What must be done to No. 6 fuel-oil due to its consistency?

No. 6 fuel oil, commonly referred to as heavy fuel oil, has a high viscosity and is much thicker than lighter oils. Because of its consistency, it requires heating to lower its viscosity, allowing it to flow more freely and be suitable for use in boilers or burners. Heating the oil before it is pumped into the burner ensures that it atomizes properly during combustion, which is crucial for efficient burning and reduced emissions. This process helps maintain the oil's operability in systems designed for its use and prevents operational issues that arise from using overly viscous fuel.

While filtering is sometimes necessary for removing impurities, the primary requirement due to its consistency is heating. Diluting it with another oil or mixing it with water is not standard practice for No. 6 fuel oil, as these actions could compromise its combustion characteristics and efficiency.