View Full Version : Refueling trailer fuel quality question

18th Apr 2005, 03:21
I have a 300 gallon refueling trailer used to remote fuel my helicopter with 100LL Avgas. I've been operating from airport for the past 5 months so have not refueled from the trailer during that period. I keep the trailer slightly tilted toward lower draincock. I just drained about a pint into a glass jar to check quality and found it to be pristine clear blue, no visible water and a few black pieces of sediment.

I set the pint (with no cap) on a potting bench near the driveway, in full sunlight, intending to transfer it to my mower. I left it there for a couple or more hours and and came back to find it to be a cloudy greenish colour with a thick clumpy yellowish suspension at the bottom.

I'm not pumping into my copter until I know what the heck that was all about. Is it just the sunlight breaking it down in the clear glass jar or indicitive of something more sinister going on in that tank (presence of water, mold, chemical breakdown)?

It drained and appeared fine until I left that clear jar in the bright hot sun. Anyone know what happened? Is five months too long to keep the fuel?

Tony Chambers
18th Apr 2005, 11:14
Carryout a pump through and recirculate the fuel in the fuel bowser and then take another jar for testing. If the same happens clean your bowser, but if in doubt don't use the fuel. Better safe than sorry in my opinion.

18th Apr 2005, 12:43
Yes, I agree. If you don't want the fuel, let me know and I'll be happy to dispose of it free of charge through my competition car's engine, which is fine as it is an old engine with out a cat convertor, just to ensure it's done in a safe manner.. ;)

18th Apr 2005, 13:02
Info Link (Chevron) (http://www.chevron.com/prodserv/fuels/bulletin/longterm_gasoline/)

Hope this helps!

18th Apr 2005, 18:12
I have noticed that small amounts of avgas in pots goes green - and it happens with new avgas too. I use the stuff from my sampling pot in my mower. Incidently, I don't leave the delivery pipe full of fuel as it seems to go green in the pipe if left for a few weeks. On the basis of this I dont think you have a problem with the fuel in your bowser.

I take the view that if its blue and crystal clear out of the pump, Ill burn it in the aircraft. The stuff I have now is about 9 months old, and it still looks good.

I don't know if its light, evaporation or oxidation that makes it green but I suspect it is the loss of some volatile componant.
Try the same experiment with a sealed vessel if you are that bothered.

18th Apr 2005, 18:24
Danger, Danger,

what you have is plain old.. H2o,

the tank you have is it insulated?, if not then you will always have a moisture content that is really only seeable once the juice is oldish, the tank should have one of those big fuel filters after your pump, that will take out most of the moisture and slowly expand so as to stop you pumping anything with a high moisture content in it , then you are forced to change the thing, and clean out your tank.

I have refurbed a lot of trailer Bowsers and find they all suffer from moisture if they are not insulated, in fact I picked up a 320gall tank one day to be told its half full and we cant pump anything out!, reason Filter totally blocked by swelling due to moisture, so contents pumped out and into a new couple of barrels to see what its was,... oh it was half full alrightl , but made up of roughly 120 galls of water with about 50 gals of Avgas,, possibly the mans Jet R could have had some new sort of H2o burning turb..

Any uninsulated tank will make a suprising amount of moisture, even though the lid may never be opend for long, its pure physics, fuel gets warm in daytime, tank gets cold at night, your fuel then starts to float on the unseen peril of the sky.

Insulate or Die, or scrap your Bowser and get a new one, insulated and fully bunded so as to be within the new rules!


18th Apr 2005, 19:39
Following a rotors running pick up of Jet A1 at another operators base some years ago my trusty 206L1 settled gently to the ground from the low hover, whilst I was pre-occupied with idly wondering why the TOT was down around 320 C. The engine continued running on the ground.

I, and the ashen-faced refueller, took samples from both aircraft and bowser. Sure enough they were both quote "pristine clear blue, no visible water and a few black pieces of sediment". This is because they were both pure water!

