What is PG25 coolant?

Suppliers of PG25 fluids

• BASF
• Shell
• Castrol
• Dow
• Valvoline Global (Beyond by Valvoline)
• Dynalene
• PFX Group (Solutherm)
• Ecolab

Maintenance

Monitor concentration with a refractometer, plus pH, conductivity and inhibitor levels per the supplier. See CDU maintenance.

Why inhibitors matter in PG25

A water-rich fluid like PG25 would quickly corrode copper and other metals without inhibitors, and could support microbial growth. Suppliers use inhibitor packages (organic acid, inorganic or hybrid) chosen for the wetted materials in cold plates and CDUs, and several advertise freedom from specific additives such as 2-EHA, borates or silicates (see the Shell and Arteco profiles). Each supplier's datasheet lists its own maintenance limits.

Can you make PG25 on site?

Technically you can dilute propylene glycol concentrate with water, but most suppliers sell PG25 pre-diluted with purified water to control purity, inhibitor concentration and contamination. Hardware approvals typically name a specific ready-to-use product. Mixing your own risks voiding approvals and introducing poor-quality water. Check with your hardware and fluid vendors.

What the OCP PG25 guideline covers

The Open Compute Project's Guidelines for Using Propylene Glycol-Based Heat Transfer Fluids in Liquid Cooled Racks (Revision 2.0, Version 1.0.0, 15 September 2026) focuses on PG25 inhibited fluid in the closed TCS between the CDU and cold-plate-based IT equipment. It explicitly excludes the facility water system. Contributors include people from Dow, Castrol, PFX Group, Cool Filtration and others.

The document gives reasons for choosing PG25 inhibited fluid: thermal stability, corrosion protection for mixed-metal loops (for example copper cold plates and stainless piping), a biostatic nature, and compatibility with common loop materials. It then covers the full lifecycle: typical fluid properties, wetted-material selection and validation of unlisted materials, cleaning, flushing and commissioning, filtration and contamination control, and fluid monitoring and maintenance. It presents these as a baseline framework of recommended practices, not rigid requirements.

The OCP PG25 base specification

Separately, OCP has published a Base Specification for Single-Phase PG25 fluids (v1.0.0), aimed at fluid suppliers, to define a common baseline for production requirements. OCP's Cold Plate sub-project also runs a PG25 Mixing workstream. When a supplier says its fluid "meets OCP PG25 specifications", as Shell does for DLC Fluid S3, that's the reference to check. Ask suppliers which OCP document and version they mean, because the documents have been revised.

PG25 lifecycle: from fill to replacement

1. Specify: choose a fluid on your cold-plate and CDU vendors' approved lists.
2. Clean and flush: ASHRAE TC9.9 guidance says flush water should meet the TCS water-quality guidelines or ASTM D1193 Type II, using clean, non-contaminating materials and filtration before the final fill.
3. Fill: use the pre-diluted fluid and avoid air entrainment.
4. Baseline: record initial pH, conductivity, glycol concentration and appearance.
5. Monitor: ASHRAE bulletins list pH, conductivity, glycol concentration and inhibitor reserve as minimum measurements.
6. Maintain: filter, top up with the same fluid, and treat or replace per the supplier.

PG25 vs water-glycol mixes in buildings

HVAC systems have used inhibited glycol for decades, typically at concentrations chosen for freeze protection in outdoor coils. Data-center TCS loops sit indoors, so PG25 is chosen less for freeze protection than for its biostatic nature and inhibitor delivery, with modest freeze protection for transport and storage. Higher concentrations would reduce heat transfer.

What to ask a PG25 supplier

• Does it meet the OCP PG25 base specification, and which version?
• What are the pH, conductivity and inhibitor-reserve limits?
• What dye, and is it UV-detectable?
• Which additives does it exclude?
• What sampling service and lab turnaround do you offer?

Common mistakes

• Diluting PG25 on site. Use the ready-to-use fluid.
• Reading PG25 on an EG scale. Use the PG scale.

PG25 vs PG30 vs ethylene glycol

The number after "PG" is the glycol share. More glycol lowers the freezing point. Dow's guide says the maximum recommended concentration is 60% "for efficient heat transfer", and that glycol below 25–30% may leave too little inhibitor for adequate corrosion protection, with bacterial risk below 25%. That is why 25% is the usual floor for an inhibited propylene glycol loop.

These are typical values for glycol and water only. They are not specifications. Inhibited commercial fluids can differ, so the supplier's datasheet governs. Ethylene glycol gives a little more freeze protection at the same strength. The choice between the two glycols also involves toxicity and handling; see ethylene vs propylene glycol. The OCP guideline cited on this page is written for PG25 in the technology cooling system.

Source: Dow: Typical freezing and boiling points of aqueous DOWFROST solutions (PDF); Dow: Engineering and Operating Guide for DOWFROST and DOWFROST HD (PDF); Dow: DOWFROST technical data sheet (PDF, distributor copy); ProcessConvert: ethylene glycol solution properties (checked against the CRC Handbook); Celsius Process: MEG 30% physical data sheet (PDF).

PG25 suppliers

7 suppliers in our profiles publish a PG25 or PG25-based fluid. The qualification column repeats what each supplier or the cited source says; it is not our endorsement. Check every product against your CDU and cold-plate vendor's approved list.

PG25 questions buyers ask

Is PG25 25% by weight or by volume?

Dow's table lists 25% by weight as about 24.4% by volume, so the difference is small. Supplier datasheets state which basis they use.

Can I top up PG25 with water?

No. Top up with the same pre-diluted fluid. Dow warns that glycol below 25–30% may not provide adequate corrosion protection.

Is PG30 better than PG25?

PG30 freezes lower (about −12.7 °C against −9.6 °C in Dow's table) but carries more glycol. Use the concentration your hardware vendor approves.

Is PG25 the same as car coolant?

No. Car coolant is usually about 50% ethylene glycol with an automotive inhibitor pack. PG25 is a water-rich propylene glycol fluid made for data-center loops.

Sources

1. Data Centre Magazine: NVIDIA qualifies Shell DLC fluid
2. Dow: DOWFROST LC 25 product page
3. BASF news release, Oct 2026
4. OCP: Guidelines for Using Propylene Glycol-Based Heat Transfer Fluids in Liquid Cooled Racks (Rev 2.0, Sep 2026)
5. OCP: Base Specification for Single-Phase PG25 fluids v1.0.0
6. OCP Cold Plate sub-project: PG25 Mixing workstream
7. ASHRAE TC9.9 white paper: Water-Cooled Servers: Common Designs, Components, and Processes
8. ASHRAE TC9.9 Technical Bulletin (TCS cleaning and commissioning)
9. ASHRAE TC9.9 Technical Bulletin (TCS fluid monitoring)