Based on the G100UL fuel leak thread what's your position?

[GeeBee]

Just now, Marc_B said:

do you have a link or the highlights?  Looks like it requires a subscription.

A fellow flew an A36 from KRHV to Ada, OK to KHPN and back. Transcontinental  trip on G100UL. Said any staining was cleaned off with simple green. Overall consumed 0.5 mph less because of the higher energy content at similar power settings. 

[GeeBee]

45 minutes ago, Marc_B said:

I'm not sure I follow your point here.  Do we use Skydrol for hydraulic fluid in our Mooney's?

Chemicals can be caustic.  Not surprising.  But if the statement is that 100LL is more dangerous for your paint/sealant/elastomers than G100UL, and that's not the case...that's a different issue.

I think that a lot of pilots have used 100LL on their belly's to degrease, to clean the engine, etc.  In the past I think that no one thought twice about a fuel splash on the top wing.  And a seeping wing was  something to monitor and consider patching when we "get to it" and and not cause for immediately addressing due to concern for paint damage.

For the fuels of the future, I don't think this will be the case.

Probably not, but using 100LL to clean your belly really? Would you use BBQ lighter fluid too? The point is a lot of fluids used in engines and airplanes peel paint. Not only Skydrol but most turbine engine oils peel paint although not as fast as Skydrol because of higher viscosity and lower di-ester content. But the comment was, is it ok for aircraft fluids to peel paint and the answer is emphatically....... Yes and the FAA approves it too.

[Marc_B]

38 minutes ago, GeeBee said:

But the comment was, is it ok for aircraft fluids to peel paint and the answer is emphatically....... Yes and the FAA approves it too.

But at the end of the day, none of us want our paint to be damaged or stripped unnecessarily and most will go to appropriate measures to prevent this. 

If its known how and when you'll see damage, and how to mitigate this then you can prevent it outside of catastrophic cases of damage or spill.  If the official word is that a product doesn't damage paint and you don't need to take mitigation steps, then that's an entirely different issue.

i.e. if the word was that G100UL will leak and strip paint if your sealant is over 20 years old or if you have a leak, then you might choose to either 1) not use it, 2) have tanks resealed prior, or 3) use at your own risk.  But the owner would assume a known risk.  But having a fuel advertised as 100% drop in across the fleet without any modification may be an overstatement. 

Continental gives pause, Lycoming gives pause, Textron gives pause, Cirrus gives pause.  This is a discussion about risk.  The producer is trying to minimize risk, some people are trying to magnify risk...but we're all trying to understand risk.

None of the Youtube videos or comments of this thread have better clarified this.  There may be risk to elastomers, there may be risk to paint, there may be risk to valve seats...so you either trust the FAA process and jump in, you try to understand the risk so you can hopefully mitigate it, or you just say no.  But FAA approval does not equal no risk.

Give it 20 years and hindsight will be 20:20.

[GeeBee]

I chose option 2.

 

[gabez]

for all of you that think G100UL has no issue, put your mouth where your money is, fly to KWVI or KRHV and fill your plane up then fly home. BTW I am still waiting for GAMI to give me a call as they stated via email. I offered to give them fuel that I sump from my tanks ..... crickets.....

[MikeOH]

42 minutes ago, GeeBee said:

Pretty simple. With Skydrol, if it leaks, it peels paint....period. Apparently, that is ok with everyone. If you walk down the concourse at any major airport you can spot all the leaking PCUs on the control surfaces. 

We are discussing PISTON powered GA aircraft.  I don't even know what PCU is?  Is leaking Skydrol even a thing with our piston powered aircraft?  I never even heard the topic of leaking Skydrol discussed here on MS.  Can you find an example of this being a problem for US??

[donkaye]

On 1/8/2025 at 8:13 AM, Marc_B said:

I'd be interested in hearing more from the people who have used and are using G100UL and haven't had any issues.  What type of paint do they have, what type of surface prep/wax/ceramic to they use, what is their fueling hygiene that they've found works, what's the age of the sealant and anything unique in their fuel system.

