LUBRICATION GUIDE
Soluble Cutting Oil: Concentration, Mixing and Stopping Coolant Smell
By the PCG Technical Desk · Updated 27 September 2026
Quick answer: Most soluble cutting oils run at 3–10% concentration. IOCL recommends 5% for SERVOcut S in machining, and leaner mixes for grinding. Always add oil to water, never water to oil. Check concentration daily with a refractometer. Coolant smell comes from bacteria, and the fixes are removing tramp oil, keeping the concentration right, and aerating the sump.
Mixing correctly
- Start with clean water in a clean container.
- Add the oil slowly to the water while stirring (oil into water).
- Top up the machine with pre-mixed coolant, never with neat oil or plain water only.
A 5% mix = 5 litres of oil made up to 100 litres with water (1:19).
Measuring concentration
A hand refractometer gives a Brix reading. Multiply it by the product's refractometer factor (from the supplier's data) to get the concentration. Evaporation raises concentration, and top-ups with plain water lower it, so check it every day.
CNC coolant smell problem: why coolant smells (“Monday morning smell”)
- Bacteria multiply in stagnant, oxygen-poor coolant over weekends.
- Tramp oil (way lube and hydraulic leaks) forms a surface layer that cuts off oxygen and feeds bacteria.
- Low concentration weakens the corrosion inhibitors and biocide.
Fixes
- Skim tramp oil and fix way-lube leaks. A way oil that separates from coolant (Servoway) helps.
- Keep the concentration in range and monitor pH (a falling pH means biological attack).
- Circulate or aerate the sump during long stoppages.
- If it's badly infected, drain, clean with a system cleaner and recharge.
Outside Karnataka? The technical information on this page applies anywhere in India. PCG Business Solutions supplies SERVO in seven Karnataka districts. If you are in another state, send us your requirement and we will point you to IndianOil's authorised channel for your area, or answer any technical question about the grade.
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FAQ
FAQs
Add the oil to the water slowly while stirring, never water into oil. For 5%, use 5 L of oil made up to 100 L with water.
