Oil leak

[isaacpr7]

My 68C has developed an oil leak since the last MX worked on the engine. I had him look at it and he tightened a few bolts on the oil pan and called it good. Next morning, the oil continues to seep over night and I cannot find where it is coming from because it looks wet everywhere (mostly from the back side); however, the oil seems to be seeping from a point higher than the oil pan in the back side. Has anyone experienced this before?

[orionflt]

I. Had one that hid from me for a yr, I narrowed it down to the prop control area but could not isolate it. Finally I pulled the prop control and found it was coming from a seal under the spring. It was in a location that was only identified when we tested it on the bench.

[jrwilson]

What about case seam? That would drain back down to lowest point

[DaV8or]

I think it's just a fact of life that these engines leak oil after a short while. The environment and temperature extremes are just too great to stay oil tight forever. Therefore, chasing oil leaks requires a strategy.

1. Does the leak look to be an indication of a safety hazard?
2. Does the oil actually make it to the floor of the hangar?
3. How much is it going to cost to fix this crappy little, annoying leak?

Except that the engine will have leaks. Calculate your annoyance threshold. Proceed within the limits of your operating budget and time. Mine leaks oil. I know exactly where the leaks are. The plane is in no danger of engine failure. The oil never makes it to the floor. I can live with it until either annual in the case of some in the past, or in the case of a rebuild in the case of one I have. The amount of oil I leak never registers on the dip stick.

[isaacpr7]

I think it's just a fact of life that these engines leak oil after a short while. The environment and temperature extremes are just too great to stay oil tight forever. Therefore, chasing oil leaks requires a strategy.

1. Does the leak look to be an indication of a safety hazard?
2. Does the oil actually make it to the floor of the hangar?
3. How much is it going to cost to fix this crappy little, annoying leak?

Except that the engine will have leaks. Calculate your annoyance threshold. Proceed within the limits of your operating budget and time. Mine leaks oil. I know exactly where the leaks are. The plane is in no danger of engine failure. The oil never makes it to the floor. I can live with it until either annual in the case of some in the past, or in the case of a rebuild in the case of one I have. The amount of oil I leak never registers on the dip stick.

Dave,

 

My concern is that the oil leak reaches all the way to the ground. I comes from somewhere in the upper rear portion of the engine and makes its way through the lower cowling into the tire and floor.  I have noticed that the leak eventually stops after the oil level reads 6 quarts on the dip stick. 6 quarts is the minimum my POH allows for flight and my concern is that it will get even lower while in flight.

[Rwsavory]

Your engine will run just fine on a lot less than 6 quarts, regardless of what your poh says.

[flyingvee201]

Check around your fuel pump gasket and the pump case itself. Mine had a hairline crack on the pump case. I had the engine washed and couldnt find it right away. I taxied it back to my hangar and came back a week later, opened the cowling and started looking again.....sure enough....after putting my hand underneath the pump,my hand was wet with oil. MX showed me the tiny crack in the aluminum case.

Replaced it and no more leaks.

(Also replaced the rocker cover gaskets with newer style red silcone type)

[Bob - S50]

Dave,

 

My concern is that the oil leak reaches all the way to the ground. I comes from somewhere in the upper rear portion of the engine and makes its way through the lower cowling into the tire and floor.  I have noticed that the leak eventually stops after the oil level reads 6 quarts on the dip stick. 6 quarts is the minimum my POH allows for flight and my concern is that it will get even lower while in flight.

Our J has an 8 qt capacity but we quickly determined it spits everything over 6 quarts overboard.  We now fill it to 6 quarts and keep it between 5 and 6.

 

Another place you might check for an oil leak.  When we did some extensive work on our plane last summer, we found an oil leak where the vacuum pump mates to the accessory drive case.  Apparently one or the other was not exactly flat so a small leak developed.  We ended up using a slightly thicker gasket material than normal and solved the problem.

[cliffy]

Chasing leaks can be a PIA. Wash the engine and go run it for 5 mins then look for the oil trail. If you can't see any oil. cowl it up and fly it around the pattern and then check. Eventually you will find the leak. You say 6 qts and it stops? MY first thought is the engine breather line. Where does it exit from the cowl? Right near where the breather tube exits? Also I'd check real close on the rocker drain line connections. Sometimes they are hard to see.

[N601RX]

I had a very hard to find oil leak to find on the back of the engine. It turned out to around the vac pump shaft seal. It was getting on the spinning shaft and getting slung to other spots. It was getting slung clear of the pump and did not appear to be leaking from the pump.

There are also 2 types of vac pump gaskets. One style has a hole in it to supply oil to the old style wet pumps. Tempest makes a gasket that does not have the hole in it and is less prone to leak.

[Hank]

Dave,

 

My concern is that the oil leak reaches all the way to the ground. I comes from somewhere in the upper rear portion of the engine and makes its way through the lower cowling into the tire and floor.  I have noticed that the leak eventually stops after the oil level reads 6 quarts on the dip stick. 6 quarts is the minimum my POH allows for flight and my concern is that it will get even lower while in flight.

What year is your C? My Owners Manual from 1970 doesn't have that line. At change, I put in 7 quarts, and don't add any until it drops to 5-1/2. For long trips, I will add some only to reach 6 on the dipstick.

The accessory drive is a common leak, so is the breather tube. But if you're trying to hold it at 7-8 quarts, I'd not consider it a leak. Check your belly, too--it should stay cleaner at 6 quarts.

Good luck either way! Let us know what you find.

