Question:
With an airplane piston engine, how much oil leakage is too much?

Answer: “It is difficult to achieve zero oil leakage on many aircraft piston engines. That makes it easy to become complacent, especially if your airplane has been leaking a small bit of oil for a long time. However, as in all areas of aviation, complacency is dangerous. Here are some indicators that might indicate a bigger problem:

If it’s dripping on the nose tire in a single-engine airplane. Engines sometimes leak a little oil out the breather tube after shutdown, but the tube outlet is usually away from the nose tire. If oil leaks on the nose tire, it is likely a significant leak that runs down the inside of the bottom cowling, making its way to the center aft area. This is an indicator that something is wrong.

If you can’t take a 4-hour trip with your airplane without worrying about the oil level. You have enough things to be thinking about in flight, without wasting mental energy on wondering if you will run out of oil in the engine.

If your oil consumption exceeds the manufacturer’s recommendation. Do some research for maximum oil consumption for your specific engine, and if it’s more than the recommended amount, it’s worth evaluating the situation.

Finally, if the line guy says, ‘That’s a lot of oil under your engine, we need to get that cleaned up,’ you have a problem. A big enough puddle on the ramp to attract attention probably needs a visit to the maintenance shop before your next flight.”

Tip Courtesy of PilotWorkshops

Brian’s Last Words

When we got the engine overhauled on the 195 in 2012 the oil consumption was about a gallon every 6-8 hours. After the overhaul I expected to see it drop to less than a gallon every 15-20 hours. The engine was broken in correctly but the consumption never was better than a gallon every 8 hours.

The common saying with radial engines is “if they’re not leaking oil it means there is none”. Our engine never leaked oil – half a paper towel was enough to clean up some minor spots. In the next 450 hours oil consumption started to slowly increase until 2022 when we were burning a gallon every 2 hours. I definitely didn’t like a 4 hour flight any more so it was time to do some further investigation.

The Jacobs engine manual says that once the oil consumption is more than 1 gallon per hour then you might consider there could be a problem. Well, we hadn’t reached that consumption level yet but the engine was definitely talking to me. As you are aware when we pulled the cylinders off one set of rings on #5 were in pieces.

Our aircraft will let us know something is not quite right but you have to listen and understand what it is telling you. There may be subtle hints but if you are aware of normal operations you’ll hear them. Just don’t ignore them.