Engine oil leaks are a common problem on small airplanes with piston engines. But how much oil leakage is too much? Here’s an indicator: If there’s oil on the nose tire, and it paints a stripe on the pavement with each revolution, that’s too much oil leakage.
This was the case the other day on a Cessna 172, so we did some detective work to see where the oil was coming from.
After removing the cowling, it was obvious the oil leak was significant, and it appeared to be coming from the left side of the engine.
Here’s what we discovered about the rocker oil return line on cylinder #4:
The wire that holds the engine baffles in place under cylinders 2 and 4, had cut a hole in the bottom of the rocker cover oil return line. When the engine is running, this line continuously returns oil from the rocker arm area back to the crankcase. With engine vibration, this is a common area for chafing to occur, and is an important area to inspect.
Here’s a closer look at the oil line after it was removed. The spiral wrap was a previous attempt to prevent chafing, but the wire still cut through the line.
After removing the spiral wrap, the chafed area was clear:
It doesn’t take a very large hole to make a big oil mess!
This story reminds me of some helpful principles for evaluating engine oil leaks:
If engine oil is dripping on the nosewheel, it’s probably not normal and needs to be checked.
If something changes, check it out. Example: engine breather tubes sometimes drip after shutdown, but if you notice a dramatic increase, make a further investigation.
When troubleshooting oil leaks, go to the highest point on the engine where you see oil. Oil can run down on lower components and lead to wrong conclusions about the source of the oil leak.
Verify all connections and fittings are tight.
Listen to the audio in today’s episode to hear about some other loose fittings that recently caused problems… one on a Piper Turbo Arrow, and one on a Piper Saratoga.
After a successful career in computers early in life, Carl Valeri decided years ago it was time to pursue his passion for aviation. Since that time, he’s been an airline pilot, flight instructor, aviation careers coach, mentor, Piper Cherokee pilot, and many other things.
Carl is well known as the host of two podcasts, the Aviation Careers Podcast, and the Stuck Mic AvCast. You can find him in both of those places:
In today’s episode, we talked about all kinds of fascinating things, including:
Carl’s background and how he got into aviation.
How he was hired years ago as an airline pilot, and furlowed the same year, in 2011.
How his struggle served to prepare him for what has become one of his greatest passions… “Helping people move forward with their aviation career.”
What the acronym “CAMEL” means to an airline pilot… I had never heard this before, and I thought it was really cool.
Carl’s current opportunity to lease and fly a Piper Cherokee… the 12th Cherokee to come off the line years ago.
The maintenance issues he’s encountered recently with the Cherokee.
And since this is the Airplane Owner Maintenance podcast, it’s only appropriate that we document this part with some pictures.
ISSUE #1: Smoke in the cockpit! Apparently somebody forgot to tighten an oil line!
The oil made a mess on the cowling. And upon closer examination, the source was identified – the rocker oil return line B-nut had come loose. When the oil dripped down on the hot exhaust, it produced smoke that made its way into the cockpit.
Solution and reminder: Always double check engine fluid lines and hoses, and apply torque putty to the B-nuts.
ISSUE #2: Fuel leak. Carl told us about a leak that showed up under the airplane on the left side. Listen to the episode to hear his advice about how to communicate with your A&P about issues like this.
It turned out the leak was from his “gascolator” or fuel strainer. Here are the parts from this ancient piece of technology… just like you might have seen on your grandpa’s tractor!
In this situation, Carl made the wise decision to upgrade to a “Steve’s Aircraft” gascolator, a much better design with increased reliability and ease of maintenance. Take a look:
ISSUE #3: Exhaust leak. Carl noticed some abnormal discoloration at the cowling seam.
It turned out there was a significant leak at one of the exhaust sleeve transitions in the engine compartment.
This situation is a little different than many Cherokees, since this particular engine was installed with an STC.
ISSUE #4: Electrical problem. With the benefit of 20/20 hindsight, Carl was able to recognize how the airplane had been showing some warning signs of this issue… be sure to listen to the audio to get the details.
What seemed like a complex problem in the beginning, turned out to be a blown fuse.
Sometimes the little things can make a big difference!
In spite of the maintenance challenges, Carl still loves to fly the Cherokee. I think one reason why is because he shares his love for aviation with others:
In telling about his aviation adventures in life, Carl is quick to acknowledge that, “I could never have done any of that without the help of others.” Now, he’s “paying it forward” in so many ways to help those who are coming behind him.
And finally, to finish up with a little humor: “Even an airline pilot who flies jets, recognizes there’s something missing in the following picture!
Carl, thank you very much for pushing all of us to keep moving forward and appropriately pursue our aviation dreams! We appreciate you, and I sure am glad flying still puts a smile on your face!
“There’s no RPM drop when I select left mag, and if I turn the ignition switch off, the engine continues to run.”
That’s what the owner of this Cirrus reported when he arrived at our airport the other day.
One of our technicians got to work to troubleshoot the problem. Here’s what he found:
The magneto P-lead wiring checked good.
The ignition switch checked good.
It appeared the problem was with the magneto.
So let’s pause and ask, “Which magneto, left or right?”
Good question, because this stuff can sometimes be confusing.
When the pilot got no RPM drop when selecting left mag, it likely means the ability to ground (or turn off) the right mag has been lost. So even though we are selecting left mag, it’s the right mag that actually has the problem.
And sure enough, that’s exactly the case here… upon removing the point cover from the right mag (which also contains a capacitor with a stud for the P-lead attachment,) we determined with an ohm meter check that the capacitor in the P-lead circuit had failed in the open position, making it impossible to ground (or turn off) the right magneto.
The point cover along with the capacitor, mounts to the magneto as seen on the left side of the following picture:
The new capacitor has been ordered and the Cirrus should be flying again real soon. You can hear the full story in today’s podcast episode.
The other P-lead story in this episode is from an A36 Bonanza I’m inspecting. This is a very different situation… this one had some chafing P-leads in the engine compartment that were a problem-in-the-making. Take a look:
After pulling the wires down a bit, the worn areas became really obvious:
These wires have 4 layers:
An inside center wire (the actual P-lead.)
A layer of insulation on the center wire.
A layer of braided shielding to prevent radio noise.
An outside layer of insulation.
Thankfully, the inside wires (P-leads) were still protected… if those inside wires had shorted to ground, the magnetos could have failed to operate. If the P-leads are shorted to ground by touching the airframe, it’s the same effect as turning the ignition switch off.
Here’s one last picture of the P-leads with some context of how they are attached to the magnetos:
So… any time you’re working in the engine compartment, whether for an oil change, or anything else, it’s a good idea to look around for any signs of chafing… sometimes you might be able to avoid a future in-flight problem by catching the issue early.
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