Cutting oil which is generally called as Coolant oil in machine shops were parts are machined to desired size and shape using machining centre like VMC, HMC, CNC, Lathe, etc. During this machining process, a large amount of heat being generated between the part and the tool due to friction. To provide lubrication and cooling effect, Cutting oil/Coolant oil is being used. There are two types of cutting oil, 1. Neat cutting oil. 2. Water-soluble cutting oil (WSCO) Neat oil provides good lubricity, which is used for heavy duty machining applications like Gear cutting, Broaching, etc.., and Water-soluble cutting oil provides good cooling effect and appropriate lubricity which is used for Light duty to Medium duty machining applications like Milling, Turning, Drilling, Tapping, Reaming, etc. Neat oil is used 100% in machines and normally does not required any maintenance activity. However, WSCO is generally used in machines with mix in water at 5~10%. Generally, a solution that has water in it always need some maintenance otherwise the microorganism coming from water will destroy the property of that solution. This is the same case for WSCO. If WSCO is in circulation or in agitation, then there will not be much problem. However, if the cutting oil is stagnant for some period like one or two days (mainly during week holidays like Saturday and Sunday) then some care is needed to avoid the WSCO from being decomposed. This is a manageable situation. But if the stoppage is very long, then we should take necessary preventive actions to take care of WSCO, Machine and the Machined parts to avoid huge loss. Following are preventive actions, which need to be carried when there is a long shutdown of your machines running with water-soluble cutting oil (WSCO) 1. Maintain WSCO higher concentration (6~8%) than recommended (4~6%) to strength its bio-stability. This keeps cutting oil healthy for a longer period. 2. To avoid decomposition of WSCO, remove contaminants like tramp oil, sludge and chips from the cutting oil tank. 3. Circulate cutting oil through machine for 30~60 min on daily basis. This will prevent the growth of microorganism. 4. If there is decomposed smell from the WSCO, dump-out the WSCO from the machine immediately. After shutdown period is over, fresh WSCO can be prepared. 5. To avoid rust on machining bed and other expected machine surfaces (generally internal machine areas), the same WSCO at 10% concentration can be sprayed manually on those areas. The same practice need to be followed periodically once or twice a week to keep your machine healthy from rust. 6. To avoid rusting of your parts, apply rust preventive oil and cover it properly to prevent the parts from contaminants like dust and moisture. 7. To avoid white corrosion of Aluminium parts make sure the parts are moisture free and covered properly. If you doubt the presence of moisture, spray dry air or use a de -watering fluid by dipping method to remove the moisture from the parts and cover it properly. Above practice, helps you a trouble free situation when we start our machine after long shutdown.