A low heater-outlet temperature, noisy pump, slow warm-up or uneven automotive-part heating does not prove that the heat-transfer fluid has failed. By following the pressure, flow, temperature and sampling checks in sequence, you can separate circulation faults, commissioning mistakes, mechanical failures and fluid degradation before changing grade or draining the system.
Key takeaways
- Record pressure, flow and temperature at the same operating condition.
- Check bypasses, strainers, pump rotation and trapped air before increasing heater duty.
- Send a representative fluid sample for viscosity, acidity and contamination testing.
- Verify the approved grade, batch identity and supply documents before filling.
Start with pressure, flow and temperature readings—not the oil
A low heater-outlet temperature does not prove a circulation fault. Insufficient pump flow, an open bypass, air or vapour, a blocked strainer, wrong pump rotation, or a failed sensor can all produce it. Record pressure, flow and temperature together; differential pressure across the heater and user equipment is more diagnostic than temperature alone.
Take readings in this order:
- Pump suction and discharge pressure, then calculate pump differential pressure.
- Differential pressure across the strainer; a rising value indicates restriction.
- Flow indication at the pump or main circuit, checked against the design flow.
- Heater outlet and return temperatures at the same load.
- Expansion-tank level and pressure, including signs of vapour or gas release.
| Reading pattern | Likely indication | Immediate check |
|---|---|---|
| Low suction pressure with noisy or fluctuating discharge | Cavitation, low expansion-tank level, blocked suction line or excessive inlet restriction | Check tank level, suction valve, strainer and pipework |
| Normal pump pressure but low measured flow | Closed valve, stuck bypass, blocked strainer or incorrect rotation | Confirm valve positions, strainer differential pressure and motor rotation |
| High heater outlet temperature with low return temperature | Inadequate circulation, fouled heater surface or failed control valve | Verify actual flow, heater duty and sensor calibration |
| Uneven user-equipment temperatures | Air lock, restricted branch or poor balancing | Vent only through the designed high point and inspect branch restrictions |
Do not raise heater duty until these measurements are reconciled. That can overheat stagnant fluid while the heat transfer fluid circulation issues remain unresolved.
Match each symptom to the likely restriction, air or equipment fault
Low flow is a circuit clue, not proof that the fluid has failed. Compare pump suction and discharge pressure, flow indication, strainer differential pressure, heater differential pressure and expansion-tank level before changing oil.
- Low flow with high pressure drop across the strainer indicates a blocked strainer; high drop across the heater or user equipment indicates fouling, a closed valve or a restricted pipe. Low flow with little pump pressure points to incorrect rotation, a damaged impeller, an open bypass or inadequate expansion-tank level.
- Cavitation sounds like gravel and makes discharge pressure fluctuate. Check suction pressure, hot oil at the pump inlet, the suction line, strainer and expansion-tank connection. Bengaluru’s lower atmospheric pressure reduces NPSH margin by roughly 1 metre of liquid head, exposing marginal pump designs sooner.
- Air locking gives intermittent flow, rattling, sudden temperature swings and cold sections. Look for trapped high points, incomplete venting, low expansion-tank level and leaks on the suction side.
- Pressure changes that follow valve movement identify control or bypass faults; pressure changes that pulse with pump speed indicate vapour, air or mechanical damage.
- Uneven heating reveals poor distribution, a partially closed branch valve, blocked passage, air pocket or fouling on a heater surface. A faulty temperature sensor can imitate the same problem if its probe sits in a stagnant pocket.
These heat-transfer-fluid circulation issues require a circuit inspection before increasing heater duty. Raising duty against restricted flow can overheat the film, accelerate deposits and trigger repeated trips.
Correct commissioning and operating conditions before raising heater duty
Before increasing heater duty, restore circulation and confirm that the temperature readings represent the process. Extra heat can overheat the heater film when flow is restricted, causing low-flow trips, oil cracking and deposit formation.
1. Check pump suction pressure, discharge pressure and flow indication. Compare the pressure drop across the strainer and main user with the commissioning record; a rising drop points to blockage, while low differential pressure can indicate cavitation, wrong pump rotation or a bypass stuck open.
2. Confirm every valve position, including the heater bypass, user bypass and expansion-tank isolation valves. Check the expansion-tank level and vent trapped air only through the designed high point; do not loosen fittings on a hot circuit.
3. Compare heater outlet and return temperatures with the actual flow. A high outlet temperature with low flow indicates restricted circulation or excessive heater input. A low return temperature can result from an open bypass, air or vapour, a blocked strainer or poor flow through the user.