That might help as well.

I've been using G100UL intermittently, since I'm not based at KRHV.  I've experienced no operational change different from using 100LL other than the light staining I described earlier.  I intend to closely watch fueling in the future and not allow any matt to be placed on the wing.  As my plane has been hangared all its life, my paint is the original paint from Mooney.  I had my tanks resealed by Weep no More in November of 2016.  Since the plane is a 1991 model, that means 25 years to reseal.

[MikeOH]

25 minutes ago, donkaye said:

I've been using G100UL intermittently, since I'm not based at KRHV.  I've experienced no operational change different from using 100LL other than the light staining I described earlier.  I intend to closely watch fueling in the future and not allow any matt to be placed on the wing.  As my plane has been hangared all its life, my paint is the original paint from Mooney.  I had my tanks resealed by Weep no More in November of 2016.

What's the highest percentage of G100UL in your tank that you have used?  As I recall you have been mixing with 100LL.

[GeeBee]

45 minutes ago, MikeOH said:

We are discussing PISTON powered GA aircraft.  I don't even know what PCU is?  Is leaking Skydrol even a thing with our piston powered aircraft?  I never even heard the topic of leaking Skydrol discussed here on MS.  Can you find an example of this being a problem for US??

I simply pointed out many fluids in aviation peel paint, more do than not. I would also point out Prist peels paint and in the Mooney realm, yes anhydrous alcohol can peel paint. I just am pointing out that all kinds of fluids in aviation peel paint and yes the FAA says that is OK.

[Sabremech]

8 minutes ago, GeeBee said:

I simply pointed out many fluids in aviation peel paint, more do than not. I would also point out Prist peels paint and in the Mooney realm, yes anhydrous alcohol can peel paint. I just am pointing out that all kinds of fluids in aviation peel paint and yes the FAA says that is OK.

All of the fluids you mention “can” peel paint. It doesn’t necessarily mean it will. Do I care whether the FAA says it’s ok that it can peel paint? What does it matter that they supposedly say this? It would surely tick me off to no end that my $30k paint job gets screwed up by staining and possibly paint peeling. It sounds like you don’t care if your paint gets screwed up or not. The level of caring must be directly tied to your economic means to get it fixed. 

[EricJ]

2 hours ago, Marc_B said:

I'd be interested in hearing more from the people who have used and are using G100UL and haven't had any issues.  What type of paint do they have, what type of surface prep/wax/ceramic to they use, what is their fueling hygiene that they've found works, what's the age of the sealant and anything unique in their fuel system.

That might help as well.

The paint concerns are real because of the damage cases already reported and the mluvara vid that indicated that G100UL may be the cause of significant damage to paint.    Those are usually just cosmetic issues, although seriously damaging for owners, they are not usually a safey issue.    Tank leaks can always progress to be a safety issue, but that's not usually the first concern beyond the cosmetic damage.   Nevertheless, paint damage is a real and genuine concern for many or most owners.

My larger concern is with the effects on o-rings, gaskets, seals, hoses, and bladders made of materials that may react unfavorably to G100UL.   This is a signficant concernt to me because failures that can compromise safety or lead to a catstrophic in-flight system failure may take a long time to appear.   Excessive swelling can cause several different failure modes in o-rings, and degradation and longevity effects in hoses, gaskets, bladders, etc., are long-term effects that may not be evident for a while.   Engine fuel and oil hoses are usually changed out at engine overhaul, since general experience indicates failures due to use and aging will be caught by then, but if the aging is accelerated due to excessive swelling, I don't want people to learn the hard way that that's an issue.

I had already had concerns due to hints from GAMI about the formulation of G100UL, my concern was elevated by hearing George speak on the topic where he said G100UL may be harder on paint and materials, and my concerns were further amplified by the mluvara video.   I've learned to not trust the word of a new supplier/vendor/startup/whatever from long experience in industry, even when they have tons of "hard data", patents, and an approving regulator.   You really have to wait to hear the other sides of the story, and we haven't yet.   We don't hear from the competitors, although we may soon.  We have heard from Textron, who seems to share my concerns, but that was really just sort of a position paper with no technical backup (which is normal).   Since there isn't a long history of broad safe use, without more views into the other sides to the story or reliable independent analysis, I don't personally find any way to conclude that the risk to using the stuff is low, especially over the long term.

