Chris K Posted October 4, 2022 Report Posted October 4, 2022 So this past weekend one of the wing fuel sight gages decided it no longer liked being affixed to the wing and just departed the aircraft. Upon inspection, it looks like nothing holds these in place other than plain silicone. Just ordered a new one to the tune of some 145 dollars. My question is has anyone figured out a better glue to use other than silicone in order to not lose again? If silicone is sufficient, how much to put in there to make it both stay and work properly? It appears that whomever siliconed previously did so while leaving an orifice in the center of the silicone - not sure if that was done for function of the magnetic gage or simply installer preference.
Pinecone Posted October 4, 2022 Report Posted October 4, 2022 You could probably use a urethane mastic (3M 5200) that would stick down better than silicone. But, it would make it hard to remove if you needed to do so. You can remove items attached with urethane mastic by running a thin wire through the joint to cut it, but with the fuel capsule recessed, it is hard to do that.
PT20J Posted October 4, 2022 Report Posted October 4, 2022 RTV is actually a pretty good adhesive. I would avoid any voids because if water gets in a void it could freeze and since water expands when it freezes it might break the seal.
N201MKTurbo Posted October 4, 2022 Report Posted October 4, 2022 RTV is your best bet. Clean out all the old stuff and sand out the corrosion. They get corroded because people don't use enough RTV. Mask around the hole and the top of the indicator capsule. Fill the hole with a generous amount of RTV. You don't want any voids, that's how you get corrosion. Push the capsule into the RTV until it seats into the hole. Make sure it aligns with the tab and is seated into the tab. DON'T TRY TO CLEAN UP THE EXTRUDED RTV! Just leave it be, go home and let it cure overnight. Come back the next day and peal off the extruded RTV, remove the masking tape, clean up any excess RTV with your fingernail. Enjoy your new capsule. One reason to use RTV is so you can remove it later if you have to.
N201MKTurbo Posted October 4, 2022 Report Posted October 4, 2022 Holy crap, I wrote almost the exact same thing back in '18. 1
N201MKTurbo Posted October 4, 2022 Report Posted October 4, 2022 An easy way to mask the wing and the capsule is to just set the capsule in place and then mask over the wing and capsule. then cut the capsule out with an X-acto knife.
ohdub Posted October 4, 2022 Report Posted October 4, 2022 @M20Doc just put a new one on my plane last week. He could tell you what to use.
Guest Posted October 4, 2022 Report Posted October 4, 2022 2 hours ago, N201MKTurbo said: RTV is your best bet. Clean out all the old stuff and sand out the corrosion. They get corroded because people don't use enough RTV. Mask around the hole and the top of the indicator capsule. Fill the hole with a generous amount of RTV. You don't want any voids, that's how you get corrosion. Push the capsule into the RTV until it seats into the hole. Make sure it aligns with the tab and is seated into the tab. DON'T TRY TO CLEAN UP THE EXTRUDED RTV! Just leave it be, go home and let it cure overnight. Come back the next day and peal off the extruded RTV, remove the masking tape, clean up any excess RTV with your fingernail. Enjoy your new capsule. One reason to use RTV is so you can remove it later if you have to. We’re you in my shop last week when I was installing one for @ohdub
mooniac15u Posted October 5, 2022 Report Posted October 5, 2022 15 hours ago, M20Doc said: We’re you in my shop last week when I was installing one for @ohdub Where were you able to find one?
Guest Posted October 5, 2022 Report Posted October 5, 2022 7 hours ago, mooniac15u said: Where were you able to find one? From Mooney, we’re an MSC
Shadrach Posted October 6, 2022 Report Posted October 6, 2022 2 hours ago, M20Doc said: From Mooney, we’re an MSC Did you have them in stock or did Mooney send them to you recently?
Guest Posted October 6, 2022 Report Posted October 6, 2022 9 minutes ago, Shadrach said: Did you have them in stock or did Mooney send them to you recently? They took several months to get from Mooney.
Chris K Posted November 2, 2024 Author Report Posted November 2, 2024 On 10/4/2022 at 4:16 PM, N201MKTurbo said: Mask around the hole and the top of the indicator capsule. Fill the hole with a generous amount of RTV. You don't want any voids, that's how you get corrosion. Push the capsule into t Just realized I never followed up on this topic. 2 years later and followed this procedure - no issues since. Left no voids which meant cleaning up left over RTV afterward pushing the guage in place. The cleanup was fairly easy as any excess dry RTV on the wing will just break away from painted surfaces by rolling your finger over. 1 1
dkkim73 Posted November 2, 2024 Report Posted November 2, 2024 1 hour ago, Chris K said: Just realized I never followed up on this topic. 2 years later and followed this procedure - no issues since. Left no voids which meant cleaning up left over RTV afterward pushing the guage in place. The cleanup was fairly easy as any excess dry RTV on the wing will just break away from painted surfaces by rolling your finger over. Same here a few months ago. Completely filling the space with RTV is the key. I took the additional advice of a piece of 3M clear repair tape over the top. Good insurance.
