A clean metalworking fluid performs better and lasts longer than a dirty fluid. When recharging an individual machine or central system fluid tank, a cleanout of the tank is beneficial so that the fresh charge of metalworking fluid can perform with maximum efficiency.

If not removed, accumulated shop waste, metal swarf, oil, mold growth, and pockets of bacteria cause deterioration of the fresh mix. In a new system, construction debris in the trenches and tanks, the chemical waste such as welding flux, must be removed from the assembly of steel trenches. If the trenches are constructed of cement, a good cleaning helps to season them.

The cleanout, therefore, is an essential first step. It insures that your metalworking fluid has an “even chance” to give maximum performance with a minimum number of problems. The following cleanout procedures should be used when ever possible, while no operators are producing parts.


  1. Drain the entire central system or individual tank.
  2. Remove all metal swarf and other debris from sumps, return trenches, oil pans, and filtration units.
  3. Fill the system or tank with water sufficient to circulate through all lines and machines. Warm water is desirable, but is not absolutely necessary.
  4. Add a sump cleaner as recommended by the supplier and use as recommended.  Typically, a sump cleaner will require the cleaning fluids to circulate from 2 to 8 hours. During this period of circulation, brush all trenches and filter elements; scrub machines and oil pans.
    WARNING! Appropriate Personal Protective Equipment such as gloves or face shields must be worn by maintenance personnel during this operation because some cleaners are highly alkaline and prolonged contact with the skin may cause irritation.
  5. If possible, steam clean areas where suspected accumulation of swarf, oil, or both may not have been removed by the cleaner.
  6. When the physical cleaning is complete, drain the cleaner mix from the system.
  7. Refill with enough fresh water to circulate throughout the system or tank(s) so that all traces of cleaner and swarf are removed. Drain all lines and sumps. If the rinse water is still dirty, rinse a second time.  Never use plain water for extended period of time as this may cause corrosion of the machine, reservoir, tooling or other parts of the system.  It is sometimes advisable to add a weak dilution of the product to be used while circulating.  For example, a 2% dilution of the metalworking fluid can help to “pre-condition” the system to better prepare for the fresh charge.  Always drain this diluted product before charging the system for use.
  8. Charge the system or individual tank(s) with the required amount of water.
  9. Add a fresh charge of the appropriate product at the recommended concentration.
  10. Circulate through the system to insure proper mixing before production starts. In precision grinding systems, circulate the fresh charge until it reaches room temperature. Otherwise, size control problems may be encountered by the first production shift.

Sometimes it is not possible to drain the system because of production demands or a manpower shortage. However, try to incorporate as much of the cleanout procedure as possible into one of the alternate methods (during shutdown or during production) shown below to achieve a good cleanout.

With Used Fluid- During Shutdowns

After production stops, add the supplier-recommended volume of cleaner concentrate to the fluid in the machine reservoir or central system. Circulate the mixture for the amount of time recommended by the supplier to insure proper cleaning, through all lines and machine tools. Drain, rinse, and recharge with a fresh cleaner mix.

With Used Fluid- During Production

Not recommended for individual machines unless carefully supervised. During production, add the supplier-recommended cleaner to the dirty fluid in the machine reservoir or central system. Circulate the mixture for 4 – 8 hours through all lines and machine tools. Drain, rinse, and recharge with a fresh cleaner mix.  It may also be possible to add small amounts of cleaner during production without dumping, but special precautions should be taken.  Consult with your supplier for the appropriate recommendations.

Still having problems?

Back to Parts Washing