What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

fuel residue in tank

dick seiders

Well Known Member
I am in the process of upgrading my fuel tank to the latest frangible bolt mod. (13-12-19 I think). I had completed my 2013 Cond. Insp. just prior so am catching up now. I decided to remove the top skin as someone in the forum suggested some time ago so I wouldn't have to go nuts trying to do the work thru the sending unit door.
After removing the skin I noticed a gray colored coating on the bottom of the tank. I can easily wipe it off, but I am curious as to it's identity. The coating showed fuel trace marking from draining the tank yesterday which suggests the stuff is moving around with the fuel, but it dried as the fuel evaporated after draining tank. Now that it has dried it will stick to your fingers if you rub them on the tank bottom skin and the dried material is very fine powder in appearance. Very interesting. Does this residue burn with the fuel? If so is that a good thing? I guess the answer there is it depends what it's from. Do any of you know what it might be? Has anyone else seen the stuff?
Thanks for any feedback.

note: If there are more out there that have not yet done the upgrade, and you decide to remove the top skin as well be sure to order a new T 1204B flange for the tank. The skin holes are all pre-punched and it's very likely your flange hole pattern will not match up to the top skin. Ask me how I know.
Dick Seiders
 
Sorry, I should have mentioned that I burn almost 100% premium auto fuel. I did use 100ll p[us Decalin two yrs ago during a trip to Oshkosh, but none since.
Dick Seiders
 
Me too, regarding residue

I found the same residue on the bottom of my tank too. Only premium auto gas in my tank at this point and only 17 hours on the hobbs, so not many gallons through the system.

I'm curious to know more...

Slane
 
Typed in a post and lost it. basically what I said was based on what Slane saw in his tank with only 17 hrs on the engine and mine with the same thing at 240 hrs the premium auto fuel must have the gray matter in it's formulation. Probably the only reason more have not seen it is not many take the top skin off and so don't get the view. There you go. Probably we all have it and don't know it So it apparently not a problem , right? For one I would like to know what it is. Are there any chem-people in the forum who could provide some intelligence on this? After all if we all have it there must be some additional curiousity out there.
Dick Seiders
 
Could the residue in the tank be a product of mogas storage in plastic 5-gallon containers? I have noticed that if I store mogas (Premium 91 auto gas) in red plastic 5-gallon containers for more than a couple of days, the fuel takes on a pinkish hue which may be a product of the fuel's (ethanol's?) interaction with the red plastic? Or, it may be some initial form of "phase separation"?
 
Last edited:
for the past 130 hrs i have burned only premium no lead auto gas.the aluminum wing tanks in my dakota hawk are only 6 gallons so i get a good look at their insides with a flashlight every time i add fuel.......the inside bottoms are spotless and shiny.
 
David, my gas cans are yellow and I see no tint after 4 years of use. Don't know what we are looking at, but doubt is bleed-off from the gas bottles. I am trying to get some assistance from Tony T. on posting a photo of the material in the tank to this thread. The only guess I have thus far is the gray stuff in it's dry form bears a resemblance color-wise to the fuzz I find each condition inspection on my gascolator screen. Another possibility is IF the ethanol is slowly degrading the tank sealant the residue could be very fine particles of the partially dissolved sealant. The gray color is a very close match to the sealant we use. I never had this material show up in my RV6A, but I also never had autogas with ethanol in the tanks. Interesting? I may contact Flamemaster and ask if they would like to analyze a sample of the powder recovered from the tank. Now THAT would be ineresting.
Note to Bob Noffs in the Dakota Hawk comment. Are your tanks sealed with the same material we are using on the RV12's? (Flamemaster 3204 class B2)
Thanks for any feedback.
Dick Seiders 120093
 
forgot to mention my mogas is ethanol free and i have no sealant in my tanks, they are welded.
so maybe the alcohol is reacting with something?
i guess the end point would be to have a sample analyzed which seems reasonable because at what point can this stuff cause a problem somewhere?
 
