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The oil system performs many different functions:

  • Lubricates the engines moving parts.

  • Helps cool the internal parts of the engine.

  • Removes heat from the cylinders.

  • Carries away contaminates.

There are two types of oil systems for reciprocating engines, wet-sump or a dry-sump:

  • A wet-sump design is when the oil is located an integral part of the engine. Wet-sump system use oil pumps to draw oil from a sump and sends it to the engine.

  • A dry-sump system is where the oil is located in an external or separate oil tank from the engine. Oil pumps are also used and recycles the oil, by pumping it from the tank to the engine and is return back to the oil tank.

The oil pressure gauge is indicated in pounds per square inch (PSI). The normal operating range is in the green are.

Whereas the oil temperature gauge measures the temperature of oil. A green area shows the normal operating range, and the red line indicates the maximum allowable temperature. Unlike oil pressure, changes in oil temperature occur more slowly.

Keep in mind that these two gauge a designed different in different airplanes.

It is best to always periodically check the oil temperature during flight especially when operating in high or low ambient air temperature. If there is a high oil temperature indication, this may signal:

  • A plugged oil lines.

  • Low oil quantity

  • Blocked oil cooler

  • Defective temperature gauge.

Low oil temperature indications may signal improper oil viscosity during cold weather operations.

Always refer to the AFM/POH or any placards for proper oil type, weight, and the proper maximum and minimum oil quantity.

Always check the oil level by using the dipstick during the preflight operation. If the oil level is indicating low on the dipstick, simply add oil.


Always make sure the airplane is parked on a level surface, to get an accurate oil dipstick indication.

When flying on hot summer days or on long cross-country flights always bring a couple extra bottles of oil.

Real World Scenario:

This actually happen one morning just before Thanksgiving, I was getting ready for a flight to Camarillo, California that morning from the Riverside airport (KRAL), in Riverside, CA. When I checked the oil level on the deep stick, the oil level showed 5 quarts. On this particular airplane, a PA-28 Piper Arrow, the max oil level for the engine oil system is 6 quarts, and the lowest oil level is 3 quarts.

After I had crossed the Pomona VOR, I had looked down to do a quick check of all the engine indications and noticed that the oil pressure gauge needle was in the yellow arc near the red line (not a good sign). I then looked at the oil temperature gauge and saw it was reading a hotter temperature than normal.

I immediately contacted SoCal Approach and told them I was cancelling my flight to the Camarillo airport and needed to return to Riverside airport. SoCal, then cleared me back to Riverside and asked what the issue was. I had informed them, "I have low oil pressure indicated, with no other issues at this time." SoCal approach then asked me, "Are you declaring an emergency at this time...


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