Coolant concentration log sheet template for each machine sump
Summary
A coolant concentration log sheet needs 4 parts: a sump header, dated readings with units, make-up and additions, and the action taken per reading. It is the record a machine shop's fluid owner or a supplier's service engineer keeps for one sump of water-mix metalworking fluid, filled at every check, with target ranges taken from the fluid maker's data sheet.
UK guidance tells employers to measure concentration with a refractometer and pH every week, check tramp oil weekly with a recommended level below 2%, and measure sump temperature weekly (HSE MW5, 2021).
Dipslide results at or above 10,000 CFU/mL indicate microbial growth, and at or above 1,000,000 CFU/mL indicate poor control that needs immediate action (HSE MW5, 2021).
In Germany, nitrite in used water-mixed coolant is measured weekly, and above 20 mg/L the fluid is changed, partly replaced or given an inhibitor agreed with the maker (TRGS 611, 2007, section 5.3).
The German sample test plan carries fill quantity, make-up water nitrate (max 50 mg/L) and hardness, target concentration and refractometer factor in its header (DGUV Regel 109-003, April 2026).
What is a coolant concentration log sheet for, and who fills it in?
A coolant concentration log sheet is a dated record of one sump's readings, top-ups and actions, filled in by whoever checks the fluid: a machine operator, the shop's fluid owner, or the fluid supplier's service engineer on a visit. Its job is to make a trend visible, so a drift in concentration or pH is caught before it turns into corrosion, odor or skin complaints.
US OSHA guidance on fluid management says the data on fluid condition, laboratory analyses and additions "should be tabulated so that relationships and trends in the data can be spotted" (OSHA Metalworking Fluids manual). UK guidance asks for test records in a table or graph for the same reason, and includes an example table whose header carries location, machine, product, sump capacity, operating concentration and pH ranges and the refractometer correction factor (HSE MW5, 2021).
Those examples are grids. The log sheet on this page turns them into named columns with units, so a reading taken by one person can be read by another without asking what the number meant. One sheet covers one sump: a machine with its own tank, or a central system feeding several machines. Readings from two sumps on one sheet hide both trends.
The editable Excel log and a CSV with the same columns are at the end of this page. For how often to check each reading and how to read the trend, see the guide on how to keep a coolant concentration and pH history per site.
Which columns does a coolant concentration log sheet need, and in what units?
A coolant concentration log sheet needs one column per reading with its unit in the header: date, sump ID, raw refractometer reading in degrees Brix, refractometer factor, concentration in percent, pH, tramp oil in percent, dipslide count in CFU/mL, nitrite in mg/L and temperature in degrees C, then make-up, additions, action and the person who measured.
The table below previews every column of the log with the unit and an example value.
Column | What goes in it | Unit | Example (illustrative) |
|---|---|---|---|
Date | Day of the check | YYYY-MM-DD | 2026-10-05 |
Sump ID | Machine or central system, as in the header | Text | M-07 |
Raw refractometer reading | Value read on the refractometer scale | degrees Brix | 5.0 |
Refractometer factor | Product factor from the fluid data sheet | Number | 1.1 |
Concentration | Raw reading times factor | % | 5.5 |
pH | Strip or meter reading | pH units | 8.9 |
Tramp oil | Free or emulsified foreign oil, method agreed with supplier | % by volume | 1.0 |
Dipslide bacteria | Count read after incubation | CFU/mL | 1,000 |
Nitrite | Test strip or photometric result | mg/L | 5 |
Temperature | Sump fluid temperature | degrees C | 24 |
Appearance and odor | What was seen and smelled | Text | Normal |
Make-up volume | Mixed fluid added since last check | L | 40 |
Make-up concentration | Concentration of the fluid added | % | 2.0 |
Make-up water hardness | Hardness of the water used | Unit of your test kit | 120 mg/L as CaCO3 |
Additions | Additive, type and amount | Text, L or mL | None |
Action taken | What was done because of this reading | Text | Top up only |
Measured by | Name or initials | Text | J.K. |
The concentration row is the one to get right: a refractometer reading is not a concentration until it is multiplied by the product's factor (Blaser Swisslube), so the log keeps both the raw value and the factor.
The header, written once per sump, holds what the rows do not repeat: site, machine or central system, asset reference, sump capacity in liters, fluid product, charge date, fresh-fill pH, target concentration and pH ranges, refractometer factor, titration factor, machining type, make-up water source, make-up water nitrate in mg/L, the hardness unit used and the person responsible. These follow the header of the German sample test plan, which includes the machining type and a titration factor (DGUV Regel 109-003, April 2026).