Quite surprising how much a jar of water that's been living in a bowser smells of fuel. Beware.

18th Apr 2005, 19:53
Agreed, you can't be too careful with fuel.

Both my bowser and storage tank are stainless and insulated and I have a Flightline Supplies big black filter in the delivery line. The filter drain is always blue avgas and I check the filter element a couple of times a year. It still looks OK.

Thats probably why my fuel stays blue.



I have just had a delivery TODAY of fresh avgas into an empty bowser. Ill do the experiment of leaving two samples, one old and one new, open in a jar to see if it goes green. Ill post the results here in a day or two. Watch this space. (I might not be able to do the sun bit cos it constantly pisses down here:* )

19th Apr 2005, 02:51
Much to consider. This has been illuminating discussion.

I drained the original sample from the "dump valve" on the bottom of the tank (unfiltered). I'll try to recreate same with a sample through the filter and the nozzle. I'll also test for suspended H2O.

Gaseous - Keeping an eye out for the results of your experiment. Thanks!

19th Apr 2005, 03:53
That link that Flingwing pointed to has this sub-page, which is my guess as to what was happening:

"Microbial activity tends to concentrate at the gasoline-water interface. Moderate activity may cause the gasoline to lose brightness and clarity. Severe activity may stabilize gasoline-water emulsions and contaminate the fuel with visible particles of microbial sludge (biomass). Anaerobic microbial activity may generate hydrogen sulfide, giving the gasoline a "rotten egg" odor."

Moisture is present in every temperature change, where the tank vents breath in moist air, and cool conditions can condense it. The quote says "emulsion" as in a colloidal suspension of water and gas. The sunlight could have made some tiny airborne algae particles happy guys for a while. Modern anti-polution fuels get biological growth more easily, and biocides are recommended.

If it is suspended water with biological contamination (could there be a simple test for it?) the fuel is gone. Good for bonfires and the like.

19th Apr 2005, 08:13
Gin clear skies up here in Lancashire today, so after all this talk of moisture in fuel and little guys living off it , try this with your wasted (moisture laden) Avgas, mix 50/50 with any diesel fuel for any oil burning vehicle, they really run well from it and cope with the water in suspension, however dont run on pure contam avgas, the old Derv engine then runs too hot on pure and tends to crack heads...! no prizes for how I found out!!

Way Way back I read a very interesting true " " story about the Microbal affects of contaminated Avgas on Navy Aircraft, it was only dicovered that Microbes would live in fuel after several unexplained ditchings, then one hero pilot realised something wasnt quite right and managed to get his A/c( Fairy Gannett) back to the carrier, the rest as they say is History

Also the sluge that is left after the tank is empty is sticky and slimmey, it can only be removed from most tanks by the liberal application of plenty of high pressure steam or nearly steaming water, then ati microbal spray and a good drying, but after steam has been used the latent heat normally dries it all perfectly, cant you tell who operates the dishwasher in my wifes house!!

Peter RB

19th Apr 2005, 23:54
I'll pick up the bowser tomorrow (Wednesday) and do the test.

Meanwhile I found out that oxidation causes precipitation and loss of clarity but I have not found over what time scale

I also saw a reference to sunlight affecting the dye but it wasnt too specific.I have lost the URL to that and cant find it again.

Edit: Found it

Digging in Flingwings chevron link, I found this.

Instability of avgas during storage is generally not a problem because of the way the fuel is manufactured, and most fuel is used within a few months of its manufacture. Storage stability can be an issue at locations where fuel is stored for occasional or emergency use. Avgas that has been properly manufactured, stored, and handled should remain stable for at least one year. Avgas subjected to longer storage or to improper storage or handling should be tested to be sure it meets all applicable specification requirements before use.

