Dirt attached on air-side fins of air coolers are a mix of carbonaceous particles such as soot and oil mist of unburned fuel components. 
Carbonaceous particles can be removed by Alkaline Cleaners Part No. RXSOL-16-1040-025 ( www.rxmarine.com/alkaline-air-cooler-cleaner ) and oil mist can be removed by oil based cleaners. However, it is very difficult to remove the mix of these substances. If you use an alkaline cleaner, oil will repel the water based alkaline cleaner; if you use oil based cleaner, carbonaceous particles will get in the way and stop oil from being removed.

This cleaners designed to remove both carbonaceous and oil simultaneously. An effective cleaning method is to immerse one side to remove the loose stains first, and then immerse the other side. This method can efficiently remove dirt and prevent swollen dirt peeled from fins from blocking the spaces between fins.

Dirt in tubes of seawater side

White scales attached on the seawater side of air coolers of many vessels. We found that in most cases, the main component of the scales is calcium carbonate and there is also a small amount of calcium sulfate. Therefore in most cases, if you dissolve the calcium carbonate the scales will be removed.

However, if the amount of scales is large enough to block the tube, the cylindrical scale will usually have calcium carbonate on the outside (the side that is in contact with tube) and calcium sulfate in the center (part that seawater passes through). Calcium sulfate is easier to be formed when the temperature goes higher.

When the amount of scales increases, the contact area of scale and cleaner is very small and a longer time of dissolution is required. Calcium sulfate cannot be dissolved by an acid cleaner.