In Part II of this series, we explained how to prevent sludge from forming in your heat transfer system. This time, we’ll cover steps you can take if your system has already been fouled.

If you’ve discovered sludge in your system, don’t panic. There are still several effective ways to restore it.

The first step is to test your fluid. A fluid analysis will give you insight into the system’s condition and indicate how severe the issue is. Many major fluid vendors, including Duratherm, provide this service for free, though independent labs can also run key tests like flashpoint, viscosity, and TAN.

Once you have results, take a closer look at the system itself. Sludge often collects in reservoirs and expansion tanks. If possible, inspect these areas for deposits—this will help confirm the scope of the problem.

What are my options?

Manual Cleaning

If the system can be disassembled or accessed, sludge can often be removed manually. Expansion tanks and reservoirs sometimes have access ports for easier cleaning, and lines or hoses can be disconnected and scrubbed with brushes or scrapers.

System Cleaners

When manual cleaning isn’t practical or is too time-consuming, chemical system cleaners can be circulated to dissolve sludge deposits. The right cleaner depends on system size, design, and the level of fouling.

• For light sludge or minor overextension of fluid life, a cleaner/thermal fluid combination like DuraClean works well. It doubles as a system cleaner and operating fluid, making it ideal for preventative maintenance. Smaller systems with frequent oil changes benefit most—using a cleaner every third or fourth change helps keep sludge from building up.
• For larger systems, additive-style cleaners such as DuraClean LSC can be added to existing fluid at 5–10% concentration. These clean gradually while the system remains in production. Some, like DuraClean LSC, can stay in the system indefinitely, while others are used just before a fluid change. Always consult your vendor for specific guidance.
• For heavily fouled systems, solvent-like cleaners such as DuraClean Ultra are the fastest option. These aggressive cleaners can strip away sludge in hours but require draining the old fluid and often flushing afterward. They are best for severely fouled systems that are nearly inoperable.

Because these stronger cleaners act quickly, it’s important to work with both your equipment and fluid provider to choose the most effective and safe method for your application.

If sludge is causing you problems, reach out—we’ll help you find the right solution.