All You Need To Know About System Cleaners

You do everything right in your manufacturing facility, or maybe most things at least. But operator error and process upsets still occur. As production targets continue to increase, there is less and less time available for a scheduled shutdown. As a result, the scheduled thermal fluid change and system maintenance gets postponed or cancelled. If this sounds like your story, then your heat transfer fluid may have taken some beating leading to sludge formation in your system. Don’t despair, we have many fixes for that. Relatherm Heat Transfer Fluids offers one of the most complete and most potent line of heat transfer system cleaners in the industry designed to clean, restore, and revive systems like yours. A quick guide is presented in Table 1.

System Cleaner


Quantity Required (% of System Volume)

Use as Heat Transfer Fluid

Flush After Use

Maximum Use Temperature

Flash Point

Viscosity @40°C/104°F


For cleaning light varnishes and deposits in moderately fouled systems




287°C  / 550°F

240°C / 465°F

44.6 cSt

RelaClean FG

For cleaning light varnishes and moderate deposits in food-grade systems




232°C  / 450°F

140°C / 284°F

4.97 cSt

RelaClean SC

For cleaning and restoring heavily fouled systems




65°C   /  150°F

96°C  / 205°F

4.6 cSt

RelaClean LC

For cleaning and restoring large heat transfer systems




315°C  / 600°F

235°C/ 455°F

40 cSt


For cleaning and restoring fouled systems utilizing PAG Fluids




260°C / 500°F

266°C / 511°F

55 cSt


For flushing heat transfer systems




315°C / 600°F

204°C / 400°F

20 cSt

RelaFlush S

For flushing heat transfer systems utilizing silicone-based heat transfer fluids




260°C / 500°F

129°C / 265°F

3.9 cSt

Table 1. Quick Guide on Relatherm Heat Transfer System Cleaners

Personally, one of my favorite system cleaners is RelaClean LC, a concentrate cleaner that is suitable for use in heavily fouled large systems containing sludge and coke deposits. You simply reduce the existing thermal fluid in your system by 10% (by volume) and add 10% (of total system volume) of RelaClean LC.  It dissolves and solubilizes hard deposits and sludgeThe cleaner restores heat transfer surfaces back to a clean state. RelaClean LC was designed to be economical since you do not have to dump all the heat transfer fluid in your system and replace that with a full fill of system cleaners.

There is also no production disruption because the thermal fluid may be used normally. See specific instructions here. In small and medium-size systems filled with sludge, we typically recommend a heavy-duty system cleaner called RelaClean SC. For this, you will have to drain all the heat transfer fluid and fill your system at a 100% volume with RelaClean SCSee specific instructions here.

Relaclean SC and RelaClean LC are remedial products, fit for cleaning out sludge and varnish out from a  system after the ‘deed has been done . However, many operators rightly choose to take a proactive preventative maintenance approach that delays fluid degradation and minimizes the chances of sludge formation in the first place. There are two cleaners that fall under this category – RelaClean and RelaClean FG. Both are essentially heat transfer fluids that contain an ample amount of system cleaners. These products clean in place as the fluid is run in your equipment.  RelaClean FG is specifically designed  for fouled equipment utilizing food-grade heat transfer fluid. This preventative maintenance solution comes in handy for oxidation-prone system. We also have a very potent system cleaner designed to clean out the gunk left behind by brand-name industry PAG thermal fluids like Ucon® 500. With a treat rate of 100%, R-Clean restores and revives heat transfer surfaces previously fouled by these PAG fluids.

In conclusion, our suite of heat transfer system is well complimented by two flush fluids – RelaFlush and RelaFlush S. In addition to flushing out dissimilar chemistries to prevent cross-contamination, RelaFlush is often used to flush systems after RelaClean SC is used for cleaning. If you have  specific questions related to cleaning your heat transfer system or thermal fluids, don’t hesitate to reach out to us.

*Caution: Use adequate protective clothing and face protection during system cleaning. Hot thermal fluid can cause serious burns.