1967 M20F: Prop Grease Leak?

[PierceM20F]

Hi all, I’ve got a 1967 M20F with an engine/prop at about 270 SMOH. I’ve put about 70 hours on it since September ‘21 when I bought it. The other day, I noticed what I thought to be a large bug splatter on the prop (I fly out of Tulsa, OK) so I cleaned it off. A couple flights later, I noticed it again, so I investigated further and saw it was about a 1” section of very sticky substance, gold ish in color, coming from the prop (see pictures). It happened to have been getting colder than anything I had flown it in so far this season. 40’s. I had assumed it was because I didn’t let the engine warm up enough before cycling the prop (I cycle the prop 3 times). Flew the airplane again for maybe 5 hours no repeat on the issue. After getting home tonight from a flight (high 30’s outside), I noticed the beginnings of the same type of streak on the prop. I let the engine warm up to 120 degrees F on the oil temp before doing my run up and prop cycle. Anyone have any thoughts on this? I’m concerned it needs a reseal but I’m also skeptical as it’s a low time prop (270 hours since overhaul) and it’s not oil coming out of the prop. Any help is appreciated. I’m also new to ownership to apologies if my understanding of the details of the prop is not up to par. Still learning. Thanks! 

[Shadrach]

What was the overhaul date? Assuming it’s a Hartzell, it may have been filled with new Aeroshell 6 formulation that separates and is causing issues throughout the industry.  Engine temp has almost no affect on the temp of the prop or the grease within. That being said, separated Aeroshell 6 manifests as liquid on the prop and is not typically globular (at least not the new formula). If you have globs (it looks that way in the pics) there is a chance the the seal has herniated. Was the prop serviced recently?

Edited November 14, 2021 by Shadrach

[PierceM20F]

The prop was overhauled in 2014 and I had a prebuy/annual when I bought the airplane in September of this year. Everything checked out then. I’m monitoring it but I’m just not sure if this is a huge problem or if the cold weather has anything to do with it? The plane only flew maybe 40 hours a year before me and I’m flying 20 hours a month now. 

[Ragsf15e]

42 minutes ago, PierceM20F said:

The prop was overhauled in 2014 and I had a prebuy/annual when I bought the airplane in September of this year. Everything checked out then. I’m monitoring it but I’m just not sure if this is a huge problem or if the cold weather has anything to do with it? The plane only flew maybe 40 hours a year before me and I’m flying 20 hours a month now. 

The temps you mention aren’t cold and wouldn’t affect the prop as @Shadrach mentioned.  Sure looks like prop grease but we can ask our prop guy @Cody Stallings.  
It is good to let your engine warm up at idle before runup, 100 degrees oil temp is a common number people use.  Im in Washington state, so much colder than you, but I’m always at 100+ by the time I hit the runup area.  Unless you runup immediately after start, I doubt you need to worry too much about letting it warm (but you are right to verify it). A short taxi usually does it since your cooling airflow is limited on the ground.

[PierceM20F]

Okay that’s good to know regarding the weather temps. I will note that the grease is not coming from the zirks (spelling?). I’ll be curious to see what Cody says. 

[Shadrach]

2 hours ago, PierceM20F said:

The prop was overhauled in 2014 and I had a prebuy/annual when I bought the airplane in September of this year. Everything checked out then. I’m monitoring it but I’m just not sure if this is a huge problem or if the cold weather has anything to do with it? The plane only flew maybe 40 hours a year before me and I’m flying 20 hours a month now. 

I think the issues with Aeroshell 6 came after 2014. Sometimes props will shed a blob of grease. Clean it off thoroughly and check it in a few hours.

[Skates97]

I had the same thing in 2018. I ended up flying it a bit longer and then getting it resealed. the prop shop wanted to do an overhaul because of the time since new. After talking with them he said he would take a look at it when he got it and if he could just reseal it instead of overhaul he would. It was a new prop, new hub, never cracked open before and he ended up just re-sealing it and has been trouble free since.

 

[MikeOH]

I've told this story here before...I've had this issue since I first got my plane.  First, I sent the prop in for reseal and they accidentally overhauled it (but only charged me for a reseal since it was their mistake) but it still leaked...sent it back and they resealed it for free,....still leaked!   I lived with it as I had become educated by then about the problems with Aeroshell 6.  I bought some Aeroshell 5 and at last annual had my A&P/IA add the Aeroshell 5 (mixing Aeroshell 5 and 6 is now OK per a recent Hartzell SB; excerpt below).  Yeah, it still leaks, but not nearly as much.  My plan is to keep 'topping off' with Aeroshell 5 at each annual and hope it improves even more.  Meanwhile I just live with wiping down the prop

 

[DXB]

20 hours ago, PierceM20F said:

 

 

I think I've had the liquifying Aeroshell #6 slowly leaking out onto one of my two Hartzell blades for a few years now.  I'm just watching it because when I pump Aeroshell #5 into the hub periodically, grease comes out immediately from the opposite fitting with the first or second squirt, so I'm very confident the hub isn't about to run dry. One shouldn't try to flush the old grease out aggressively because the pressure of a grease-packed hub may really trash the seals during operation. Just pump until it comes out the opposite fitting or 5-6 squirts, whichever comes first.  I think there is a good Youtube video from Hartzell on this somewhere.

However mine is just a subtle sheen visible only on the inner surface of one blade, only just near the hub, and mainly in the hot summer months.  That is WAY more grease than I've ever seen coming past my seals, and I'd worry that if it keeps up, you're gonna need a reseal job pretty soon or risk trashing your hub.  Since the prop is low time, my worry would be that some ham-handed A&P already aggressively pumped your hub full of grease and thus totally trashed the seals.  

