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Product knowledge · Specialty fluid

Thermic / Heat Transfer Fluid

Heat-transfer fluid assessed for thermal cracking, oxidation, viscosity, flash point, acidity and low-boiler formation.

Reviewed Jul 2026 · Oil Testing Atlas editorial team
Definition and scope

What this product reference covers.

Thermic fluid transfers heat in a closed or open system and may be mineral, synthetic aromatic, silicone or other approved chemistry.

Types and grades

Products within the family.

Names used in commerce can overlap. Use the nominated standard and exact grade rather than relying on a generic product label.

01

Mineral heat-transfer oil

Mineral heat-transfer oil is a recognised thermic / heat transfer fluid category whose exact composition, grade limits and suitability must be confirmed from the governing specification and equipment requirement.

02

Synthetic aromatic fluid

Synthetic aromatic fluid is a recognised thermic / heat transfer fluid category whose exact composition, grade limits and suitability must be confirmed from the governing specification and equipment requirement rather than inferred from the generic label.

03

Silicone heat-transfer fluid

Silicone heat-transfer fluid is a recognised thermic / heat transfer fluid category whose exact composition, grade limits and suitability must be confirmed from the governing specification and equipment requirement rather than inferred from the generic label.

04

Food-grade heat-transfer fluid

Food-grade heat-transfer fluid is a recognised thermic / heat transfer fluid category whose exact composition, grade limits and suitability must be confirmed from the governing specification and equipment requirement rather than inferred from the generic label.

Formulation architecture

What the product is built from.

Thermic / Heat Transfer Fluid formulation overview
ComponentTechnical role
Mineral, synthetic or renewable base fluidProvides the principal lubricating film and viscosity-temperature foundation.
Anti-wear / extreme-pressure systemProtects loaded contacts where the application requires it.
Antioxidant and corrosion inhibitorsControl ageing, deposits and surface corrosion.
Application-specific additivesTune detergency, friction, demulsibility, air release, tackiness or seal compatibility.
Purpose of testing

Define the decision before selecting the panel.

  1. 01

    Confirm new thermic / heat transfer fluid identity, grade and fitness for the intended application.

  2. 02

    Detect contamination, degradation, mixing or storage-related change.

  3. 03

    Investigate abnormal equipment, combustion, filtration or handling behaviour.

  4. 04

    Establish a representative baseline for later comparison.

  5. 05

    Support specification, maintenance and root-cause decisions with corroborated evidence.

Tests, methods and interpretation

What each result contributes.

“High” and “low” are directional investigation prompts, not pass/fail decisions. Corroborate them using the correct specification, baseline and companion evidence.

Thermic / Heat Transfer Fluid test significance and directional causes
Test / parameterTypical methodsWhy it mattersPossible causes when highPossible causes when low
Kinematic viscosityASTM D445 / ISO 3104Confirms grade and detects dilution, shear, oxidation or mixing.Oxidation, wrong oil, soot, evaporation or heavy contamination.Shear, fuel/solvent dilution, wrong grade or lighter make-up oil.
Acid numberASTM D664Trends acidic constituents, oxidation and contamination against a new-oil baseline.Oxidation, overheating, acidic contamination or wrong fluid.Fresh oil, make-up dilution or formulation difference.
WaterASTM D6304Quantifies moisture relevant to corrosion, additive loss and film strength.Condensation, cooler/seal leak, washdown, storage or sampling contamination.Dry operation or dehydration; hot sampling can reduce free-water representation.
Elemental analysisASTM D5185 with PQ / ferrography where neededScreens wear, contaminants and additive chemistry within method limitations.Wear, corrosion, dirt, additive source, wrong oil or maintenance debris.Stable wear, dilution, filtration or particles too large for ICP response.
FTIR conditionASTM E2412 trendingTracks oxidation and selected molecular contaminants against a comparable reference.Heat, extended service, contamination or depleted antioxidant reserve.Fresh oil, make-up dilution or a non-comparable baseline.
Perspective 02

Condition-monitoring application.

Once the product is in service, the question changes from “does it meet a product requirement?” to “what has changed, why, how confident are we and what action is proportionate?”

  1. 01Use a stable, representative sampling point and document operating hours, top-ups, transfers and maintenance.
  2. 02Trend method-consistent results rather than treating one value as a complete diagnosis.
  3. 03Separate new-product conformance from in-service condition and machine-wear questions.
  4. 04Escalate correlated evidence and rate of change; confirm surprising results before major action.
Connected test references

Open the method-level detail.

Browse the complete test library →
Official orientation sources

Verify the current edition.

ISO 6743-99 — Classification of lubricants, industrial oils and related productsOfficial source ↗