Abstract <p>Heavy crude oil, due to its higher viscosity, poses challenges for transportation via pipelines and production from reservoirs. This study aimed to evaluate the effectiveness of dilution and heating methods in assessing the influence of organic solvents on the heavy crude oil properties. Specifically, it focused on viscosity, API gravity, Conradson carbon residue, and sulfur content, as well as viscosity reduction. Heavy crude oil samples were collected from the oil field of Al-Ahdab. The heavy crude oil was treated with various fractions of n-heptane and toluene, along with a mixture of 50% <i>n</i>-heptane and 50% toluene, added at concentrations of 5, 10, and 15 wt % at a temperature of 25°C. The study also examined the impact of temperature, varying from 25 to 50°C, on viscosity. Results indicated that diluting heavy oil samples with toluene produced the most favorable results at the 15% addition compared to the other solvents used. Heavy crude oil viscosity decreased to 26.221 cst, with a density of 847.9 kg/m³ and an API gravity of 31.755. Additionally, the total sulfur content was reduced to 3.2%, and the Conradson carbon residue decreased to 7.9‒6.3%. The study further analyzed the influence of temperatures from 25 to 50°C, considering solar heating as a low-cost renewable energy source, on viscosity and viscosity reduction percentage (VR %). It was found that as temperature increased, the viscosity of heavy crude oil decreased. This reduction was more pronounced with higher solvent concentrations: 15 &gt; 10 &gt; 5%, leading to reductions of 74.5, 60.4, and 52.3%, respectively. As a result, the heavy crude oil became lighter and more efficient than the original crude oil, with toluene showing superior performance compared to the other solvents in terms of overall characteristics.</p>