Compressor Oils / 4 min
Critical Points in Compressor Oil Selection
In compressed air systems, compressor oils don't just lubricate rotating parts — they also help seal air and carry away the extreme heat generated during air compression. Choosing the wrong compressor oil lowers energy efficiency and leads to clogged separators.
Published by: Rotek Technical Content Team
Content is published based on manufacturer technical documentation and equipment requirements as the basis for final selection. This is general guidance and does not replace equipment-specific manufacturer approval.
Review our editorial guidelinesTable of Contents
- - Choosing Oil by Compressor Type
- - Oxidation and Carbon Deposits
- - Operating Temperature and Service Interval
- - Separator Life and Foaming
Choosing Oil by Compressor Type
Rotary screw compressors are systems where oil is compressed together with air, requiring good water/air separation (demulsibility). Reciprocating compressors, exposed to higher compression temperatures, need thicker oils (generally ISO VG 100 or 150) that don't form carbon deposits (coking).
Oxidation and Carbon Deposits
Compressor oil, in constant intense contact with air at high temperatures, tends to oxidize quickly. Oxidation darkens the oil, raises its viscosity and can lead to stubborn carbon deposits that pose a fire risk at the valves.
Operating Temperature and Service Interval
While standard mineral compressor oils offer a service life of 2,000 to 4,000 operating hours, PAO or synthetic ester-based oils can last 8,000 to 12,000 hours. However, if compressor discharge temperature rises above 90°C, the planned oil life shortens significantly.
Separator Life and Foaming
The quality of the anti-foam additives in compressor oil determines its air-separation performance. If the oil foams excessively, it escapes into the compressed air line, causing premature clogging of air/oil separators and contamination of line filters.
Frequently Asked Questions
Can engine oil or hydraulic oil be used in a compressor?
Absolutely not. Detergent additives in engine oils hold moisture (creating an emulsion), and hydraulic oils are not suited to the air-release and oxidation-resistance demands of high-pressure air compression.
How do we know compressor oil life has ended?
Oil life is tracked via the compressor's running-hour counter. However, the oil turning tar-like in color, a burnt smell, and an increasing separator pressure differential are urgent signs that the oil needs changing.
Is ISO VG 46 or 68 used in a screw compressor?
This depends on the compressor manufacturer's (OEM) specification and ambient temperature. ISO VG 46 is used in cooler climates and certain designs, while ISO VG 68 is more common in temperate/hot climates and general screw systems.
Why does oil consumption (or oil carryover) increase?
If the compressor is constantly running too hot, the oil evaporates; if the wrong, cheap (foaming) oil is used, the separator can't do its job fully and oil escapes into the system with the air.