Weldable 5000 series aluminum alloy?

It would be nice if Van?s were to produce the RV-12?s fuel tank components from an aluminum alloy other than 2024-T3. Seems to me if the tank components were made of a 5000 series aluminum alloy that lends itself to being weldable, it would give the builder the option of welding up the tank components or using tank sealers if not wanting to pay a professional welder to weld the seams and rivet holes. But I?m not an engineer - there may be good reason this is not a good idea ? but on the surface it seems plausible.
 
I'd like to see a tank made of poly. It might be heavier, but I think it would be more resistant to leaks and rupture.
 
Heard from Tony today, and he will post the photo of the residue on Tuesday thank you Tony. I worked on tank again today, and after close inspection of the residue am convinced it's partially dissolved sealant. If so, I will likely be building/buying a new tank. Removing the sealant is not feasible. Why would it dissolve? Don't know. Maybe too old when applied. Maybe defective who knows? Maybe the ethanol is doing it? What I am fairly sure of is I don't want this material flowing thru my fuel system. Will call Van's tomorrow to get their expertise and opinion. By the way Tony told me his tank was free of any residue last time he had top skin off (300 hrs). Would be interested to hear if any of you have the problem, and if so we could share ideas to find a solution.
Dick Seiders
 
Hi Dick,

Just got home from the air races. Here is your photo of the fuel tank residue:

i-8SkWvvt-M.jpg
 
I am also just catching up on this SB and removed the tank top - same white/grey residue. I transport my auto fuel in Eagle U2-51-S Red Galvanized Steel Type II Gas Safety Cans.

For the first 2 years I was able to get ethanol free gas and never noticed the residue. When I could no longer get the ethanol free fuel, I had to switch to fuel with ethanol and started noticing the residue in the cans as well as in the Mr. Funnel that all of the fuel goes thru. I was hoping that all of the residue was being caught by the funnel, but apparently not.

Probably 100 hours since I started noticing it. No problems and I have not seen anything in the carb bowls.

Sure would like to know what it is and potential issues it may cause, if any.
 
if you see it in the funnel and also in the canisters then it does not seem to be related to the sealant dissolving but rather something contained in the original fuel from the gas station.
 
I have not seen the material in the funnels, plastic bottles or anything else until I pulled the top skin off to do the latest mod when I saw it in the tank. I have ordered carb gaskets so I can check the carb bowls altho I do not expect to see it there. Reason? It has been collected in my gascolator screen. Saw it last few years and concluded it was junk that was filtered out of the gas. It was there again this inspection, and I believe the gascolator is doing an effective filtering job. There was enough of it this year that I ordered a new screen. I have not yet had a problem with the fuel, and I hope that continues. Maybe the material flows thru the engine fuel system and burns up with the fuel? Somehow that doesn't seem like a good thing.
I don't know for certain what the material is , but it looks very much like finely dissolved tank sealant. Same color and the texture (could be ) is what would be produced if the ethanol is slowly working on the sealant.
I spoke with a tech person at Flamemaster which produces our sealant and he said simply that the sealant we use is designed for jp3, jp4, and aviation fuel, not car gas. He asked how long I have been using the car gas ( 4 years) and his response was that I should remove all the sealant and replace it with a fresh application. as it is apparently eroding.
I don't intend to do that and then again every few years thereafter. I have contracted with a fabrication shop to duplicate the tank dimensions in a 5032 welded construction tank. The obvious goal is to have a tank with little to no tank sealant to avoid the ethanol solvent issue. If someone out there has a better idea I would appreciate hearing about it, but as of now I am pressing on with this plan. Thanks.
Dick Seiders
 
Personally I will only use PPG (PRC-Desoto) sealant in tanks, not a fan of the flamemaster brand, old habits die hard.
 
Dick,

I, for one, would be very interested to hear about your progress with the welded tank. Please keep us posted. As for the Flamemaster sealant being formulated for jet fuel and avgas only, some input from the Van's folks would be very helpful. Scott????