Full text at:

Microbial contamination in avgas is much less common than with jet fuel, although it does occur. Presumably, the lower occurrence in avgas is due to the toxicity of tetraethyl lead.

full text at

Both pages worth reading if you store avgas

20th Apr 2005, 08:13
Storage of 100LL was once explained to me to be for a maximum of three months, after that it was said to start to lose its ability to "Bang" to specification , I seem to think this was from the Fuel servers at EGNH, when we purchased quantities for motor racing and bike racing, but I wasnt really listening that hard so what Ive just written could be a complete load of junk! :ooh:


20th Apr 2005, 22:35
Ok, I've got the fuel.

Both samples come direct from the wholesaler so haven't been hanging around at an airport. The new sample was delivered on Monday, the old in August 2004. The old sample has been stored in a sealed insulated tank until yesterday when it was pumped into the aircraft so is representitive of what I am burning. The sample was drawn from the gascolator.

It is immediately obvious that the new fuel is a much more intense blue. The old fuel is still blue but with a greenish tint (if you know what I mean??). Both samples are crystal clear (no turbidity). When (if) we get a sunny day I'll see what happens. Till then they stay dark and sealed.

(If its nice on Friday, Peter, you could maybe come over to be an independant scrutineer and then we could fly to Whitewell for lunch)

The picture gives an idea of the difference. Old sample on left.


21st Apr 2005, 02:58
Gaseous - mine was in a similar sized jar and left un-capped in direct sun at about 24C for 3-4 hrs. The clumpy precipiate at bottom will remix with the rest to a lightly cloudy green. I'd show you, but don't have a IMG host sight to use.

So the heat and UV breakdown something, but what and will it do same with fresh?

21st Apr 2005, 08:23

Looking at the grey mess above my pile of bricks I doubt if we'll ever see sun again this month, But yes, most defo, if the Current Bun doth come out I'll give you a ring, or verse vicer on my mob.


Um'm the antisipation of crispy battered fish and giant chips, or even Fish pie, is starting to make even the Grey stuff seem insignificant.

:ok: :ok:

22nd Apr 2005, 14:08
Cross eyed.

Test Complete.

The two jars were opened at 8.30 this morning. both were still clear. There is a reasonable amount of sunshine. By 1400, both samples turbid with white precipitation at the bottom of the jar. The old fuel is more cloudy than the new, but the new is not much better. There is an approximately equal amount of gunge in the bottom of each sample.

The old fuel is OK for burning as Vfrpilotpb and I have just flown to the pub and back on it.

My verdict. Sunlight , and being in an open pot causes degradation of avgas which leads to precipitation of an unknown solid. The age of the avgas is irrelevant as it happens with new avgas. I will try to post a photo later to show what has happened.

I stick by my original statement that if it runs blue and crystal clear from the bowser I will burn it.

What you do with yours is your decision.

Hope this helps


At 1700 they are both more cloudy. The level has dropped by about a third due to evaporation. both samples have a greenish tint.


23rd Apr 2005, 04:49

That's very helpful. Since my first sample was unfiltered, bottom of bowser stationary for 5 months, then placed open in high heat/sunlight, I got similiar but a bit more dramatic results. I ran a sample through from the nozzle (which is filtered) and got similar results to you in slightly cooler conditions and less sun. I think the heat/sunlight/evaporation is the reason, not likely microbial (more typical of Jet A and quite fragrant).

I've ran my weed trimmer, mower, and gas blower on the samples and did not have to autorotate any of them. However, I'm ordering a field test kit for water and microbials before I fly the fuel. I'm feeling much more optimistic that it will check out.

Thanks for all the input. Here are a couple more relevant websites I found along the way:



23rd Apr 2005, 05:41
Gaseous and Cross-eyed,

This is one great thread! You fellows posed a problem, discussed it, and then conducted some nicely done experiments to settle the issue. I think this thread and you guys deserve a round of applause!

Stopping by pprune is never dull, always fun and always enlightening. Thanks!

23rd Apr 2005, 13:00
Thanks Nick,
praise indeed.

Final update on the experiment.
I got the camera out to photograph what is left only to find that both samples have gone! evaporated totally, leaving just pale blue powder in the bottom of the jars - in a little over 24 hours!!

