{ "background": "Industrial machinery fleets are critical capital assets in developing economies, yet systematic methodologies for evaluating their operational efficiency and forecasting performance gains are lacking. In Tanzania, ad-hoc maintenance and utilisation practices hinder productivity and lifecycle management.", "purpose and objectives": "This study aimed to develop and validate a methodological framework for evaluating industrial machinery systems, with the core objective of constructing a robust time-series forecasting model to quantify potential efficiency gains.", "methodology": "A hybrid methodology integrated field data collection from fleet operators with analytical modelling. The core forecasting model employs an Autoregressive Integrated Moving Average with exogenous variables (ARIMAX) formulation: $Yt = \\mu + \\sum{i=1}^{p}\\phii Y{t-i} + \\epsilont + \\sum{i=1}^{q}\\thetai \\epsilon{t-i} + \\sum{k=1}^{r}\\betak X_{k,t}$. Model parameters were estimated using maximum likelihood, and 95% confidence intervals were computed for all forecasts.", "findings": "The ARIMAX model, incorporating scheduled maintenance and fuel quality indices as exogenous variables, produced statistically significant forecasts. Application of the model projected a mean efficiency gain of 18.7% (95% CI: 15.2%, 22.1%) in availability metrics under optimised maintenance regimes. Diagnostic checks confirmed model robustness with no residual autocorrelation.", "conclusion": "The proposed methodological framework provides a rigorous, evidence-based tool for machinery fleet evaluation. The forecasting model successfully quantifies tangible efficiency improvements, moving beyond descriptive analysis to predictive insight.", "recommendations": "Fleet managers should adopt predictive, data-driven maintenance scheduling informed by such models. Policymakers are encouraged to support standardised data collection protocols across the industrial sector to enable broader application.", "key words": "machinery management, predictive maintenance, ARIMAX modelling, operational efficiency, industrial engineering", "contribution statement": "This paper presents a novel application of an AR