How do you log tramp oil, bacteria and nitrite readings next to coolant concentration and pH?
You log tramp oil, bacteria and nitrite readings on the same row as coolant concentration and pH, with the same date, because each one changes how the others are read. A concentration reading taken through heavy tramp oil can be wrong, and the German rule for coolant care says high tramp oil content, changed droplet size, dirt or temperature deviations can falsify a hand refractometer result (DGUV Regel 109-003, April 2026).
The table below sets the reference value each reading is compared with, as each source states it.
Reading | Unit and method | Reference value |
|---|---|---|
Tramp oil | % by volume, method from fluid supplier | Kept to a minimum, recommended below 2%, checked weekly (HSE MW5, 2021) |
Dipslide bacteria | CFU/mL, weekly dipslide, sump stirred first | Growth at or above 10,000 CFU/mL; poor control at or above 1,000,000 CFU/mL (HSE MW5, 2021) |
Nitrite (Germany) | mg/L, test strips or photometry | Weekly; up to 4 weeks after three readings in a row below 10 mg/L if checks are documented, back to weekly above 10 mg/L; action above 20 mg/L (TRGS 611, 2007, section 5.3) |
pH drop | pH units, against fresh fill | Above 0.5: maker's measures; above 1.0: exchange and clean if needed (DGUV Regel 109-003, April 2026) |
The dipslide row is the one most logs get wrong: write the count in CFU/mL, since UK guidance reads growth from 10,000 CFU/mL and poor control from 1,000,000 CFU/mL (HSE MW5, 2021).
Write the measured value, never "OK" or a tick, because a tick cannot show a trend. Where a reading is skipped, write "not measured" so the gap is visible. Not every fluid needs every column: one coolant maker notes that dipslide tests make no sense for its bio-concept fluids, where bacterial growth is intended (Blaser Swisslube).
How should a coolant log record make-up volume, make-up water and additions?
A coolant log should record every top-up as a volume in liters with the concentration of the fluid added, the water it was mixed with, and every additive by type and amount, on the row of the check where it happened.
UK guidance says water-mix fluids evaporate and become more concentrated in use, so it tells employers to "top up only with fluid below recommended concentration" (HSE MW5, 2021). Logging make-up concentration shows whether that was done. The US OSHA manual asks that all system additions, including fresh biocides, fluid additives or concentrates and water used to make up fluid loss, be controlled and recorded by a designated person (OSHA Metalworking Fluids manual).
Record the make-up water as well. UK guidance tells employers to check input water for hardness, pH and bacteria (HSE MW5, 2021). In Germany, water used to mix or top up the fluid must not exceed 50 mg/L nitrate (TRGS 611, 2007, section 5.2). A coolant maker notes that with hard water and high evaporation, hardness can build up fast and destabilize the emulsion (Blaser Swisslube), so a hardness value per top-up shows when to switch water.
For additions, the German rule recommends recording the biocide type, its concentration during use allowing for top-ups, and the maximum concentration set by the biocide maker (DGUV Regel 109-003, April 2026). Add biocide only at the doses your supplier recommends, and only after the other fluid measures have been tried (HSE MW5, 2021).
How do you fill in the coolant log sheet at each check?
You fill in the coolant log sheet at each check in six steps, so readings from different people stay comparable.
Take the sample from the same point in the sump, wearing the gloves and eye protection named in the fluid's safety data sheet (SDS). UK guidance tells you to stir the sump before a dipslide test so tramp oil does not coat the slide (HSE MW5, 2021).
Read the refractometer and write the raw value in degrees Brix, then the factor, then the concentration as raw reading times factor (Blaser Swisslube).
Read pH with strips or a meter. Meter electrodes foul quickly with tramp oil, so the German rule recommends indicator strips in steps of 0.2 or 0.3 units, not universal strips (DGUV Regel 109-003, April 2026).
Record tramp oil, temperature, nitrite where required, and the dipslide reference, entering the count when the slide has been read after the incubation the slide supplier specifies (HSE MW5, 2021).
Write the make-up volume, its concentration, water hardness and additions since the last check. Add biocide only at the dose your supplier recommends and as its label and SDS state (HSE MW5, 2021).
Write the action this reading caused, even "none", and your name.
