Quick answer: SUNISO 3GS is the lighter mineral oil grade at 30 cSt at 40 °C, while SUNISO 4GS is the heavier grade at 55 cSt. The manufacturer’s application table lists both for several piston applications, but screw-compressor rows select 4GS at -25 °C and -35 °C, then 3GS at -50 °C. The compressor model, refrigerant and evaporating temperature should be checked together before a repair order.
A cold-room repair starts with the oil already in the compressor. The service record, compressor nameplate and refrigerant identify the operating context. The replacement grade then has to match the equipment documentation and the temperature range shown in the service data.
The oil circuit lubricates bearings and travels through the separator and return line. Viscosity and low-temperature behaviour affect how the charge moves through the system. A grade change belongs in the repair record with the compressor model, refrigerant, operating temperature and quantity.
| Property | SUNISO 3GS | SUNISO 4GS | Reference basis |
|---|---|---|---|
| ISO viscosity grade | 32 | 56 | Current PCL product records |
| Viscosity at 40 °C | 30 cSt | 55 cSt | Current PCL product records; ASTM D445 method |
| Viscosity at 100 °C | 4.4 cSt | 5.9 cSt | Current PCL product records; ASTM D445 method |
| Density at 15 °C | 0.910 kg/L | 0.916 kg/L | Current PCL product records; ASTM D4052 method |
| Flash point | 178 °C | 184 °C | Current PCL product records; ASTM D92 method |
| Pour point | -48 °C | -42 °C | Current PCL product records; ASTM D97 method |
| Floc point | -58 °C | -54 °C | Product reference data |
| Dielectric strength | 37 kV | 40 kV | Product reference data |
The main difference is the viscosity class. 4GS carries a higher viscosity at both reference temperatures. 3GS is the lower-viscosity grade, with the lower pour point in the current product data. The compressor documentation and the order data should use one consistent grade reference.
The SUNISO GS/GSD application table uses refrigerant, evaporating temperature and compressor type together. For R22 at -25 °C, the piston column lists 3GS and 4GS, while the screw column lists 4GS and 5GS. At -35 °C, piston again lists 3GS and 4GS, and screw lists 4GS. At -50 °C, the table lists 3GS for piston and screw duty.
For R290 at -30 °C, the piston row lists 3GS, 4GS and 5GS. For R717 at -30 °C, piston lists 3GS and 4GS while screw lists 4GS. At -50 °C, the R717 row lists 3GS for piston and screw.
These rows put the choice in context. The heavier grade is not the answer for every cold-room repair. The table changes with the compressor type and evaporating temperature.
4GS appears in the screw-compressor column for R22 at -25 °C and -35 °C, and for R717 at -30 °C. The product record identifies it as a highly refined mineral refrigeration lubricant with 55 cSt at 40 °C and 5.9 cSt at 100 °C.
A screw-compressor quote should include the exact model, refrigerant, evaporating temperature, oil separator arrangement and the grade named in the equipment documentation. For equipment under warranty, follow the equipment builder’s recommendation. When changing oil technology or brand, flush the system to reduce contamination with the previous charge. The published 4GS service case follows this model-first process for an industrial screw-compressor service order.
3GS is the lower-viscosity option in this pair. The published application table places it in piston duty for R22 at -25 °C, -35 °C and -50 °C, and in screw duty for R22 and R717 at -50 °C. It is also listed in the R290 piston row at -30 °C.
The 3GS product page records 30 cSt at 40 °C, 4.4 cSt at 100 °C, a -48 °C pour point and a -58 °C floc point. Those values help the buyer screen a low-temperature request, while the compressor documentation decides the order.
Send the compressor brand and model, refrigerant, evaporating temperature, existing oil grade, required quantity, pack size, destination country and destination port. A photo of the nameplate and the current container label shortens the technical check.
For a single cold-room repair, the 4 L product photographs show the pack format available for both grades. Distributor orders can be quoted against the required pack plan, payment term and delivery term. Qishanr supplies the original PCL SUNISO products and can also assess a replacement-grade route when the compressor details and current oil are provided.
Qishanr supplies the PCL SUNISO 3GS and 4GS products. The 4GS product page carries the grade data, pack information and supply terms. The 4GS service case also records model verification, production updates, sealed drums and export documents as part of an industrial order.
For a replacement request, send the equipment details and the current oil label. The response can then match the available PCL SUNISO grade to the repair requirement and quote the pack arrangement.
Only when the compressor documentation and operating conditions allow the heavier grade. 3GS and 4GS differ in viscosity, so they should not be treated as interchangeable labels during a repair.
The manufacturer application table lists 4GS in the screw-compressor column for R22 at -35 °C. The compressor model and service documentation still belong in the order check.
The R717 row at -50 °C lists 3GS in the screw-compressor column. The same table lists 4GS for R717 screw duty at -30 °C.
Send the compressor model, refrigerant, evaporating temperature, current oil grade, required quantity, pack size and destination. A nameplate or product-label photograph makes the check faster.
© 2026 Guangzhou Qishanr Technologies Co., Ltd. This article, SUNISO 3GS vs 4GS: Choosing Mineral Refrigeration Oil for a Cold-Room Compressor Repair, was first published on October 21, 2026 at https://qishanrlubricants.com/blog-detail/suniso-3gs-vs-4gs-cold-room-compressor-repair.
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