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My brand new Thunderbolt has an oil leak :-(

Amazon-1

Active Member
It is a brand new, Lycoming YIO-390-EXP33 purchased from Van's. It starts and runs great, but somewhere near the #1 cylinder (right front) I have a small oil leak. I don't see the obvious source, but it has a small puddle of oil on the engine case in front of the baffle, specks of oil on the back of the baffle and a small amount of oil drips on the engine case.

My first thought was that it was the cylinder hold down bolts, but my mechanic buddy checked the torque of all eight bolts and they were fine. I sort of think it could be one of the valve pushrod tubes though I don't see oil specifically there.

Lycoming tech support (Tyler) says it is covered under warranty, but I still need to figure out how to get it fixed. My mechanic says pulling the cylinder is about 5 hours of work minimum so I don't want to go there unless I have checked everything else.

Lycoming also suggested the crankshaft seal may be an issue but we checked that and it was OK.

I considered the propeller (Whirlwind 74HRT) but if that were the case the oil should be on both sides of the engine. If it were the prop governor it would be on the left side rather than the right.

Any comments, suggestions appreciated.

thanks,
 
Oil leak

Airflow does mysterious things around the front of the engine. I chase hard to find leaks but completely cleaning the engine, spraying on some dye penetratnt developer (powder) on suspect areas and running the engine long enough for it to dispense some oil. If no results with a little ground running you need to go fly. Try 10 minutes, if nothing 10 more. Keep it up till you see something. Finding the source at first indication of a leak is the ticket. I would do a lot of looking before pulling a cylinder.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
Sounds to me like the cylinder base "O" ring is leaking, it may have been twisted during installation.
 
I chase hard to find leaks but completely cleaning the engine, spraying on some dye penetratnt developer (powder) on suspect areas and running the engine long enough for it to dispense some oil.
For a cheaper alternative, use foot powder after cleaning the engine. You can get it in a pressurized can and spray it on like paint, the propellant evaporates leaving a white powder layer that makes it very easy to see any oil. Washes off afterwards with the same water and cleaner you used to clean the engine in the first place.
 
Pushrod tube seals is a good guess. I had a freshly rebuilt engine that leaked oil from half the pushrod tubes. They were never seated properly and the seals at the base leaked. As noted, the air flow blows oil around, and I chased other leads for a while before I figured out it was the pushrod tubes....the source isn't obvious. I used zip ties to attach a small wrap of fiberfax around the base of the suspect tubes and went flying for a bit. This revealed which tubes were leaking. Pulled the pushrods, removed tubes, replaced seals and reinstalled properly.
 
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Mine had a couple small leaks .. no big deal you'll just need to run them down .. mine ended up being the top case bolts, just needed the torque reset and some new star washers ..
 
Mine had a couple small leaks .. no big deal you'll just need to run them down .. mine ended up being the top case bolts, just needed the torque reset and some new star washers ..

All this joy can be yours for only forty thousand dollars...
 
How does Lycoming's warranty process work? Doesn't this become their issue to track down and fix?
 
I chased down a few leaks on my new engine and in doing so discovered Aeroshell mineral oil has dye in it that glows under a black light.


This. I started chasing leaks on mine by purchasing a kit of fluorescent dye, UV LED flashlight, and the goggles. I discovered quickly that the dye is not required. The oil fluoresces all by itself.
 
Oul leak apparently solved

My A&P texted me that he had found and corrected the oil leak in my new IO-390. He said it was leaking from an oil journal plug. Not sure what that is, but ill be picking the airplane up tomorrow and I hope he will explain it to me.

Happy camper.
 
I had the exact oil journal plug issue. There are small holes tapped into the case for ancillary purposes that are tapped and plugged with Allen head plugs. Mine was on the front face behind the prop governor.
My theory (I am not a mechanic) is that the metal of the plug is different than the case so they expand to heat and cooling differently thereby appearing tight on a cold engine, leaking during warm up, and then re-sealing up at full normal operating temp.
My symptom was leaking the same amount of oil onto the bottom cowl whether the flight was four hours or half an hour. Mechanics and assemblers are careful to not over torque the plugs because it can strip the case threads. (big Rut-roh). After many efforts to track down the problem, we got lucky and shut down right at the key temp where the plug which felt tight on a cold engine was finger loose on a warm one.
Some locktite and careful re-torquing solved the problem.
 
Oil journal plug leak

That was exactly the issue here. My mechanic made a video showing the weeping starting a few minutes after the engine starts then stopping as tge engine cools down. He put some loktite o a new slightly longer plug and torqued it down. The leak is gone!
 
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