JimK Posted November 23 Report Posted November 23 After RTVing my replacement site guage into the hole as people have described, I allowed the RTV to cure, then I cleaned the area with alcohol and then cut a 3” circle of automotive Paint Protective Film (PPF) and installed it centered over the guage. Whether the RTV fails or not, that guage is not coming out in flight any more. Guaranteed! 2
aidanglover444 Posted November 26 Report Posted November 26 I am actually dealing with the same issue right now. My sight gauge also separated and it looks like it was held in place with nothing more than silicone. I am wondering if anyone has found an adhesive that holds better or if silicone is really the recommended option and just needs to be applied differently. Any guidance on how much to use, especially regarding that center opening, would be very helpful
LANCECASPER Posted November 26 Report Posted November 26 7 hours ago, aidanglover444 said: I am actually dealing with the same issue right now. My sight gauge also separated and it looks like it was held in place with nothing more than silicone. I am wondering if anyone has found an adhesive that holds better or if silicone is really the recommended option and just needs to be applied differently. Any guidance on how much to use, especially regarding that center opening, would be very helpful Read further up on this post and you'll see that RTV is suggested.
Fly Boomer Posted November 26 Report Posted November 26 9 hours ago, aidanglover444 said: Any guidance on how much to use Something else you can read in this and other threads on MooneySpace is to use so much that there is zero room for an air space. I have not done this yet, but the consensus seems to be that the RTV should squish out when you push the gauge into the depression in the top of the wing. If there is any room for an air space, water seems to form under the gauge, and when it freezes, it can push the gauge out. Frequently at high altitude.
Pinecone Posted November 26 Report Posted November 26 If you really want it to not come out there is 3M 5200. It is a urethane mastic. Purchase at Home Depot (paint area) or boating supply place. The problem is getting it out of you ever need to. About the only way is to cut the mastic, usually with a fine fire pulled through the joints
dkkim73 Posted November 26 Report Posted November 26 9 hours ago, Fly Boomer said: Something else you can read in this and other threads on MooneySpace is to use so much that there is zero room for an air space. I have not done this yet, but the consensus seems to be that the RTV should squish out when you push the gauge into the depression in the top of the wing. If there is any room for an air space, water seems to form under the gauge, and when it freezes, it can push the gauge out. Frequently at high altitude. This. The one I replaced previously was hard, though not insane, to remove. Potting it with RTV was my approach. The factory (or at least prior) one came out with the covering tape...
dkkim73 Posted November 26 Report Posted November 26 On 11/23/2025 at 4:44 PM, JimK said: After RTVing my replacement site guage into the hole as people have described, I allowed the RTV to cure, then I cleaned the area with alcohol and then cut a 3” circle of automotive Paint Protective Film (PPF) and installed it centered over the guage. Whether the RTV fails or not, that guage is not coming out in flight any more. Guaranteed! I might try that. Used 3M clear tape last time.
dkkim73 Posted November 28 Report Posted November 28 Next steps in the process. Got some silicone/caulk remover from Ace (a goo-gone variant, I also thought about MEK), cleaned the pockets, then with isopropyl alcohol. Made masking tape masks with cut-outs at home (laid up on zip-lock bags), also masked the dial faces, and then laid them up with silicone in the hangar. Given my understanding that oxygen starts the cure, I did a thin coat on both surfaces first, then filled the space from the middle (to prevent air pockets). Then I inserted the capsules... It took a suprising amount of force to expel the extra silicone. 1
dkkim73 Posted November 28 Report Posted November 28 On 11/26/2025 at 4:24 PM, dkkim73 said: the consensus seems to be that the RTV should squish out when you push the gauge into the depression in the top of the wing. If there is any room for an air space, water seems to form under the gauge, and when it freezes, it can push the gauge out. Frequently at high altitude. I agree with this 100%. The last gauge I installed with this method was a devil to remove (see photo of the Vlad Tepes earlier in the thread). The other (factory?) gauges popped right out, one with flight and the other with tape... So I went with the "lots of silicone" method earlier today. 1
PT20J Posted November 29 Report Posted November 29 On 11/26/2025 at 3:51 AM, LANCECASPER said: Read further up on this post and you'll see that RTV is suggested. IPC calls for RTV 108. 1
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