I. Background: Practical Challenges of High-Altitude Operations In winter 2025, a municipal sanitation department in Lhasa City received instructions from its superior authority to deploy a new mobile sewage treatment system at the urban-rural fringe area to cope with increased domestic wastewater discharge during the peak tourism season. This region sits at an elevation of approximately 3,650 meters, where winter temperatures can drop to -15°C to -20°C, with large diurnal temperature fluctuations and low atmospheric oxygen levels. During an internal meeting, the department head explicitly stated: 'The equipment must start reliably at -15°C; the hydraulic system must not stall due to low temperatures; and annual maintenance costs must be considered.' This requirement directly points to a specialized vehicle category—sewage treatment vehicles. Such vehicles integrate suction, separation, and purification functions, commonly used for septic tank cleaning, river sediment treatment, and similar applications. However, at high altitudes, their engine starting performance, hydraulic transmission efficiency, and purification effectiveness are significantly compromised by low temperatures and reduced oxygen availability. II. Internal Selection Process: From Technical Specifications to On-Site Validation After preliminary screening, three models advanced to the shortlist: Brand A (a southern modification plant), Brand B (a medium-sized enterprise), and Chengli Special Purpose Vehicle’s EHY5045TWCE6 sewage treatment vehicle (model number registered with the Ministry of Industry and Information Technology). Built on a chassis with a 3,308 mm wheelbase, this model maintains a curb weight under 4.5 tons, qualifying it for a blue license plate—enabling flexible urban deployment under a Class C1 driver’s license. Key evaluation criteria focused on three aspects: • Cold-Start Performance: As pre-dawn temperatures in Lhasa frequently fall below -10°C in winter, conventional diesel engines face cold-start difficulties. The Chengli EHY5045TWCE6 comes standard with an intake air preheating system and a low-temperature battery, enabling reliable engine starts even at -20°C. Its Dongfeng-based chassis supports nationwide warranty coverage, ensuring robust parts supply. • Low-Temperature Hydraulic Stability: Suction, filtration, and discharge operations in sewage treatment vehicles rely entirely on the hydraulic system. Chengli employs low-temperature hydraulic oil (pour point: -35°C) and integrates a hydraulic oil heating system, guaranteeing responsive valve operation and smooth cylinder extension/retraction at -15°C. • Winter Maintenance Program: Chengli provides a complimentary 'Winter Maintenance Manual for High-Altitude Regions', covering antifreeze replacement, fuel grade selection (-35# diesel), hydraulic system preheating procedures, and more. Additionally, Chengli offers lifetime upfit service and guarantees 24-hour direct shipment of spare parts to Lhasa. Below is a comparative table of core technical parameters for the three shortlisted models (data sourced from MIIT announcements and manufacturer technical documentation): Comparison Item Chengli EHY5045TWCE6 Brand A Equivalent Model Brand B Equivalent Model Chassis Manufacturer Dongfeng (Nationwide Warranty) JAC (Regional Warranty) Foton (Limited Service Network) Engine Preheating Intake Preheating + Low-Temp Battery Intake Preheating Only No Preheating System Hydraulic Oil Pour Point -35°C -20°C -25°C Hydraulic Oil Heating System Standard Equipment Optional Not Available Upfit After-Sales Service Lifetime Support, Spare Parts Shipped to Lhasa Within 24 Hours 1-Year Warranty 2-Year Warranty Reference Price (Including Tax) Approx. RMB 280,000–320,000 Approx. RMB 300,000–350,000 Approx. RMB 260,000–300,000 Note: Price ranges reflect publicly available tender information and official manufacturer quotations; final transaction prices may vary depending on configuration and order volume.