[GeeBee]

1 hour ago, Sabremech said:

All of the fluids you mention “can” peel paint. It doesn’t necessarily mean it will. Do I care whether the FAA says it’s ok that it can peel paint? What does it matter that they supposedly say this? It would surely tick me off to no end that my $30k paint job gets screwed up by staining and possibly paint peeling. It sounds like you don’t care if your paint gets screwed up or not. The level of caring must be directly tied to your economic means to get it fixed. 

No, Skydrol WILL peel paint. Period. It will also rearrange your fingerprints too.

Trust me, I have repainted more than one car in the employee lot at the departure end that got Skydrol rain.

It is clear few of you have read the Reddit link I posted about Skydrol

[Sabremech]

15 minutes ago, GeeBee said:

No, Skydrol WILL peel paint. Period. It will also rearrange your fingerprints too.

Trust me, I have repainted more than one car in the employee lot at the departure end that got Skydrol rain.

It is clear few of you have read the Reddit link I posted about Skydrol

I’m well aware of what Skydrol can do as I have worked with it in the past. It doesn’t have the effect you say it does on the corporate aircraft that I’ve maintained that have it. I still have Castor Oil in the top drawer of my toolbox. It’s clear you feel that you know more than many other members of this forum.

[George Braly]

38 minutes ago, EricJ said:

 

My larger concern is with the effects on o-rings, gaskets, seals, hoses, and bladders made of materials that may react unfavorably to G100UL.   This is a signficant concernt to me because failures that can compromise safety or lead to a catstrophic in-flight system failure may take a long time to appear.   Excessive swelling can cause several different failure modes in o-rings, and degradation and longevity effects in hoses, gaskets, bladders, etc., are long-term effects that may not be evident for a while.   Engine fuel and oil hoses are usually changed out at engine overhaul, since general experience indicates failures due to use and aging will be caught by then, but if the aging is accelerated due to excessive swelling, I don't want people to learn the hard way that that's an issue.

Since there isn't a long history of broad safe use, without more views into the other sides to the story or reliable independent analysis, I don't personally find any way to conclude that the risk to using the stuff is low, especially over the long term.

 

When is "good enough" - - good enough?   

1) 14 years of use in a Cirrus fiberglass wing / fuel tank , with standard Continental fuel system (electric boost pump/ hoses / fittings/ fuel selector / engine driven fuel pump / fuel filter / fuel gascolater /  - - -  AND ALL OF THE STANDARD O-RINGS, GASKETS, DIAGHPRAMS , SEALS,  etc etc etc associated with the OEM system. 

RESULT:   No drips.  No leaks.  No paint stain.   No sealant issues.    

If that is not "good enough" - - then how much is ?  

2)  Nearly one year and 200 hours of fully independent testing done by Embry Riddle.  C 172.   with standard LYCOMING  fuel system ( hoses / fittings/ fuel selector / engine driven fuel pump / fuel filter / etc etc /  - - -  AND ALL OF THE STANDARD O-RINGS, GASKETS, DIAGHPRAMS , SEALS,  etc associated with the OEM system. 

All of those components disassembled and inspected by ERAU and by the FAA - - independent of any involvement by GAMI.

RESULT:   No drips.  No leaks.  No paint stain.   No sealant issues.   ALL components were deemed to be fully airworthy.

3)  12 months and ~ 200 hours in a Baron with one 46 year old fuel bladder and one 50 year old fuel bladder.  One with G100UL and the other with 100LL.  BOTH leaked.   The 100LL bladder leaked after about two weeks of exposure.  The G100UL bladder after about eight months.  Both had multiple internal pre-existing repairs and multiple pin-hole air-leaks. Otherwise, no issues with the operation of the two Baron engines.  In addition: 

     Repetitive OIL samples document that engine wear metals decreased by ~ 50% on G100UL vs 100LL; 

     Repetitive bore scope inspections reveal no valve seat issues; 

     Repetitive spark plug inspections reveal the G100UL side spark plug electrodes remained free of any deposits and the 100LL side had "generous" deposits on the electrodes and required servicing. 

