By Qishanr Technical Team · Published 21 September 2026
Retrofit report · QISHANR 5GS · Bitzer CSH screw compressor, ISO VG 100 mineral oil
QISHANR 5GS is a naphthenic mineral refrigeration oil in the ISO VG 100 grade, the heaviest grade in the QISHANR GS series. It is built for large screw and reciprocating compressors where the OEM nameplate calls for a 100 cSt mineral oil.
| Customer | An industrial refrigeration maintenance team (not named) |
| Application | Bitzer CSH series screw compressor running on ISO VG 100 mineral oil |
| Product | Qishanr 5GS — ISO VG 100 naphthenic mineral refrigeration oil, 100 cSt at 40 °C |
| Before the change | Knocking at cold start, growing noise under load, and an oil pressure gauge that fluctuated as the system loaded and unloaded |
| After the change | Quiet cold starts, noticeably lower vibration, no abnormal noise at 90 % load, steady oil pressure, fast pressure build on cold mornings |
| Energy | About 8 % lower average consumption across two months of kWh meter readings |
| Documents | SGS report and MSDS supplied with the shipment; can sealed on arrival |
| Grade match | Meets the OEM ISO VG 100 specification (Bitzer B5.2 cross-reference) |
The unit had been running on degraded oil. The team drained it, refilled with QISHANR 5GS and reported back once the machine was back in service. Their message is quoted in full:
We replaced the degraded oil in our Bitzer CSH screw compressor with QISHANR 5GS. Before, the compressor knocked at cold start and got noisy under load. After the change, cold starts are quiet, vibration dropped noticeably, and even at 90% load there's no abnormal noise. The oil pressure gauge is steady — no more fluctuation when the system loads or unloads, and pressure builds quickly on cold mornings. We tracked our kWh meter for two months: average consumption dropped about 8%, mostly because the unit reaches setpoint faster and runs fewer hours. The oil matches the OEM ISO 100 spec (Bitzer B5.2), came with SGS report and MSDS, and the can was sealed properly.
The grade is set by the bearings. A large screw compressor carries rotor shafts above 80 mm in diameter on hydrodynamic bearings, where the oil film alone keeps the journals off the shells. Film thickness scales with viscosity.
An ISO viscosity grade describes an oil's kinematic viscosity at 40 °C, measured in centistokes. QISHANR 5GS sits at 100 cSt at 40 °C and 8.4 mm²/s at 100 °C.
Kinematic viscosity in this class is determined under ASTM D445, the method that measures resistance to flow at a controlled temperature.
Mineral oil is still the specified lubricant for a large part of the installed base running R22 and R717. A naphthenic base with low wax content keeps that oil mobile at the evaporator, where the oil and refrigerant mix, and keeps it returning clean through long suction lines.
5GS holds wax content below 0.5 %, so the oil does not flocculate in the refrigerant mixture at evaporator temperatures as low as −40 °C. That is what keeps oil returning through piping runs beyond 50 m.
Its pour point of −30 °C is measured by ASTM D97, the standard pour point test, and its 190 °C flash point by ASTM D92 in the Cleveland open cup.
The rule that follows is the OEM's, not ours: match the grade on the nameplate. Going up a grade adds film strength and drag together, so a VG 56 machine should stay on VG 56 and a VG 100 machine should stay on VG 100.
Both symptoms point at the oil supply rather than at the motor or the controls. Cold-start knocking is the metallic noise a compressor makes when the oil film has not yet formed between the bearing surfaces.
On a screw machine that noise appears in the first seconds after start-up, before the pump has pushed oil through the galleries and the film is carrying load.
The unit in this case knocked every cold morning and grew noisy as load came on. After the change, cold starts are quiet, vibration is noticeably lower and the machine runs without abnormal noise at 90 % load, which is where a screw compressor loads its rotor bearings hardest.
The gauge tells the second half of the story. A screw compressor varies its oil demand as the slide valve moves, and a thin or aerated oil lets supply pressure wander with it.
A gauge that swings on every load and unload step reports that instability. This one holds steady through the cycle.
Fast pressure build on a cold morning is a pumpability result. With a −30 °C pour point and a low-wax naphthenic base, the oil is still fluid when the plant is cold, so the pump pulls it and pressure arrives quickly instead of labouring through a gelled charge.
