Running at high temperatures (above 100C at the element outlet) degrades the oil and reduces separator efficiency. The oil thins out, foams more, and breaks down faster -- all of which increase the amount of oil that passes through the separator into the compressed air.

What you'll see

Oil in the compressed air that coincides with high operating temperatures. The element outlet temperature is above 90-100C. The oil may appear darker than normal (heat degradation), and the separator element may need replacing sooner than expected because the degraded oil clogs it faster. It is a vicious cycle: heat degrades oil, degraded oil clogs separator, clogged separator creates more pressure drop, more pressure drop means more heat.
Before you assume this is the problem

Fix the overheating problem first. Oil carry-over from high temperature will resolve when temperatures return to normal. See: Clogged Radiator, Low Coolant or Oil, Fan Belt Failure.

See all causes of oil in compressed air →

How to diagnose

  1. Check element outlet temperature

    What is the temperature reading at the screw element outlet? Normal operating range is 70-95C depending on ambient conditions and design. Above 100C, oil starts to degrade faster. Above 110C, most machines will trigger a high-temperature shutdown. If the machine is running consistently at the high end of the range, oil carry-over increases.
    Result: Temperature above 95C = contributing to oil carry-over. Fix the cooling issue.

  2. Check oil condition

    Drain a small sample and inspect. Fresh compressor oil is clear/amber. Heat-degraded oil is dark brown or black. It may have a burnt smell. Degraded oil loses its anti-foaming properties and separates poorly. If the oil has degraded, it needs changing -- along with the separator element, which will have been contaminated by the degraded oil.
    Result: Dark/burnt oil = change oil and separator. Clean oil = temperature may not have caused damage yet.

How to fix it

  1. Fix the overheating cause

    Address whatever is causing the high temperature: clean coolers, fix fan/belt, check coolant, repair thermostatic valve, reduce load, or improve ventilation. See the Overheating problem page for all possible causes.

  2. Change oil and separator

    If the oil has darkened from heat, change both the compressor oil and the separator element. The degraded oil will have contaminated the separator. Running fresh oil through a contaminated separator shortens the new oil life. Replace both together for a clean start.

Common mistakes

Do not just keep changing oil and separator without fixing the underlying overheating problem. The new oil will degrade at the same rate as the old oil if the temperature is still too high. Fix the cooling issue first, then change oil and separator. Also: do not mix compressor oil types. Mixing synthetic and mineral oil can cause compatibility issues, foaming, and accelerated degradation.

Parts & tools

Replacement compressor oil. Replacement separator element. Tools for cooling system repair depending on the root cause.

Review safety precautions before starting →

Safety

High operating temperatures indicate a cooling or lubrication problem. Address the root cause to prevent compressor damage.

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