4)  A 1944 Douglas A-26 "Invader" has had G100UL in those fuel tanks for over seven months.  No drips. No leaks.  No paint stains. 

                          *********

When is "good enough" - - good enough?     

                          ********* 

Observation: 

One Mooney fuel tank repair shop manager recently told me that, based on his experience, 80-90% of the Mooney fuel tanks he works on have had improper repairs to those tanks.  Often with the wrong repair sealant. 

George

[GeeBee]

1 hour ago, Sabremech said:

I’m well aware of what Skydrol can do as I have worked with it in the past. It doesn’t have the effect you say it does on the corporate aircraft that I’ve maintained that have it. I still have Castor Oil in the top drawer of my toolbox. It’s clear you feel that you know more than many other members of this forum.

Because most corporate aircraft have a Skydrol resistant clear coat such as Imron AF740. I say resistant, meaning you got about 24-48 hours to clean it up, which usually happens in corporate aircraft. Put Skydrol on most finishes without a clear coat like airliners and the paint is toast right now.

[EricJ]

7 minutes ago, George Braly said:

 

When is "good enough" - - good enough?   

1) 14 years of use in a Cirrus fiberglass wing / fuel tank , with standard Continental fuel system (electric boost pump/ hoses / fittings/ fuel selector / engine driven fuel pump / fuel filter / fuel gascolater /  - - -  AND ALL OF THE STANDARD O-RINGS, GASKETS, DIAGHPRAMS , SEALS,  etc etc etc associated with the OEM system. 

RESULT:   No drips.  No leaks.  No paint stain.   No sealant issues.    

If that is not "good enough" - - then how much is ?  

2)  Nearly one year and 200 hours of fully independent testing done by Embry Riddle.  C 172.   with standard LYCOMING  fuel system ( hoses / fittings/ fuel selector / engine driven fuel pump / fuel filter / etc etc /  - - -  AND ALL OF THE STANDARD O-RINGS, GASKETS, DIAGHPRAMS , SEALS,  etc associated with the OEM system. 

All of those components disassembled and inspected by ERAU and by the FAA - - independent of any involvement by GAMI.

RESULT:   No drips.  No leaks.  No paint stain.   No sealant issues.   ALL components were deemed to be fully airworthy.

3)  12 months and ~ 200 hours in a Baron with one 46 year old fuel bladder and one 50 year old fuel bladder.  One with G100UL and the other with 100LL.  BOTH leaked.   The 100LL bladder leaked after about two weeks of exposure.  The G100UL bladder after about eight months.  Both had multiple internal pre-existing repairs and multiple pin-hole air-leaks. Otherwise, no issues with the operation of the two Baron engines.  In addition: 

     Repetitive OIL samples document that engine wear metals decreased by ~ 50% on G100UL vs 100LL; 

     Repetitive bore scope inspections reveal no valve seat issues; 

     Repetitive spark plug inspections reveal the G100UL side spark plug electrodes remained free of any deposits and the 100LL side had "generous" deposits on the electrodes and required servicing. 

4)  A 1944 Douglas A-26 "Invader" has had G100UL in those fuel tanks for over seven months.  No drips. No leaks.  No paint stains. 

                          *********

When is "good enough" - - good enough?     

                          ********* 

A product that has been field deployed to a large number of users for a significant amount of time can give one confidence that the product may be safe.  The larger the user base and longer the deployment experience, the more confidence might be increased.   What you've listed above is a tiny, miniscule amount of testing with a tiny, miniscule number of test platforms compared to what the fuel would experience in a full field deployment.   The number of diverse platforms, maintenance conditions, and operating conditions that the fuel could experience in a full deployment would be far beyond the testing that you just outlined above by orders of magnitude.   It is always expected that field conditions may expose issues beyond what were tested for most products, regardless of how much testing was done or the quality of the testing.

