A student pilot I know mentioned that every time he would preflight the training aircraft, he would find it low on oil. He went on to complain that it would take away from his scheduled flight time because he would have to chase down 2 quarts of oil to top off the Lycoming engine before each flight.
His mention of “2 quarts of oil” triggered me to ask him what the dipstick would read prior to him topping off the Lycoming engine. He replied that he always found the plane with only 6 quarts of oil and he would fill to 8 quarts.
Alarm bells went off in my head and I slipped into education mode.
I mentioned that according to Lycoming’s Technical Support Rep Brandon Dildine, the four-cylinder Lycomings can operate safely with as little as 2 quarts of oil. However, and this is a big “however,” a typical Lycoming four-cylinder engine usually stabilizes its oil consumption at 5 1/2 to 6 quarts. A six-cylinder engine with a 12-quart oil capacity typically stabilizes at between 9 and 10 quarts.
Mr. Dildine said to add the amount of oil required to complete the planned flight. Thus, if you were going to fly over hostile terrain for 12 hours, you might want to add more oil than you normally fly with. If you are going to go for a local flight where you know the engine won’t consume a significant amount of oil during the flight, leaving the oil level at 6 quarts should be fine.
Of course, these oil consumption and quantity requirements are based on a healthy engine with “average” oil consumption.
When adding oil, it is important to track how much is added and when. This will help you identify if the oil consumption increases, indicating a possible issue with the engine.
If your engine is mounted in a taildragger, the dipstick should be calibrated for the engine being mounted at an angle when on the ground. If you fly a homebuilt, you should verify the calibration of your dipstick.
In addition to discussing oil levels, Lycoming’s Mr. Dildine provided these tips:
When changing your oil do the following:
- Change the oil only after warming up the oil either through flight or by using a sump heater.
- Fill the filter with oil to saturate the paper filter. To avoid making a mess when installing the filter, it is OK to pour excess oil out of the filter into the sump.
- Every oil change, the suction screen should be removed, inspected, cleaned, and reinstalled with a new copper crush gasket. The suction screen can get clogged by carbon.
- Make sure any funnel you use to put oil in your engine is clean.
- When checking your oil level with fresh/clean oil, be aware the level may be difficult to see.
- Do not over-torque or tighten the dipstick.
- Make sure there is an O-ring on the dipstick.
Read these two service bulletins:
- Oil and Filter Change Recommendations
- Oil Servicing, Metallic Solids Identification After Oil Servicing, and Associated Corrective Action
Great article! A helpful reminder to fill to the oil quantity needed for the flight.
Nowhere have I ever seen guidance on whether the dipstick markings are with the stick fully seated or ‘dipped’ to the top of the threads. The difference can be almost a quart.
Good point, Mark. I’ve always assumed it was with the dipstick fully seated. That way you get the most consistent results. My engine (IO360) seems happiest at 6.5 quarts, so I generally top off oil in half-quart quantities. Another thing I have discovered is that if you check the oil level on a trip, always wait at least 15 minutes after shutdown to let the oil drain back to the sump. Otherwise, you end up adding more than you need.
From Lycoming:
The oil level gauge should be fully threaded into the tube to accurately measure the oil level..
Although most of the four-cylinder Lycomings can operate safely with as little as 2 quarts of oil, some (such as the IO-360-M1B) have a 4 quart minimum oil amount per Lycoming.
Great article, I have always written on the oil door of my airplanes what the max oil should be.
It’s worth explaining why the oil level drops so quickly when it is filled to max capacity and where that oil goes. When filled to max capacity the oil level inside the engine is higher, more oil gets splashed around by the moving parts and excess oil blows out the crankcase breather vent. A lot of it ends up on the belly of the airplane, the rest is spewed into the atmosphere.
So, more good reasons to fill the oil to operating requirements, not max capacity.
That is not always the case. If the engine installation includes an oil-air separator that returns the oil to the crank case, your oil level may remain fairly high. Either way, the engine is designed to run at full capacity and doing so will not harm it.
Interesting – I’ve seen these in cars but not in airplanes. I found this writeup informative: https://www.danhorton.net/Articles/Separator-or-Condenser.pdf
I have had a Sonex and a Onex both with Jabiru 3300 engines. The Onex could not be filled to oil level specified maximum. Doing so would result in the oil foaming and running very high oil temperatures. This was particularly true during the summer in N. CA. I didn’t seem to have the problem with the 3300 installation in the Sonex so I assumed it had something to do with the oil cooler installation. In the Onex a SCAT tube carried cooling air to the oil cooler and in the Sonex air was ducted directly to the oil cooler.