Engine manufacturers estimate that poor maintenance of cooling systems causes about 40% of all premature engine failures, and they recommend that mechanics add supplemental coolant additives (SCAs) to protect radiators and engine cylinder liners. SCAs contain chemical buffers to reduce coolant acidity, inhibitors to prevent corrosion, and polymers to coat the metal in the cooling system, which is subject to hard-water scaling. Over time, engine byproducts, operational starting and stopping, and engine liner movement deplete SCAs. Chemical-diffusing coolant filters can counter SCA depletion. The Baldwin BW5200 filter has been field-tested for 3 years and more than 150,000 miles in Cummins M11 and N14 engines. The results showed that SCA distribution was consistent throughout the period. The measured diffusion pattern indicated SCA levels were high enough at the end of the maintenance period to protect the cooling system. Baldwin guarantees that its system maintains a proper chemical balance for a full year or 150,000 miles. The filter uses a high-capacity, high-strength synthetic media to trap contaminants and prevent undissolved particles from entering the engine's cooling system. The flow pattern also ensures that the orifice can't be plugged. Keywords: filter, coolant, radiator, SCA, Baldwin