Alex
 
Alex, I agree, but tried calling Van's several times and could not find anyone to talk to.(Primer wars apparently) First time that ever happened I must admit, but decided to move on anyway. The thread has been on post for 10 days and has attracted no interest from Van's (Scott) much to my disappointment. Sooner or later we have to make our own decisions.
Dick Seiders
 
Dick,
Here is a picture of the inside of my tank taken in May. I use Shell premium with ethanol or Chevron Premium with ethanol pretty much exclusively unless I am away from home base. The tank is shiny clean inside at 250 hours.
i-PthbVGX-L.jpg


The speculation has been all about ethanol but no mention of has been made about the detergent packages that auto fuels contain. These vary by gasoline brand and could be more active to sealant than ethanol. Just a thought.
 

Dick,

I, for one, would be very interested to hear about your progress with the welded tank. Please keep us posted. As for the Flamemaster sealant being formulated for jet fuel and avgas only, some input from the Van's folks would be very helpful. Scott????

Alex

Within the above linked SB document there is the following text...

We have not yet seen any effect of E10 ethanol on the RV-12 tanks in service. But it is mentioned here so RV-12 owners pay
attention to the tank sealant during inspections, especially if ethanol separation is likely to have occurred.


N412RV, the red RV-12 prototype is now 6.5 years old and has 1235+ hours.
The above statement is still valid.
The airplane is still flying with the original fuel tank and has been operated predominately on E10 auto fuel. Because of our commercial type of operations, it gets extensive inspections every 100 hrs. There has been no indications of any problems with the fuel tank sealant.
 
Alex, I agree, but tried calling Van's several times and could not find anyone to talk to.(Primer wars apparently) First time that ever happened I must admit, but decided to move on anyway. The thread has been on post for 10 days and has attracted no interest from Van's (Scott) much to my disappointment. Sooner or later we have to make our own decisions.
Dick Seiders

Dick,
Please see my other post (#24).
I didn't post because I didn't have anything of value to add.
I have seen no problem.
As already mentioned, there are a lot of different factors that could be having an influence on the coating seen in tanks. Without testing, it would be incorrect to just assume it was fuel effecting the sealant (as Tony has already pointed out). It would also be incorrect to assume it is a problem... I.E., might just be related to different fuel suppliers, and of no effect on engine/systems operation or longevity.

Good luck with the welded tank. Experience shows that a leak free welded tank is not a simple slam dunk project. Please post to the forum an update on how it turns out.
 
Tony, your tank looks great. Maybe I should ask you to build one for me. It's clear from your picture that I used a lot more tank sealant than you did. Maybe that's part of my problem. However, I am on a new path now and I will see it thru to completion. I must admit I am excited about having a tank essentially free of sealant, and rivets.
Scott, thanks for the point of view and the facts on long use w/o issue. It just wasn't in my case. I have had ideas about the tank design for some time now and feel I am headed in the right direction. I will certainly keep the thread current with the new tank story as it progresses.
Dick Seiders
 
Tony, your tank looks great. Maybe I should ask you to build one for me. It's clear from your picture that I used a lot more tank sealant than you did. Maybe that's part of my problem. However, I am on a new path now and I will see it thru to completion. I must admit I am excited about having a tank essentially free of sealant, and rivets.
Scott, thanks for the point of view and the facts on long use w/o issue. It just wasn't in my case. I have had ideas about the tank design for some time now and feel I am headed in the right direction. I will certainly keep the thread current with the new tank story as it progresses.
Dick Seiders
 
I'm also doing my tank mod and noted the light grey colored film inside the tank. I've used premium, ethanol free mogas exclusively. I currently have 100 hours time.

