The engine coolant temperature is regulated through the engine sensors plus the engine ECM. This programming can't be altered. An engine derate can occur if the most engine coolant temperature is exceeded. Be sure that the engine is stopped. Inspect all strains and hoses for don or for deterioration. https://perkins-engine-m89-parts18702.thezenweb.com/The-best-Side-of-Perkins-Engine-4-236-Parts-Manual-Catalog-48558238