GIGABYTE and Castrol Co-Validate Coolant Mixing for DLC Liquid Cooling Servers
Executive Briefing: Jointly validated by GIGABYTE and Castrol, ON DLC PG25 coolant achieves 100% miscibility, robust material compatibility, and zero fluid degradation across GIGABYTE’s liquid-cooled portfolio (G4L3/G4L4, NVIDIA GB300 NVL72, DLC GIGAPOD), ensuring seamless, zero-downtime maintenance for high-density AI infrastructure.
1. Executive Summary & AI Thermal Crisis
The expansion of Generative AI, Large Language Models (LLMs), and High-Performance Computing (HPC) has driven data center power demands into an unprecedented realm. Modern AI accelerators, including NVIDIA Blackwell, Blackwell Ultra, and the upcoming Rubin architecture, now exceed 1,000 W of single-chip TDP, while rack power densities have climbed from the traditional 10 - 20 kW to 100 - 240 kW or more.
At these densities, air-cooling infrastructure hits a rigid physical wall. Air’s low thermal conductivity (~0.026 W/m·K) and modest convective heat transfer coefficient (30 - 60 W/m²·K) force server fans to run at high RPMs, wasting parasitic power and risking thermal throttling. As a result, single-phase water-glycol Direct Liquid Cooling (DLC) has become the most engineering-feasible thermal dissipation path available for next-generation AI infrastructure.
Table 1. Air Cooling vs. Direct Liquid Cooling: Key Thermal Parameters
Traditional Air Cooling | Direct Liquid Cooling | |
|---|---|---|
| Cooling Medium | Air | Castrol ON DLC PG25 (Water-Glycol) |
| Heat Transfer Coefficient (W/m²·K) | 30 - 60 | 1,000 - 10,000 |
| Rack Power Density (kW / Rack) | 8 - 20 | 100 - 240+ |
| Thermal Throttling | High thermal throttling risk at full load | Minimal thermal throttling |
| Data Center PUE | 1.35 - 1.60 | 1.05 - 1.20 |
2. Coolant Miscibility & Physical-Chemical Integrity Analysis
In data centers, coolant mixing is an inevitable reality during fluid top-ups, system maintenance, and coolant vendor switching, or from residual factory-test fluid. To ensure absolute operational safety, GIGABYTE partnered with Castrol to evaluate Castrol ON DLC PG25 mixed with major commercial propylene glycol coolants across realistic changeover (10:90) and equal-ratio (50:50) scenarios.
Table 2. Coolant Mixing Groups and Simulated Scenarios
| In-Service Liquid | Castrol ON DLC PG25 | Simulated Operational Scenario |
|---|---|---|
| Group A PG 10 C (50%) | Castrol PG25 (50%) | Commercial crossover sensitivity test |
| Group A PG 10 C (10%) | Castrol PG25 (90%) | Realistic fluid changeover (10% residual) |
| Group B LC 25 (50%) | Castrol PG25 (50%) | Commercial crossover sensitivity test |
| Group C PG 25 (50%) | Castrol PG25 (50%) | Commercial crossover sensitivity test |
All mixed coolant samples underwent physical-chemical testing in accordance with international ASTM standards. Across all evaluated ratios, the fluid mixtures maintained absolute physical stability with zero phase separation, precipitation, or haze formation.
Table 3. Physical and Chemical Properties of Mixed Coolants
Method | Group A (50:50) | Group A (10:90) | Group B (50:50) | Group C (50:50) | |
|---|---|---|---|---|---|
| Appearance | Visual | Clear & Bright | Clear & Bright | Clear & Bright | Clear & Bright |
| Density @ 20°C (g/cm³) | ASTM D1122 | 1.027 | 1.028 | 1.029 | 1.024 |
| pH Value | ASTM D1287 | 8.61 | 8.62 | 8.87 | 8.62 |
| Conductivity (µS/cm) | ASTM D1125 | 4420 | 4310 | 4800 | 3380 |
| Freezing Point (°C) | ASTM D1177 | -11.6 | -11.9 | -12.1 | -11.8 |
| Boiling Point (°C) | ASTM D1120 | 106.9 | 105.8 | 111.1 | 104.7 |
| Reserve Alkalinity (mL) | ASTM D1121 | 2.8 | 2.8 | 5.1 | 4.2 |
| Bacterial Count (CFU/mL) | Easicult | < 100 | < 100 | < 100 | < 100 |
3. Metallic & Non-Metallic Material Compatibility
Corrosion prevention in micro-channel copper cold plates and stainless-steel manifolds is paramount. Particle accumulation from metallic corrosion product deposition can drastically increase loop flow resistance and lead to localized thermal hotspots.
