What would cause series 60 Detroit diesel engine to run at 50 percent hp capacity?

Answer 1

Series 60's have an ECM(electronic control module) that senses problems and executes a power down or derate mode. The sensors check numerous functions of the engine during operation. Low coolant, oil pressure hi and low, and numerous other inputs can cause power down/derate. You need to have the ECM's codes retrieved and that should locate your problem.