As AI, high-performance computing and cloud workloads drive rack power densities ever higher, traditional air cooling is reaching its limits. To meet today’s thermal demands, data centres are increasingly turning to Immersion Liquid Cooling — and at the heart of this technology is a new generation of specialist dielectric fluids. This is where Castrol ON DC 20 come in.

A purpose-engineered data centre cooling fluid designed specifically for single-phase immersion cooling of electronic and electrical systems. Combining excellent thermal efficiency, outstanding dielectric protection and broad material compatibility, it enables operators to cool next-generation infrastructure safely, efficiently and at scale.

Why Immersion Liquid Cooling Is Transforming Data Centre Cooling

With CPUs and GPUs now exceeding traditional thermal envelopes, airflow alone is no longer sufficient. Modern processors generate heat faster than air can remove it.

Immersion Liquid Cooling solves this by fully submerging IT hardware in a non-conductive dielectric fluid. Heat transfers directly into the liquid, which is then circulated through a heat exchanger.

This approach delivers:

• Significantly higher heat removal efficiency

• Support for ultra-high rack densities

• Reduced cooling energy consumption

• Lower fan power and noise

• Improved hardware reliability and lifespan

But the performance of immersion cooling depends entirely on the quality of the fluid — and that’s where Castrol ON DC 20 excels.

Introducing Castrol ON DC 20 Immersion Cooling Fluid

Castrol ON DC 20 is a synthetic hydrocarbon-based dielectric coolant developed specifically for single-phase immersion cooling of electrical and electronic systems.

It delivers:

• Excellent flow properties

• High thermal performance

• Superior oxidative and hydrolytic stability

• Excellent dielectric protection

• Outstanding low-temperature performance

These characteristics make it an ideal data centre cooling fluid for hyperscale, AI, edge and HPC environments.

Key Advantages of Castrol ON DC 20

Optimised for Immersion Liquid Cooling

Castrol ON DC 20 is a low-viscosity fluid, allowing it to circulate easily through immersion tanks and heat exchangers. This enables rapid heat removal from high-power processors.

Excellent Thermal Performance

With strong thermal conductivity and high specific heat capacity, Castrol ON DC 20 efficiently absorbs and transports heat away from submerged IT equipment.

Outstanding Dielectric Protection

As a fully dielectric coolant, Castrol ON DC 20 provides:

• Very low electrical conductivity (<35 pS/m)

• High dielectric strength (>14 kV/mm)

• High dielectric breakdown voltage (>35 kV)

This allows electronic components to operate safely while fully submerged.

Long Fluid Life and Stability

Castrol ON DC 20 delivers:

• Excellent oxidative stability

• Strong hydrolytic stability

• High flash and fire points

• Ultra-low pour point for cold-start environments

This ensures long service life even in demanding operating conditions.

Typical Performance Characteristics

From Castrol’s Product Data Sheet, Castrol ON DC 20 delivers the following typical properties:

• Viscosity @ 40°C: 5.1 mm²/s

• Density @ 15.6°C: 797 kg/m³

• Pour Point: -57°C

• Thermal Conductivity @ 40°C: 0.135 W/mK

• Specific Heat Capacity @ 40°C: 2.2 kJ/kgK

• Electrical Conductivity @ 25°C: <35 pS/m

• Dielectric Constant: 2.06

• Flash Point: 169°C

• Fire Point: 191°C

• Appearance: Clear & bright

These properties make Castrol ON DC 20 highly effective for continuous, high-density immersion cooling operation.

Material Compatibility for Immersion Cooling Systems

Material compatibility is critical in immersion cooling systems. All elastomers, plastics and metals used in submerged environments must be compatible with the cooling fluid.

Castrol ON DC 20 has been tested across a wide range of commonly used materials and demonstrates excellent compatibility under normal operating conditions.

Materials with Good Compatibility

Castrol ON DC 20 shows good compatibility with:

Elastomers

• Acrylic Rubber (ACM)

• Fluorocarbon Rubber (FKM)

• Hydrogenated Nitrile Rubber (HNBR)

• Ethylene-propylene diene monomer (EPDM)

• Polyurethane Rubber (PUR)

• Fluorosilicone Rubber (FVMQ)

• Liquid Silicone Rubber (LSR)

Metals

• Aluminium

• Copper

• Steel

• Nickel

• Nickel-plated steel

Plastics

• Polycarbonate (PC)

• Polyoxymethylene (POM)

• Polytetrafluoroethylene (PTFE)

• Polyamide (PA6, PA12, PA46, PA66)

• Polyphthalamide (PPA)

• Polyphenylene Sulfide (PPS)

• Polyimide (PI)

Materials Requiring Evaluation

Some materials show moderate or poor compatibility depending on grade and manufacturer, including:

• Silicone rubber (VMQ)

• Chloroprene rubber (CR)

• Polyvinyl chloride (PVC)

• Certain nylons and elastomer blends

Castrol recommends testing the exact grade of material before deployment.

Designed for Modern Data Centre Cooling Infrastructure

Castrol ON DC 20 is designed for use in:

• Single-phase immersion cooling tanks

• Electrical and electronic cooling systems

• AI and HPC data centres

• Edge computing facilities

• Hyperscale data centres

It enables operators to deploy high-density compute with lower cooling energy, reduced infrastructure footprint and improved sustainability.

Why Data Centres Choose Castrol ON DC 20

Data centre operators select Castrol ON DC 20 because it delivers:

• Proven immersion cooling performance

• Excellent dielectric safety

• High thermal efficiency

• Long operational life

• Broad material compatibility

• Backing from Castrol’s global technical support network

It is engineered specifically for the demands of modern Immersion Liquid Cooling and next-generation Data Centre Cooling Fluid applications.

Final Thoughts: Powering the Future of Immersion Liquid Cooling

As the data centre industry moves toward higher rack densities and lower carbon footprints, immersion cooling is rapidly becoming the new standard.

Castrol ON DC 20 provides the performance, protection and reliability required to support this shift — delivering safe, efficient and scalable cooling for the world’s most demanding digital infrastructure.

For operators planning the next generation of immersion-cooled data centres, Castrol ON DC 20 offers a proven and future-ready cooling foundation.

Need Technical Support?

For compatibility testing, deployment guidance or technical documentation, contact your Kernow Oils representative or visit:

info@kernow-oils.co.uk