chemical tests as well as advanced analytical tests are run delivering a whole set of data which need to be analysed to establish causal links.