Confused about Leaking Dual Mag

[Therookguy]

I just need a little help understanding where a small amount of oil is coming from that is showing up on the bottom of my dual mag. I don't understand how mags work very well so maybe someone can help. Here are the details:

Lycoming O-540-J3C5D

The mag was overhauled at 300 tach in Sep 2023. I have 359 Tach currently.

I had an A&P help me with an owner oil change, but I'm inexperienced so I spilled a ton of oil getting the filter off. As we were running the checks after swapping the oil he pointed out that the bottom of the mag and the mechanical fuel pump were covered in oil. It was about a handful amount. I told him it was probably oil that I spilled from removing the filter. We cleaned it and then ran it for a minute or two and the bottom of the mag was completely dry. I have since done a 1.0 and a 2.0 on it. On both flights there was a drop, literally a drop, of oil on the bottom of the Mag both before and 30 minutes after the flight. The engine has not consumed oil at all in the past 50 hours. The annual is fresh from October 2025. So here are my questions:

1. Is this a grounding item? I have two A&Ps that think it's a minimal issue and just watch it to see if it gets worse. I have another that thinks it's a larger concern and indicates that the mag needs to be overhauled.
2. I'm confused about the Mag leaking oil. I thought that there shouldn't be any oil in the mag at all and just wires and magnets? If there is oil getting into the mag somehow isn't that not good, especially considering it's a dual mag?
3. Is this something I should try to fix now considering I might be able to warranty it with the recent overhaul? or am I just going to spend hundreds of dollars trying to find where a drop of oil is coming from?

The engine runs totally fine just like it always has. So I'm mostly leaning towards watching it to see if it gets any worse. It's also possible the oil is coming from somewhere else and leaking down there.

 

[TCABM]

If the engine hasn’t burned any oil, that would indicate to me the oil you’re finding isn’t coming from inside the case.

I’m not a magneto expert either. @Jim K probably has better insight. B

 

[Gary Ward]

IMO, residual oil from your spill is what you're seeing.
Been there, done it. Spilled oil get's hot and drips off.

I use a 1.5-2 gal zip lock bag over the filter to keep it dry under the filter when I remove the filter. The whole filter goes in it when it comes off. i also use absorbent towels under the filter on top of the D mag.

 

[Jim K]

Remember that the magneto is gear driven, and the accessory case has a lot of oil moving around to lubricate those gears. There's an oil seal in the magneto. Oil inside the magneto isn't good, but I don't know that it's necessarily a grounding issue. I don't know enough about it to dispute the judgement of your a&p. Eventually it's probably going to contaminate the points. Most likely you're going to notice it on a mag check though, not fall out of the sky. OTOH, both your mags are in one case, so they're both affected, and you're justified in being nervous imo.

I suspect that at over two years since OH, whoever did it is going to tell you to pound sand. 30 hours a year is pretty low utilization, and i could see the seals getting dried out. They might swell back up with use. If it was mine I'd fly it for a while and see if it clears up.

You could also send it out for iran. I sent mine to Aircraft Accessories of OK last time. I paid the expedite fee and they turned it in 24 hours. Round trip under a week. Price was reasonable.

I'm just SGOTI. The real A&P's @Dan Thomas @Bell206 (I'm, probably forgetting some) should be along soon, and be able to speak better to how dangerous oil leaking through the mag is.

 

[Magman]

Engine oil contains particles and can short out the Contact Points. It’s worth

determining just what is going on.

I would remove the 4 plastic plugs and check for oil internally. Not

TOO difficult.

There are screws near the 4 corners of the mag that are used to attach

the harness. They are internal wrenching ( allen) and can be a pia to

remove. Particularly if there is little room from the firewall. Loosening

these will enable the harness to be pulled back. DO NOT DISCONNECT

INTERNAL LEADS. The idea is to see if there is oil IN the mag. If a lot it’s

time to pull the mag. If it’s just a little use a cotton swab to clean it up.

When reassembling the harness use CARE to avoid pinching internal leads

which would kill the shorted ( squeezed) side. You may want to repeat

after a few hours to see if it’s cured.


Note some “D-mags” have an AD on the Impulse Coupling that may be

Recurrent. There are 2 types of Springs for the IC. I replace either type

whenever the IC is removed for any reason.


NONE of this is Preventative Maintenance btw.

 

[Clip4]

When you make a mess changing oil, it takes a long time to get rid of it. Drops around or on the mag are not an issue. Due to air flows in the cowling, where you see drops doesn’t mean that’s where it originated, it’s where it is collecting. Another issue may be a leaking seal between the mag and the accessory case.

A tip on changing oil in the O540-J3C5D. When the engine is hot, there is a lot of oil in the filter. Drain the oil and leave the filter in place over night. Placard the pilot door no engine oil. The oil will drain from the filter overnight and there will be little left in the filter the next day. Then replace the filter and oil. I like to use small container under the filter to catch the 1-2 oz that comes out. A number of 4”x2”x3” plastic containers work well.

 

[Bell206]

1. Is this a grounding item? I have two A&Ps that think it's a minimal issue and just watch it to see if it gets worse. I have another that thinks it's a larger concern and indicates that the mag needs to be overhauled.
2. I'm confused about the Mag leaking oil. I thought that there shouldn't be any oil in the mag at all and just wires and magnets? If there is oil getting into the mag somehow isn't that not good, especially considering it's a dual mag?
3. Is this something I should try to fix now considering I might be able to warranty it with the recent overhaul? or am I just going to spend hundreds of dollars trying to find where a drop of oil is coming from?

1) Thats your call. But based on what you've described I tend to agree with the 1st two mechanics. However, if its still a concern, have one of those guys pull the mag cover and look inside for any traces of oil.
2) There shouldn't be any oil except the shaft oil applied during inspection. On the external areas, sure you could get a drop or two from various things to include dumping oil everywhere when changing a filter.
3) IMO, no on any OH.

 

[Therookguy]

Thanks everyone for the replies.

I'm mostly convinced that it's oil collecting there from the messy oil change. Thanks for the advice there.

Still I'll have my A&Ps take a look for at maximum an hour or two. That will run me about $200 for someone who is way more experienced than me mechanically to tell me that there's nothing wrong. I'll keep checking it every so often and if I'm getting more than a palm size of oil we'll dig further. Hopefully it's nothing and this thread dies here.