Castair CAST-LUBE Full Synthetic Rotary Screw Compressor Oil — 1 Gallon
The GA4000 is the factory-specified lubricant for Castair rotary screw compressors. This is not a general-purpose compressor oil — rotary screw compressors have fundamentally different lubrication requirements than piston compressors, and the GA4000 is engineered specifically to meet those requirements. At 83.16 per gallon, it is the most expensive oil in the Castair lineup, and the service interval reflects that: the GA4000 is rated for 1 year or 4,000 hours, which is a dramatically longer service life than any piston compressor oil in the CAST-LUBE range.
Why Rotary Screw Compressors Need a Different Oil
Rotary screw compressors inject oil directly into the compression chamber. That oil lubricates the male and female rotors, seals the clearances between them, and carries heat away from the compression process. It then gets separated from the compressed air downstream and re-circulated. Because the oil is continuously in contact with hot compressed air under load, it faces oxidation stress that piston compressor oil does not. It also has to stay compatible with the oil separator, the downstream oil filter, and in some cases, the air quality at the outlet.
Using piston compressor oil in a rotary screw — or worse, automotive oil — will shorten separator life, cause varnish and sludge buildup on the rotors and in the cooler, and potentially void the warranty. The GA4000 is formulated to resist oxidation, inhibit varnish formation, and remain stable through the full 4,000-hour service life.
GA4000 Full Synthetic Features
- Full Synthetic Base Oil: Provides superior oxidation resistance and thermal stability compared to mineral or semi-synthetic oils — critical for rotary screw applications where oil is always hot and under load
- 4,000-Hour Service Rating: One year or 4,000 hours between changes — reduces maintenance downtime and per-hour lubrication cost significantly compared to piston compressor oils
- Anti-Varnish Formulation: Resists the varnish and sludge deposits that develop on rotors, in coolers, and in oil separators when inferior lubricants are used in rotary screw applications
- Separator Compatible: Will not degrade oil separator media prematurely — changing to off-spec oil is a common cause of premature separator failure
- Factory Approved: Castair's specified lubricant for all CASTAIR rotary screw compressors
- Foam Resistant: Does not aerate under the rapid circulation of a rotary screw injection system
GA4000 vs. Other CAST-LUBE Oils — Which One Does Your Compressor Use?
Castair makes specific oils for specific compressor types. The differences matter:
Rotary Screw Oil
- GA4000 — Full Synthetic, 1 Gallon — THIS PRODUCT: For Castair rotary screw compressors. 1-year or 4,000-hour service interval. Do NOT use in piston compressors.
- FG4000 — Full Synthetic, 5 Gallon: Same formula as GA4000, bulk quantity for high-volume shops or multi-unit installations.
Piston Compressor Oils (Not for Rotary Screw)
- GA10W30 — Full Synthetic 10W30, 1 Gallon: For Castair piston compressors. 800-hour or 8-month service interval.
- GA5W30 — Semi-Synthetic 5W30, 1 Gallon: For Castair piston compressors. 400-hour or 4-month service interval.
Varnasolv Rotary Cleaner
Castair also offers Varnasolv, a rotary varnish cleaner. If you are switching to GA4000 from a different brand of oil and suspect varnish buildup, mix Varnasolv at 10%, run 50 hours, then drain and replace with fresh GA4000 and new separator filter. Do not skip the separator filter change — old varnish contamination will shorten the new filter's life.
When Does a Shop Need the 5-Gallon vs. 1-Gallon?
The GA4000 1-gallon is the right call for single-unit rotary screw installations where you change oil annually. For shops running multiple rotary screw units, or where the compressor holds more than a gallon of oil per change, the FG4000 5-gallon cuts per-gallon cost and reduces ordering frequency. Call us and we can confirm what your specific Castair rotary screw unit holds per oil change.
What's in the Box
- 1 gallon (128 fl. oz.) of Castair CAST-LUBE Full Synthetic Rotary Screw Compressor Oil
- Factory-sealed container
Technical Specifications
- Part Number: GA4000
- Volume: 1 gallon (128 fl. oz.)
- Oil Type: Full synthetic
- Application: Castair rotary screw compressors ONLY — not for piston compressors
- Service Interval: 1 year or 4,000 hours (whichever comes first)
- Approved By: Castair factory specification
Why Buy From Air Compressor Factory Direct?
We have been supplying Castair compressors and genuine Castair consumables since 2016. When it is time to change oil on your rotary screw unit, you want the factory-specified lubricant — not a generic compressor oil from a big-box store that may not meet the formulation requirements for rotary screw injection systems. We stock the full CAST-LUBE line, offer free shipping, and can advise on quantity per your unit's oil capacity. Free tech support is available at 866-217-0063.
Call 866-217-0063 for quick answers and help!