Three readings are worth logging after an oil change: the pressure differential across the filter, the sump oil temperature, and the appearance of oil returning to the separator.
A quiet cold start plus a steady gauge is what those readings look like when the film is working properly.
The team's own explanation is the one to start from: the unit reaches setpoint faster and therefore runs fewer hours. That is a statement about how long the compressor has to work for the same cooling, and the oil is one of the things that decides it.
A degraded or wrong-grade oil costs energy through internal leakage. A thinner film lets refrigerant and oil pass the rotor clearances and the slide valve more freely, so part of the swept volume never reaches the discharge line.
Volumetric efficiency falls and the compressor runs longer to move the same heat. Restoring a proper 100 cSt film tightens that leakage path again.
The second cost is drag, and it runs the other way. A heavier oil shears harder in the bearings and takes more power at the same speed, which is why grade selection is a match to the OEM figure rather than a case for going up a step.
What the team did next is what makes the number usable: they read the plant kWh meter for two months, compared the average against the period before the change, and saw about 8 % lower consumption.
Run hours, the load-unload ratio and the kWh meter over comparable ambient conditions are the three records a plant needs to repeat that check.
The values below are the published 5GS figures, shown with the test method behind each one.
| Parameter | Value | Method |
|---|---|---|
| Oil type / grade | Naphthenic mineral oil (MO), ISO VG 100 | ISO 3448 |
| Kinematic viscosity @ 40 °C | 100 cSt | GB/T 265 |
| Kinematic viscosity @ 100 °C | 8.4 mm²/s | GB/T 265 |
| Density @ 20 °C | 918 kg/m³ | GB/T 1884 |
| Flash point (COC) | 190 °C | GB/T 3536 |
| Pour point | −30 °C | GB/T 3535 |
| Wax content | Below 0.5 % | Manufacturer specification |
| Dielectric strength | Above 25 kV / 2.5 mm | Manufacturer specification |
| Batch viscosity tolerance | ± 3 % | Manufacturer QC |
| Cross-references | Bitzer B5.2, Suniso 5GS/5GSD, York/Frick E, McQuay F, Fusheng FS100M | Product cross-reference list |
| Grade matched on this job | OEM ISO VG 100 (Bitzer B5.2) | Customer's report |
Grade selection inside one oil family is a trade-off rather than a ranking, and that trade-off is what the chart below shows: film strength rises with viscosity while the cold-flow margin narrows with it.
Fig. 1 — The GS mineral series by grade: 3GS at 29 cSt, 4GS at 56 cSt and 5GS at 100 cSt at 40 °C, with pour points of −40 °C, −35 °C and −30 °C. The shaded band marks the ISO VG 100 requirement of the screw compressor in this case.
A: 5GS is an ISO VG 100 naphthenic mineral oil, cross-referenced to Bitzer B5.2 alongside Suniso 5GS/5GSD, York/Frick E, McQuay F and Fusheng FS100M. Check the oil designation on the nameplate or in the unit manual, then confirm the sump charge and pack size.
A: All three are naphthenic mineral oils from the same series, separated by viscosity: 3GS at 29 cSt, 4GS at 56 cSt and 5GS at 100 cSt at 40 °C. The higher grade carries more film strength for large bearing clearances and gives up cold-flow margin.
A: A degraded film lets refrigerant and oil slip past the rotor clearances and the slide valve, so volumetric efficiency drops and the compressor runs longer for the same cooling. Restoring a 100 cSt film tightens that path, so run time is the first thing to move.
A: Shipments go out SGS certified with an MSDS, a certificate of origin and a transport identification report for the sea leg, and the batch viscosity tolerance is held at ± 3 %. Cans are sealed before packing.
A: 5GS is cross-referenced as a direct replacement for a mineral-oil charge of the same grade, so a drain and refill covers the standard case: drain the old charge, replace the filter drier, refill to the sight glass, then run and recheck the level.
Moving from a different oil family, such as a POE or PAG system, is a separate decision — confirm it with us before the change.
Running a screw compressor on ISO VG 100 mineral oil? Send the compressor model, sump capacity and refrigerant — we confirm the grade, the batch documents and the lead time before you order. Request a 5GS Quotation