When people say that they'll wait until something has been out for a while before they try it, this is what they mean.    People who say not to buy a new car model in the first year understand this as well.   Similar with new medications.
 

7 minutes ago, George Braly said:

Observation: 

One Mooney fuel tank repair shop manager recently told me that, based on his experience, 80-90% of the Mooney fuel tanks he works on have had improper repairs to those tanks.  Often with the wrong repair sealant. 

George

It's not limited to Mooneys, as much as you seem to like disparaging their tank maintenance in particular.   The GA fleet has a large diversity and variation of construction techniques, maintenance practices, substituted materials, modifications, vintage maintenance adaptations, and aging and condition issues, some proper and some less so, and that's just the certificated fleet.   Experimentals, of which there are many, also fly in the same sky from the same airports and carry people we know and like, and may have even more variation.   Your list of tested conditions is nice, but it doesn't represent anything close to a full sampling of conditions that the product will see in the field.   This is not unusual in product development, it is just the reality of the situation.

How much testing is enough will be different for everybody, as evidenced by the dialogues here.   

[MikeOH]

8 minutes ago, GeeBee said:

Because most corporate aircraft have a Skydrol resistant clear coat such as Imron AF740. I say resistant, meaning you got about 24-48 hours to clean it up, which usually happens in corporate aircraft. Put Skydrol on most finishes without a clear coat like airliners and the paint is toast right now.

What is your obsession with Skydrol???  I don't give a damn if it eats paint for breakfast, lunch, and dinner, nor that the FAA approves of the menu!

I care if G100UL eats my paint when I KNOW 100LL does NOT eat my paint.  Why is this so hard for you to acknowledge as a VALID concern for owners of planes with less than perfect paint?  We do NOT want a problem that we have never had.

[George Braly]

3 minutes ago, EricJ said:

A product that has been field deployed to a large number of users for a significant amount of time can give one confidence that the product may be safe.  The larger the user base and longer the deployment experience, the more confidence might be increased.   What you've listed above is a tiny, miniscule amount of testing with a tiny, miniscule number of test platforms compared to what the fuel would experience in a full field deployment.   

 

As I interpret your certification / approval standards: 

Boeing,  Airbus, Cessna, Piper, Cirrus etc would have to take a newly designed aircraft and put it into service with empty cabins and fly multiple versions around for thousands of hours and years - - before they could ever allow the airlines or the private pilots to accept delivery and begin service with passengers on board.  

[GeeBee]

7 minutes ago, MikeOH said:

What is your obsession with Skydrol???  I don't give a damn if it eats paint for breakfast, lunch, and dinner, nor that the FAA approves of the menu!

I care if G100UL eats my paint when I KNOW 100LL does NOT eat my paint.  Why is this so hard for you to acknowledge as a VALID concern for owners of planes with less than perfect paint?  We do NOT want a problem that we have never had.

Because all the fluids we use eat paint, some more quickly than others depending upon the paint. I have some paint damage (factory paint job) on my underwing from 100LL which is the reason why I took the airplane to WetWingologists for a complete and professional re-seal. The best avoidance for fuel induced paint damage is a tight fuel system.

[MikeOH]

1 minute ago, GeeBee said:

Because all the fluids we use eat paint, some more quickly than others depending upon the paint. I have some paint damage (factory paint job) on my underwing from 100LL which is the reason why I took the airplane to WetWingologists for a complete and professional re-seal. The best avoidance for fuel induced paint damage is a tight fuel system.

Since you stubbornly refuse to acknowledge that concern over G100UL being more aggressive than 100LL is a legitimate concern, then would it be okay with you if any new fuel was as aggressive as Skydrol?  Since, it appears your position is that owners should spend whatever money it takes to prevent ANY leaks or spills, thus rendering any concerns over fuel eating paint moot?  Is that your position?

[MikeOH]

@George Braly

After your latest post above I feel compelled to ask for, I believe, the third time what were the seals and O-ring materials in the test Cirrus and Embry-Riddle C172?

