When the compressor runs too hot, the oil gets thin and passes right through the separator. Fix the overheating first -- the oil problem usually goes away with it.

What you'll see

Oil carry-over combined with high temperature readings. The discharge temperature is above 100 degrees C (212 degrees F), possibly hitting 110+ degrees C (230 degrees F). The oil looks thinner than normal, might be dark or have a burnt smell. The compressor may be tripping on high temperature as well.
Before you assume this is the problem

If the discharge temperature is normal (80-90 degrees C / 175-195 degrees F) and you still have oil carry-over, temperature is not your problem. Look at the separator, scavenge line, oil level, or MPV instead.

Could also be:

See all causes of oil carry-over →

How to diagnose

  1. Check the discharge temperature

    The controller should display discharge or element outlet temperature. Normal is around 80-90 degrees C (175-195 degrees F). Above 100 degrees C you'll start seeing increased oil carry-over. At 110+ degrees C the oil becomes very thin and oil carry-over increases dramatically. This creates a vicious circle: oil gets carried out, oil level drops, less oil means less cooling, which means even higher temperatures.
    Result: Temp above 100 degrees C + oil in air = overheating is the root cause.

How to fix it

  1. Fix the overheating first

    This page is about oil in air, but the actual fix is to solve the overheating. Check ventilation, cooler cleanliness, oil level, thermostatic valve, and maintenance items. See the dedicated overheating cause pages for detailed diagnosis and fixes. Once the temperature comes down to normal operating range, oil carry-over usually stops on its own.

  2. Top up oil if needed

    After running hot with excessive carry-over, the oil level may have dropped below minimum. Top up to the correct level. But fix the temperature problem first -- adding oil to a compressor that's still overheating just gives it more oil to blow into the air lines.

Common mistakes

Don't replace the separator element thinking it's the separator's fault when the real problem is overheating. A new separator will have the same oil carry-over if the temperature is still 110+ degrees C. Also: low oil level caused by carry-over makes overheating worse, which causes more carry-over. Break the cycle by fixing the temperature problem, then topping up oil.

Parts & tools

No parts specific to oil carry-over -- the parts you need are for the overheating fix (thermostat, cooler, oil, filters). See: Overheating cause pages.

Review safety precautions before starting →

Safety

Everything in and around the compressor is extremely hot when running at these temperatures. Let it cool before touching anything.