I. Project Background: Frequent Rainy Seasons in Guilin Drive Strong Demand for Sewage Treatment Vehicles. Guilin, located in Guangxi Province, has a subtropical monsoon climate with abundant annual rainfall; during the rainy season, urban flooding and sewage discharge pressure are common. In 2024, a municipal sanitation department launched a procurement initiative for new Dongfeng sewage treatment vehicles to address aging urban drainage infrastructure and emergency sewage treatment requirements. Per publicly available tender information, the project budget was capped at approximately RMB 2.015 million, with three units planned for purchase at an estimated unit price of around RMB 600,000. Following multiple rounds of technical and commercial evaluation, Chengli Special Purpose Vehicle Co., Ltd. secured the contract with its CLW5180TWFD6 model (built on a Dongfeng chassis), delivering three units. Customer feedback highlighted two critical operational challenges: First, Guilin’s hot-humid climate imposes exceptionally high demands on vehicle corrosion resistance and sealing component durability; second, frequent rainy-season operations require sustained high-load performance. Chengli’s solution specifically enhanced the chassis anti-corrosion coating and upper-structure sealing system—ensuring no visible corrosion after five years and extending sealing component service life to eight years, even under ambient humidity exceeding 80%. These features proved decisive in winning the bid. II. Total Cost of Ownership (TCO) Analysis: Comparison Across 5-, 8-, and 10-Year Cycles. During proposal evaluation, the procuring entity prioritized not only initial acquisition cost but also the full lifecycle Total Cost of Ownership (TCO). Based on reference data provided by Chengli and local procurement practices, the following TCO breakdown is presented for the CLW5180TWFD6 model: Cost Item | 5-Year Cycle (RMB 10,000) | 8-Year Cycle (RMB 10,000) | 10-Year Cycle (RMB 10,000) ---|---|---|--- Initial Purchase Cost (per unit) | ~60 | ~60 | ~60 Fuel/Electricity Costs (avg. RMB 40,000/year) | ~20 | ~32 | ~40 Maintenance & Service Costs (avg. RMB 15,000/year) | ~7.5 | ~12 | ~15 Major Overhaul Costs (Year 6 / Year 9) | None | ~8 (Year 6) | ~12 (Years 6 + 9) Residual Value (after depreciation) | ~–20 (residual value: 20) | ~–12 (residual value: 12) | ~–8 (residual value: 8) Total TCO | ~67.5 | ~100 | ~119 Note: Figures above are based on publicly disclosed tender data and after-sales performance data supplied by Chengli; actual values are subject to contractual terms. Fuel consumption estimates assume 200 operational days per year, 8 hours per day. Major overhaul costs primarily cover deep maintenance of the engine, pump assembly, and sealing systems. As shown in the table, the 5-year TCO is lowest—but considering typical municipal fleet replacement cycles, the 8-year horizon represents the standard operational planning period. Thanks to superior anti-corrosion coatings and extended sealing component longevity, the Chengli CLW5180TWFD6 incurs fewer major overhauls within the 8-year window, potentially yielding lower real-world TCO than industry averages. III. Major Overhaul Intervals and Adaptation to Hot-Humid Environments. The major overhaul interval for sewage treatment vehicles is closely tied to operating environment and maintenance quality. Under Guilin’s hot-humid conditions, conventional models often exhibit chassis corrosion, seal degradation, and declining pump efficiency as early as Years 4–5. In contrast, the Chengli CLW5180TWFD6 employs the following design enhancements: • Anti-Corrosion Coating: Chassis and tank utilize epoxy zinc-rich primer plus polyurethane topcoat, with total dry-film thickness reaching 120