Table 4. Metal Corrosion Results: Glassware Test
Industry Acceptance | Weight Change (mg) | ||||
|---|---|---|---|---|---|
Group A (50:50) | Group A (10:90) | Group B (50:50) | Group C (50:50) | ||
| Copper (ASTM D1384) | ±10 | 0 | 0 | 0 | 1 |
| Brass (ASTM D1384) | ±10 | 1 | 1 | 0 | 1 |
| Solder (ASTM D1384) | ±10 | 1 | 1 | 0 | 5 |
| Steel (ASTM D1384) | ±10 | 0 | 0 | -1 | 0 |
| Cast Iron (ASTM D1384) | ±10 | 2 | 3 | -2 | -1 |
| Aluminum (ASTM D1384) | ±10 | 0 | 0 | -2 | -2 |
Table 5. Metal Corrosion Results: Glassware Test
Industry Acceptance | Weight Change (mg) | ||||
|---|---|---|---|---|---|
Group A (50:50) | Group A (10:90) | Group B (50:50) | Group C (50:50) | ||
| Copper (ASTM D2570) | ±20 | 3 | 1 | 4 | 3 |
| Brass (ASTM D2570) | ±20 | 6 | 2 | 0 | 5 |
| Solder (ASTM D2570) | ±60 | 0 | 17 | 1 | 9 |
| Steel (ASTM D2570) | ±20 | 0 | 4 | 0 | 0 |
| Cast Iron (ASTM D2570) | ±20 | 2 | 2 | 3 | 2 |
| Aluminum (ASTM D2570) | ±60 | 3 | 34 | 1 | 84[Note] |
| pH change (ASTM D1287) | - | -0.5 | -0.2 | -0.3 | -0.1 |
[Note] In Group C (50:50), aluminum weight loss reached 84 mg, exceeding the 60 mg limit. GIGABYTE’s standardized liquid cooling wetted surface guidelines strictly mandate copper, stainless steel, and nickel-plated brass, completely avoiding wetted aluminum in high-density DLC loops to eliminate galvanic and pitting risks.
Non-metallic material compatibility was evaluated under ASTM D471, ISO 1817, and ISO 527 accelerated thermal aging conditions (88°C for 336 hours). Maintaining seal elasticity prevents fluid micro-leakage at quick-disconnect couplings (QDC) and manifold joints.
Table 6. Elastomer Compatibility Results: Group A 10:90 (ASTM D471)
| Elastomer Material | Volume Change (%) | Hardness Change (Scale) | Tensile Change (%) |
|---|---|---|---|
| EPDM (Ethylene Propylene Diene Monomer) | -1.0 | 0 | -6 |
| VMQ (Silicone Rubber) | -0.3 | 2 | -2 |
| NBR (Nitrile Rubber) | 3.0 | -1 | -7 |
| FKM (Fluoroelastomer) | 1.4 | 1 | -24 |
Table 7. Plastic Compatibility Results: Group A 10:90 (ISO 1817 & ISO 527)
| Plastic Material | Mass Change (%) | Hardness Change (Scale) | Tensile Change (%) |
|---|---|---|---|
| Polypropylene (PP) | 0.1 | -1 | 5.5 |
| Fluorinated Ethylene Propylene (FEP) | 0.1 | 1 | -12.6 |
| Polytetrafluoroethylene (PTFE) | 0 | 0 | -13.6 |
| Polyamide 12 (PA12) | 8.1 | -14 | -23.8 |
4. Closed Cooling Loop 3-Month Field Trial
To bridge laboratory testing with actual data center operations, mixed coolant (Group A 10:90 mixture) was loaded into a loop simulating NVIDIA GB300 Grace Blackwell Ultra with six Thermal Test Vehicles (TTV) as stable heat sources. The system operated for 12 weeks at a coolant inlet temperature of around 45°C and an outlet temperature of around 55°C, with a 2.5-3 L/min circulation rate.