[isaacpr7]

Check around your fuel pump gasket and the pump case itself. Mine had a hairline crack on the pump case. I had the engine washed and couldnt find it right away. I taxied it back to my hangar and came back a week later, opened the cowling and started looking again.....sure enough....after putting my hand underneath the pump,my hand was wet with oil. MX showed me the tiny crack in the aluminum case.

Replaced it and no more leaks.

(Also replaced the rocker cover gaskets with newer style red silcone type)

As I was finishing up replacing the spark plugs today, I noticed that the fuel line that goes into the carburetor was very wet. My first thought was that there was a fuel leak in the line. I chased the line up to the pump and noticed that the bottom of the pump was nasty and very wet with oil. I think it might be seeping out of the gasket as you suggested. The bad thing is, reaching that pump is just as easy as working on a Pontiac Fiero, LOL! There is no room for my hands at all.

[isaacpr7]

What year is your C? My Owners Manual from 1970 doesn't have that line. At change, I put in 7 quarts, and don't add any until it drops to 5-1/2. For long trips, I will add some only to reach 6 on the dipstick.

The accessory drive is a common leak, so is the breather tube. But if you're trying to hold it at 7-8 quarts, I'd not consider it a leak. Check your belly, too--it should stay cleaner at 6 quarts.

Good luck either way! Let us know what you find.

It is a 68C. I think I finally found the culprit. I suspect it is the seal at the bottom of the fuel pump because it is the highest point I was able to identify with oil all over it.

[jnisley]

Make sure the oil line fitting that goes to the prop governor is tight, on my M20F the fitting can be visually inspected with the passenger side panel off.

[kmyfm20s]

Just replaced a fuel pump that was causing an oil leak as well.

[isaacpr7]

Just replaced a fuel pump that was causing an oil leak as well.

Did you have to replace the entire fuel pump or just the gasket? If you replaced the pump, how much did it set you back?

[kmyfm20s]

Yes, I replaced the entire pump. My fuel pressure was starting to fluctuate and I also noticed the oil. I ordered it from Aircraft Spruce $398 and the Gasket $1.85. I don't know how many hours he charged me but it was a real PIA so I'm guessing 6. He ended up taking out the Magneto to get to it.

[N201MKTurbo]

I have had the prop governor (H1) leak a substantial amount of oil from the internal seal at the oil pump. It will only leak when the engine is running.

If you pull the left mag the fuel pump is pretty easy to get to.

[mike_elliott]

Chasing leaks can be a PIA. Wash the engine and go run it for 5 mins then look for the oil trail. If you can't see any oil. cowl it up and fly it around the pattern and then check. Eventually you will find the leak. You say 6 qts and it stops? MY first thought is the engine breather line. Where does it exit from the cowl? Right near where the breather tube exits? Also I'd check real close on the rocker drain line connections. Sometimes they are hard to see.

 

The rocker drain lines can develop a small hole on them if they are in contact with anything and as Cliffy says, be a real PIA to find. One thing I would do different than what Cliffy suggests, is after you completely clean the engine, let it dry then get some magnaflux developer (or absent that, some white athlete's foot spray powder) and spray everything white that you suspect a leak from. Then fire that sucker up and run it hard for about 5 minutes...you will find your leak...You might not like it, but you will find it. (check around #2 cylinder for cracks also...lord forbid)

[fantom]

If a Lycoming isn't oozing a bit of oil somewhere, there's none in the engine.

[Piloto]

My 68C has developed an oil leak since the last MX worked on the engine. I had him look at it and he tightened a few bolts on the oil pan and called it good. Next morning, the oil continues to seep over night and I cannot find where it is coming from because it looks wet everywhere (mostly from the back side); however, the oil seems to be seeping from a point higher than the oil pan in the back side. Has anyone experienced this before?

I had a similar leak type. It would only leak overnite when filled above 7qts. Since it only leaks overnite the only possible source is the oil sump. I cleaned and dried the sump to check for leaks next day. I filled to 8 qts. Sure enough the leak was a pinhole on the sump at the 7qts level. The pinhole was must likely created during the casting process of the sump. It was located in a grainy area of the case. I drained the oil below the pinhole cleaned it very well with MEK and then applied Marine Tex over the pinhole area. Problem solved. It is not unusual for a casting to have certain degree of porosity.

 

José

[kmyfm20s]

Always check any through bolts for leaks also. I replaced one of mine with a +.001 over and stopped an oil leak. The oil leaks between the cylinders hit the baffling shield and can blown to the back of the engine.

[Andy95W]

Does anyone know the final outcome of this leak? Did it turn out to be the fuel pump gasket for sure? Just curious...

[isaacpr7]

Does anyone know the final outcome of this leak? Did it turn out to be the fuel pump gasket for sure? Just curious...

N1395W,

I have not had a chance to work on it because my MX has been out of town but he is supposed to come back tomorrow. I have to have him check my mags and the oil leak while at it. I will post the update here for eveyone to know the veredict

[isaacpr7]

Does anyone know the final outcome of this leak? Did it turn out to be the fuel pump gasket for sure? Just curious...

So I finally get my MX to come over to my hangar to check out some of the critters lurking inside the engine compartment. I was able to use a handy dandy inspection camera I bought at harbor freight and inspected all those hard to reach places arund the accessory gear box. I was relieved to see that the seam around the fuel pump, vacuum pump, and both magnetos were pretty clean; however, as I was looking at the fuel pump I noticed that the oil pan seam just below the fuel pump was completely saturated oil build up.  My MX also pointed out a second leak located in the spinner seal to the engine. The leak on the oil pan is a stronger and seems to leak on engine shutdown and the one on the spinner seems to mist oil very lightly during operation.