Standby diesel generator sets (gen-sets) are used worldwide to provide a backup electricity supply should the mains supply to a site be lost. The diesel engine can start rapidly and the gen-set can begin supplying power within 20–60 s. Traditional commissioning of a gen-set is performed when the engine is at its normal ‘hot’ operating temperature. Unless a jacket water heater is used, once the gen-set is shutdown the engine will cool to the ambient temperature, and following start-up the load acceptance performance will be lower than when it was in a hot operating condition. A novel voltage regulator design which utilises engine temperature as a supplementary control input is presented, providing an improvement in a gen-set's cold load acceptance performance without compromising its standard hot performance. The new voltage regulator design is tested on a commercial diesel gen-set to demonstrate the optimised load acceptance performance.