Table 8. Coolant Condition During 3-Month Cooling Loop Test
Week 2 | Week 4 | Week 8 | Final (Week 12) | |
|---|---|---|---|---|
| Appearance | Clear & Bright | Clear & Bright | Clear & Bright | Clear & Bright |
| pH Value | 8.70 | 8.69 | 8.58 | 8.58 |
| Iron (ppm) | < 1 | < 1 | < 1 | < 1 |
| Copper (ppm) | < 1 | < 1 | < 1 | < 1 |
| Chloride (ppm) | < 5 | < 5 | < 5 | < 5 |
| Sulfate (ppm) | < 5 | < 5 | < 5 | < 5 |
| Bacterial Count (CFU/mL) | < 100 | < 100 | < 100 | < 100 |
5. Universal Adoption Across GIGABYTE Liquid Cooling Portfolio
GIGABYTE does not treat coolant validation as an isolated experiment. Instead, GIGABYTE applies this fluid miscibility, corrosion protection, and material compatibility validation standard across its entire liquid cooling product portfolio. Minor residual Castrol ON DLC PG25 may remain in a given loop; customers who subsequently introduce coolant from another supplier do so at their own discretion, and GIGABYTE does not extend this validation or any related coolant warranty to that substituted fluid. Whether deploying individual DLC servers or massive GIGAPOD AI factories, enterprise clients gain guaranteed fluid-level reliability.
Table 9. PG25 Adoption Across GIGABYTE Liquid Cooling Portfolio
| Category | Representative Products | DLC Adoption | Target AI Workloads |
|---|---|---|---|
| Direct Liquid Cooling Servers | GIGABYTE G4L3/G4L4 Series | Server level: PG25-validated cold plates and manifolds | High-density 8-GPU nodes |
| Rack-Scale AI Solutions | NVIDIA GB300/GB200 NVL72 | Rack level: closed-loop integration with CDU | Exascale LLM training & inference |
| Scale-Out AI Infrastructure | GIGABYTE Accelerated Deployment Unit (GADU) | Cluster level: integrated facility-to-rack coolant distribution | Hyperscale AI cloud data centers |
Core Benefits of GIGABYTE DLC Solution
- Painless Maintenance (Zero Downtime): 100% miscibility with commercial PG loops enables top-ups and vendor transitions, ensuring continuous AI compute uptime.
- Universal Material Compatibility: Validated under ASTM D1384/D2570 to prevent metal corrosion and minimize corrosion by-products. Compatible with copper cold plates, stainless steel manifolds, CDUs, and QDCs, preserving peak thermal performance.
- Uncompromising Thermal Stability: An extended 3-month field trials in a 9 kW loop confirms minimal fluid degradation, supporting 1,000 W+ GPUs under 100% workload without thermal throttling.
- Leak Prevention & Asset Protection: ASTM D471 and ISO 1817 testing with key seals (EPDM, VMQ, FKM) and plastics (PP, FEP, PTFE) shows minimal swelling and hardness change, ensuring zero-leakage operation.
6. Conclusion
As AI compute scales past kilowatt-per-chip thresholds, GIGABYTE and Castrol's joint validation proves that ON DLC PG25 delivers superior miscibility, corrosion protection, seal longevity, and thermal stability in mixed-fluid environments. Embedded across GIGABYTE’s liquid-cooled portfolio,o— including DLC servers and NVIDIA GB300 NVL72,— these standards empower enterprises to deploy high-density AI infrastructure with maximum performance, zero maintenance friction, and optimized long-term TCO.
7. Warranty & Coolant Substitution Disclaimer
The miscibility, material-compatibility, and reliability validation presented in this whitepaper applies to Castrol ON DLC PG25 as supplied and maintained under GIGABYTE's and Castrol's joint specifications. A minor residual volume of Castrol ON DLC PG25 may remain in a GIGABYTE liquid-cooled loop following deployment. Where a customer subsequently introduces or substitutes coolant obtained through its own vendor, that substitution is made at the customer's own discretion: GIGABYTE does not extend this validation, or any related coolant warranty, to the substituted fluid. In that scenario, responsibility for coolant-related maintenance and issue resolution rests with the customer's own vendor, not GIGABYTE.