Walt Shipley
 
Walt, that is really interesting. No ethanol ,but still a gray film. Perhaps other additives in the gas such as injector cleaning agents? The only way we will ever know is to have a residue analysis performed. I am planning to do just that. Some are reporting no residue at all (Tony T.) I suppose there could be dirty/contaminated gas coming from the supplier as well.
Dick Seiders
 
Walt, that is really interesting. No ethanol ,but still a gray film. Perhaps other additives in the gas such as injector cleaning agents? The only way we will ever know is to have a residue analysis performed. I am planning to do just that. Some are reporting no residue at all (Tony T.) I suppose there could be dirty/contaminated gas coming from the supplier as well.
Dick Seiders

That's what I wanted to read! All the info about this issue is based on only a few anecdotal incidents. Lacking data derived from a valid sample size, even the best guesses are still just that. As mentioned, it may not be tank sealant at all, since presence of the contaminant hasn't evidenced a direct link to the presence of ethanol. Good call on your part, Dick. I for one am anxiously waiting to know the results of a spec-an.
 
Apart from the residue is there any evidence that the sealant is softening or breaking down? If it was you'd expect to be able to scrape the surface away fairly easily. Don't think this has been mentioned anywhere.
 
Our condition inspection is upcoming and the tank SB is on the list. Looking at pulling the top of the tank off and going at it that way. For those who went this route, does the sending unit cover also need to be removed? How much sealant will be needed to put it all back together includng the new mechanical float gauge install.

Thanks.
 
The sending unit cover doesn't need to be removed. The 3.5 oz sealant cartridge was just enough to do the tank top and mods with a little left over.
 
While I was prepping for mod 2 and before I discovered the residue mentioned earlier I was going to order two or three of the small packets of sealant until I was advised by Van's parts person that for a few dollars more I could have a quart. Bought the quart so I now have plenty. Especially in view of fact it is my aim to use none on the welded tank. Anyone interested in the quart make an offer.
Regarding the sealant in the tank it does not peel, or rub off. It looks normal. I have decided to not have the powdery residue analyzed. Cost is a factor, and frankly I am convinced it is simply partially dissolved sealant. The residue is deposited on the bottom of my tank and can easily be removed by rubbing it with a rag, or your finger. It is the same in color, appearance, and feel as the sealant. There is nothing coming into the tank other than gasoline which unfortunately contains 10% ethanol. Whatever of the residue that flowed out to the the gascolator was trapped in the screen. The carb bowls are clean. I believe Van's SB on ethanol says it all. Read the words as well as between the lines and you conclude that it's a shame we have to use this ethanol tainted fuel. but there it is and we are being advised that it could be a problem. I have never experienced any separation of water from the alcohol into the fuel as the fuel is consumed on a very regular basis. The fuel remains in my tank at best two weeks, and most of the time less than that.

I called Flamemaster (sealant producer) today to again discuss my experience and received this from tech:
If you are burning car gas with ethanol for four years you need to remove all the old sealant (I think that is nearly impossible) and re seal with new sealant material to avoid the problem you describe. If he is right it makes more sense to put in a new tank.

I don't know if it is a problem down the line or not. What I do know is I have experienced one with my otherwise near perfect airplane so I am in the process of a tank change.
Dick Seiders
 
Dick, if you will recall, I posted several days ago that I had residue in my tank, and I have used non ethanol mogas exclusively in my plane. So, if it's the tank sealant breaking down, it's caused by something in the gasoline other than ethanol.

Walt
 
Good food for thought Walt. What we don't know yet is if the residue in your tank is what is in mine. There may be effects from other additives in the fuel that is causing the problem, or it may be those in addition to ethanol. Don't know. I did comment in the vent mod post my feedback from the sealant mfr. Perhaps one day I will find more of the same in my sealant free tank, but I seriously doubt that. Thanks for your feedback. Good luck and keep us posted on what you find to resolve your contamination issue.
Dick Seiders
 
I know this has been posted in the 12 thread, but we all use the same fuel tank sealant. I am troubled by the sealant manufacture saying if you use fuel with ethanol you need to replace the sealant after a certain time. The thought of rebuilding my tanks does not thrill me at all.

Thanks for the heads up.
 
Back
Top