Many of today's heavy-duty engine problems can be traced directly or indirectly to the cooling system. Dirt, oil, corrosion or inhibitor overdose in a cooling system can lead to such problems as cavitation and deposits, which result in leakage, reduced heat transfer and, in extreme situations, restricted coolant flow. Maintaining heavy-duty cooling system cleanliness is an important preventative maintenance practice.This paper describes a unique Multi-Stage Regeneration Process (MSRP) based on filtration and dual-resin deionization. Complete corrosion and performance test results on the reinhibited finished coolant are included. This multi-stage process removes inhibitors and contaminants in both ionic and particulate form and at the same time eliminates the disposal problems associated with used coolant.