Compare the row with the header's target ranges before leaving the machine. A value outside the range needs an action, or a note of who was told. If a third party does the checks, UK guidance tells the employer to review the results and the remedial actions taken (HSE MW5, 2021).
What does an illustrative filled coolant log sheet look like?
An illustrative filled coolant log sheet for one sump over four weekly checks shows concentration falling, tramp oil rising and one corrective action, with every value and its unit on the row of the check. All values below are illustrative and describe no real machine, product or site.
The table below is the illustrative log for sump M-07, product factor 1.1, target concentration 5 to 7% and target pH 8.6 to 9.2, fresh-fill pH 9.2.
Date | Readings (illustrative) | Make-up and additions (illustrative) | Action (illustrative) |
|---|---|---|---|
2026-10-05 | 5.5 degrees Brix, 6.1%, pH 9.0, tramp oil 0.5%, 22 degrees C | 40 L at 2%, hardness 120 mg/L as CaCO3 | None |
2026-10-12 | 5.0 degrees Brix, 5.5%, pH 8.9, tramp oil 1.0%, 23 degrees C | 60 L at 2% | Watch concentration |
2026-10-19 | 4.4 degrees Brix, 4.8%, pH 8.6, tramp oil 2.5%, dipslide 1,000 CFU/mL | 50 L at 2% | Skim tramp oil; correct concentration as the supplier advises; check way oil leak |
2026-10-26 | 5.2 degrees Brix, 5.7%, pH 8.8, tramp oil 0.8%, 23 degrees C | 45 L at 4% | Leak fixed by maintenance |
The key row is 2026-10-19: concentration fell below the 5% target while tramp oil passed 2%, and the pH had dropped 0.6 units from the fresh fill, past the 0.5 at which the German rule refers to the maker's measures (DGUV Regel 109-003, April 2026).
Read down the columns and the cause shows. Make-up at 2% kept diluting the sump while tramp oil rose, so the concentration fell week by week. Without the make-up column, the falling concentration would look like a fluid problem rather than a top-up habit and a leak (illustrative interpretation).
How long should coolant log sheet records be kept, and where?
Coolant log sheet records should be kept for at least five years under UK guidance and at least three years under the German rule for coolant work, which explicitly recommends keeping them longer (HSE MW5, 2021; DGUV Regel 109-003, April 2026). A site working to both would keep the longer period.
The two sources serve the same purpose with different periods. The German rule says the records also help to learn about long-term changes later (DGUV Regel 109-003, April 2026), and a trend over several fluid charges is exactly what a short retention throws away. Keep the old sheet when a sump is recharged, and start a new sheet with the new fill date and fresh-fill pH, so two charges are not read as one trend.
Keep the sheet where both the shop and the supplier can read it. A paper sheet at the machine is easy to fill but hard to trend; a spreadsheet is easy to trend but often lives on one laptop. The German IFA coolant portal offers its own coolant monitoring sheet as an Excel file (DGUV IFA), which shows how common the spreadsheet form is.
Whatever the medium, keep the safety data sheet of each fluid and additive with the log. The German rule notes that REACH requires users to keep safety data sheets available for at least ten years after last use (DGUV Regel 109-003, April 2026).
When does a per-machine coolant log sheet not fit?
A per-machine coolant log sheet does not fit neat cutting oils, large central systems run on laboratory analysis, or sites where the fluid maker supplies its own monitoring program with its own forms. The columns on this page are for water-mix metalworking fluids checked at the sump with field tests.
Neat oils need a different set of checks, since concentration, pH and nitrite do not apply to them. A central system feeding dozens of machines is usually managed on laboratory reports that add values such as emulsion stability, corrosion tests and biocide levels, which the US OSHA manual lists among the factors a fluid manager may track (OSHA Metalworking Fluids manual). A per-machine sheet still works there for the daily field readings, but the decisions rest on the laboratory data.
Jurisdiction changes the required columns. The nitrite column comes from the German rule (TRGS 611, 2007, section 5.3) and is optional elsewhere unless your fluid maker or your own risk assessment asks for it. The dipslide thresholds come from UK guidance (HSE MW5, 2021); other countries and fluid makers may use other methods. Target ranges always come from the fluid's own data sheet, not from this template.
In Lubinpla, the same readings can be kept in a project's condition measurement history and product usage records, and its work log bulk import takes the CSV version of this log but not the Excel file. Add or remove columns in the Excel log to match the checks your site actually runs.