[Shadrach]

8 hours ago, MikeOH said:

I've told this story here before...I've had this issue since I first got my plane.  First, I sent the prop in for reseal and they accidentally overhauled it (but only charged me for a reseal since it was their mistake) but it still leaked...sent it back and they resealed it for free,....still leaked!   I lived with it as I had become educated by then about the problems with Aeroshell 6.  I bought some Aeroshell 5 and at last annual had my A&P/IA add the Aeroshell 5 (mixing Aeroshell 5 and 6 is now OK per a recent Hartzell SB; excerpt below).  Yeah, it still leaks, but not nearly as much.  My plan is to keep 'topping off' with Aeroshell 5 at each annual and hope it improves even more.  Meanwhile I just live with wiping down the prop

 

Be careful doing that.  You’ve added some 5, might be best to leave it alone. If you keep servicing it, eventuality it will accumulate enough grease to herniate the seals when the prop is cycled. I had an informative conversation with Shawn Young at East Coast Propellers back in August. They have seen a lot of leaky props due to the new formulation of Aeroshell but non that have suffered from lack of lubrication.

[PierceM20F]

Well, it seems we have all had quite a few different experiences and outcomes. It's a very small amount and it only happens on some flights. I flew yesterday upwards of 4 hours total and I only noticed it show up on one of the flights after about an hour of run time. Since the prop is only 270 SMOH, I'm just going to monitor it. I'll bring it up at annual in August of next year (assuming everything continues going well). The plane had an annual/prebuy in Morganton, NC with AGL services Lynn Mace who seems to be quite popular among the Mooney community for maintenance. What I don't want to do is send it in for a re seal and then it continues to do the same thing. If it gets a lot worse where the grease starts coating a lot of the blade every time I fly it, I'll reconsider. Thanks all for the input, I've learned a lot!

[MikeOH]

13 hours ago, Shadrach said:

Be careful doing that.  You’ve added some 5, might be best to leave it alone. If you keep servicing it, eventuality it will accumulate enough grease to herniate the seals when the prop is cycled. I had an informative conversation with Shawn Young at East Coast Propellers back in August. They have seen a lot of leaky props due to the new formulation of Aeroshell but non that have suffered from lack of lubrication.

Thanks for the warning, but I'm well aware of the dangers of over doing it and rupturing the seals.  I'm just talking about the normal annual maintenance where two of the zerks are removed and a small amount of fresh grease is pumped in until a bit comes out where the zerks were installed.

[Cody Stallings]

Looks like grease coming down the blade.

May have a reseal in your near future.

While having it done ask your shop to comply with SL #293 Rev 1.

ghats the use of the Turbo Prop blade Orings, they tend to last forever 

[MikeOH]

1 hour ago, Cody Stallings said:

Looks like grease coming down the blade.

May have a reseal in your near future.

While having it done ask your shop to comply with SL #293 Rev 1.

ghats the use of the Turbo Prop blade Orings, they tend to last forever 

@Cody Stallings

Would you recommend using the new NYCO grease vs. Aeroshell?

[Cody Stallings]

1 hour ago, MikeOH said:

@Cody Stallings

Would you recommend using the new NYCO grease vs. Aeroshell?

I personally lean towards #5 after years of experience with it. The NYCO is brand new an the jury is still out. Seems to de doing good so far though.

Now that Aeroshell Grease is almost unobtainable, we may only have NYCO to use pretty soon.

[Pete M]

Try not cylcling the prop or do just a very light cycle before t/o and see if the leak stops. If it didnt fly much could the seals have dried or shrunk? Either way, its been 7 years so a reseal wouldnt be wasted money imo.

[Marauder]

Well, it seems we have all had quite a few different experiences and outcomes. It's a very small amount and it only happens on some flights. I flew yesterday upwards of 4 hours total and I only noticed it show up on one of the flights after about an hour of run time. Since the prop is only 270 SMOH, I'm just going to monitor it. I'll bring it up at annual in August of next year (assuming everything continues going well). The plane had an annual/prebuy in Morganton, NC with AGL services Lynn Mace who seems to be quite popular among the Mooney community for maintenance. What I don't want to do is send it in for a re seal and then it continues to do the same thing. If it gets a lot worse where the grease starts coating a lot of the blade every time I fly it, I'll reconsider. Thanks all for the input, I've learned a lot!

Mine started out as “sometimes” event as well. Unfortunately not many things in aviation fix themselves…





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[Nstarbf]

i just got done remedying this problem on my 62 C.  Your pictures look familiar.  The prop ended up needing to be resealed.   

[PierceM20F]

I had a mechanic take a look and in his opinion it was overgreased. He said to just watch it and if it gets worse, re-evaluate. Time will tell! 

[Browncbr1]

Make sure it isn’t just a little dob of grease that came off the zerk after annual.  The PU zerk covers sometimes hold a little grease.   Sometimes a little blob will come off and hit the inside of the spinner and eventually come off on the prop.     

[RobertGary1]

Yea if it was just after annual I’d just ignore it. Easy to leave a little bit stet servicing and it makes a big mess. 

[Jsno]

As long as it has been since it was serviced, I would get a reseal with NYCO grease.  When it is cold the aeroshell 5 is not viscous enough to allow the prop to move properly when you change pitch. 

[MikeOH]

4 hours ago, Jsno said:

As long as it has been since it was serviced, I would get a reseal with NYCO grease.  When it is cold the aeroshell 5 is not viscous enough to allow the prop to move properly when you change pitch. 

Yeah, but at -40 I don't move properly, either  And, right now, lowest I could find in the US is -35 at 18,000'...in Montana.  So, I'm just not that worried about the Aeroshell #5 grease's 'performance' difference!

[Jsno]

Sounds like you have it figured out.