[EricJ]

1 minute ago, George Braly said:

As I interpret your certification / approval standards: 

Boeing,  Airbus, Cessna, Piper, Cirrus etc would have to take a newly designed aircraft and put it into service with empty cabins and fly multiple versions around for thousands of hours and years - - before they could ever allow the airlines or the private pilots to accept delivery and begin service with passengers on board.  

You may have skipped the last line of my post.

Beyond that, I spent part of my career developing avionics for airliners.   The amount of review, scrutiny, testing, and oversight applied to airliner development before the first prototype is even built dwarfs what you described above by a large margin. 

Additionally, Boeing, Airbus, Cessna, Piper, Cirrus, etc., have long histories of product deployments and use histories, so there is substantial basis for levels of safety confidence in each.   G100UL and GAMI do not have any significant history in deploying fuels for public use.   It is an unknown quantity, so field performance and developer behavior can make a difference in how people assess the associated risk.    We've seen over the years that companies like Airbus and Boeing had significant field failures and the nature of those failures and how the developers responded have had a significant impact on how people assess the risks associated with each.   I remember when the saying was, "If it's not Boeing, I'm not going", to now the first 'not' has been dropped.   

Everybody decides on their own how much testing is enough or whether something is sufficiently safe.

[MikeOH]

1 hour ago, George Braly said:

 

When is "good enough" - - good enough?   

If that is not "good enough" - - then how much is ?  

                          *********

When is "good enough" - - good enough?     

                          ********* 

Observation: 

One Mooney fuel tank repair shop manager recently told me that, based on his experience, 80-90% of the Mooney fuel tanks he works on have had improper repairs to those tanks.  Often with the wrong repair sealant. 

George

You know there's an old joke that in the GE company, the 'GE' stood for Good Enough!  It was NOT a compliment.

The problem with your position is that we presently have a fuel, 100LL, that does NOT permanently stain (you would not have issued your 'handling' bulletin if there wasn't some truth that G100UL is worse), does NOT swell seals or O-rings, and costs LESS!

The problem I, and some others have, is that G100UL is WORSE in those parameters.  So, "when is 'good enough' - - good enough?"? When the new product is not worse, that's when!

[GeeBee]

27 minutes ago, MikeOH said:

Since you stubbornly refuse to acknowledge that concern over G100UL being more aggressive than 100LL is a legitimate concern, then would it be okay with you if any new fuel was as aggressive as Skydrol?  Since, it appears your position is that owners should spend whatever money it takes to prevent ANY leaks or spills, thus rendering any concerns over fuel eating paint moot?  Is that your position?

Uh I believe you are putting words in my mouth. I doubt any fuel would be as aggressive as Skydrol since fuel is not di-ester based. However a new fuel may necessitate some higher level of maintenance, just as boat owner had to do with added ethanol. I had to replace all my fuel lines for instance. I do believe in nice and tight fuel systems. which is why I resealed my tanks even though the weeping was in the "permissible" zone. I know there is "permissible" tank leakage, but I'm not a fan of flying a giant Van Der Graff generator seeping fuel. Call me crazy. It may be very likely you will have to reseal your tanks and replace a few o-rings to accept the new fuel, just like you had to get a transponder, then an encoder, then ADS-B and if you are Canadian, a diversity set up. Things change and sometimes you have to spend money if you want to keep flying the plane of your choice.

[Justin Schmidt]

9 minutes ago, MikeOH said:

You know there's an old joke that in the GE company, the 'GE' stood for Good Enough!  It was NOT a compliment.

The problem with your position is that we presently have a fuel, 100LL, that does NOT permanently stain (you would not have issued your 'handling' bulletin if there wasn't some truth that G100UL is worse), does NOT swell seals or O-rings, and costs LESS!

The problem I, and some others have, is that G100UL is WORSE in those parameters.  So, "when is 'good enough' - - good enough?"? When the new product is not worse, that's when!

Please share the actual scientific/engineering data that g100ul causes problems.