4. Verify the temperature sensor against a calibrated instrument and inspect its location. A sensor in a stagnant pocket can report a false high or low value.
5. Check burner input or electrical heater duty, control-valve movement and heater differential pressure. Inspect for fouling if heat-up remains slow after flow is restored.
If water is suspected, isolate the heater and circulate at controlled low temperature only under the equipment procedure. Vent vapour safely, then confirm dryness by laboratory testing. Never raise duty to overcome repeated trips.
Prove fluid degradation with a representative sample
A darkened oil or cracking odour is evidence worth testing, not proof that the oil caused a high-temperature alarm. Confirm actual circulation and heater performance before changing oil; a mechanical defect can produce the same symptom.
Take the sample from the circulating line while the system operates within its safe sampling procedure. Flush the sample valve and dead volume, use a clean, dry, labelled container, and record oil temperature, sampling location, date, batch number and top-up history. Do not sample from a non-circulating pocket.
Send a sealed sample of unused oil from the same batch as the comparison baseline.
Request these laboratory tests:
- Kinematic viscosity at 40 °C and 100 °C, compared with the unused-fluid result.
- Acid number, reported in mg KOH/g, to show oxidation and acidic breakdown.
- Flash point, using the same test method as the baseline where possible.
- Water by Karl Fischer or an equivalent named method.
- Insolubles or sediment, with a visual colour and deposit description.
- Distillation or gas chromatography for low-boiling fractions, where available.
A large viscosity or acid-number rise, lower flash point, water, sediment or increased light fractions supports fluid degradation. A normal report alongside abnormal pressure or flow readings points to circulation or mechanical trouble. Clear oil does not clear it: chemical damage can precede visible sludge.
Choose the approved grade and protect its identity through supply
Do not choose HYTHERM 600 because its number sounds “higher.” Compare the current technical data sheets for bulk-temperature limit, maximum film temperature, viscosity at your coldest start-up, flash point, compatibility and drain/refill procedure. A high-temperature alarm still demands flow, heater-duty and sensor checks before changing grade.
| Grade | Compare before approval | Selection decision |
|---|---|---|
| HYTHERM 500 | Bulk and film limits, start-up viscosity, flash point and compatibility | Approve only when every value suits the circuit |
| HYTHERM 600 | The same data, not a presumed higher temperature rating | Approve only when its data sheet matches the duty |
| Either grade | Mixing risk, refill procedure and additive compatibility | Do not blend or top up with unrelated mineral oil |
For “hytherm 500 600 in bengaluru,” specify the exact approved grade, not “thermal oil” or “machinery oil.” The phrase “general purpose machinery oil wholesalers hp” identifies a buying route, not an interchangeable fluid; using circulating, gear, hydraulic or bearing oil can create general purpose machinery oil wholesalers hp heat transfer problems in bengaluru.
Require this from your heat transfer oil supply:
- Sealed original containers, batch number and certificate or technical data sheet
- Delivery-date control and a retained sample from every batch
- Clean, dedicated transfer hoses; reject reused or wet equipment
- Covered storage away from rain and damaged drums
- A defined emergency quantity for an unplanned drain
Bangalore Industrial Oils can be assessed against these controls rather than judged by product availability alone. Water in a drum or hose can flash at the heater, cause hammering and accelerate degradation. Verify dryness by laboratory testing before commissioning.
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Frequently asked questions
Which readings help diagnose heat transfer fluid circulation issues?
Record pump pressure, flow, heater-inlet temperature and heater-outlet temperature together. Compare differential pressure across the heater and user equipment to identify restrictions or circulation faults.
What causes a low heater-outlet temperature?
Insufficient pump flow, an open bypass, trapped air or vapour, a blocked strainer, wrong pump rotation and a failed temperature sensor can all cause a low reading.
Should you increase heater duty when the outlet temperature is low?
First correct commissioning and operating conditions. Check flow, bypass position, air removal, strainer condition, pump rotation and sensor operation before raising heater duty.
How do you confirm heat transfer fluid degradation?
Take a representative sample from the circulating system and test it for properties such as viscosity, acidity and contamination. Do not judge degradation from colour alone.
How do you protect the identity of an approved heat transfer fluid?
Confirm the specified grade, retain the product name and batch number, inspect seals and packaging, and keep the delivery documents with the system records. For grades such as Hytherm 500 or Hytherm 600, verify the exact approved specification before filling.
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