It has been fairly sunny and warm for Lancashire- but by no means hot.

Volatility and control of evaporation is obviously a major issue for correct storage. We all know about the water issue but this was a new one to me. As a result of this I am going to paint my storage tank reflective silver rather than the dark brown it is to help keep the temperature down on sunny days. It could do with a repaint anyway.

I have learned quite a bit about avgas from this thread, mainly not to take it for granted that it will be OK, and it MUST be treated properly.

PPrune at its best is a great educational safety resource.
At its worst it drives me nuts!
I agree, its never dull and usually fun.


23rd Apr 2005, 23:11
Thanks, Nick. A fine compliment coming from you.

Flight school teaches basic pre-flight fuel inspection techniques but not fuel storage techniques. This exercise has been an eye-opener - at the very least taught me not to take the responsibility for granted. If you decide to own and operate your own bowser, you'd better learn all about fuel storage techniques (and fuel characteristics, fuel testing, fuel transportation, regulations, etc.).

25th Apr 2005, 08:10
I think we could do with some further "Farmyard Investigation" on this, Sunday just gone was a very good fine and sunny day with only a slight breeze where I live, I was doing the normal sorts of chores, washing the pots, vacuuming the carpets , feeding the tribe and mowing the lawn, so I thought "AH" I'll put some 95 octane petrol in a clean clear jar to see what happens.

4 hours later, 95 Octane all gone leaving only a very fine feel of oiliness, but none of the "White powder" observed in the sample I saw in the jar at the LZ adjacent to the home of Gaseous.

So question is, Is the White powder part of the Dye used in the Ident of 100LL, or is it some other sort of additive that is put there by the manufacturer when refining and mixing this Aviation Fuel, and if an additive what is it?

Peter R-B

25th Apr 2005, 18:27
Thanks Peter, The final piece of the puzzle just dropped in!
The precipitate is most likely Lead bromide - the stuff that makes your exhaust white. I evaporated some avgas in the dark and got no precipitate so the precipitation is caused by sunlight. What Avgas has got that 95 octane hasn't, and is photosensitive, is tetra ethyl lead and ethylene dibromide.

A little research yielded this: (URLs on machine at work so don't have them now)

Ethylene dibromide, a clear liquid, decomposes under the influence of light to form ethylene glycol and free bromide ions which are pretty reactive.

Tetra ethyl lead, another clear liquid, decomposes under light to give ethylene(I think) and free lead.

Lead atoms plus bromide ions react readily to produce lead bromide which is a white solid at normal temperature. This is the reaction that also happens in your combustion chamber where it does its magic. It then goes down your exhaust to make it white.

It seems sunlight is mimicing the conditions in the combustion chamber which activate the lead chemistry to give the precipitate in the fuel.
The identifier dye turns the white powder pale blue.

It doesn't happen with 95 octane as they use heavier benzene or its derivatives to increase the knock rating - ? the oily residue you got, Peter.

Any real chemists out there confirm this?

26th Apr 2005, 04:11
Here is a 15 minute sequence of pics that shows how quickly the dye begins to breakdown.

1) Fresh sample Avgas in open glass jar, sunlight 30C.:


2) By the time I returned from bowser with 2nd sample (4 mins.), the first had turned purple (they are now side buy side, 2nd sample on right:


3) Five minutes later, the 1st sample has returned to blue (though cloudy) and the 2nd sample is now purple:


I have no pic of the last where both are green with parcipitate in the bottom and eventually all liquid completely evaporated. It goes pretty quickly.

Thomas coupling
26th Apr 2005, 07:38
Doesn't anybody use water detection capsules?

We test the fuel every day with these, thought everyone did it?

Goes green if there is >3p.p.b.

26th Apr 2005, 08:07
Hey TC,

Real world, I have a V12 motor, dont you, Thought everybody had one,




26th Apr 2005, 10:13
Well, water detection tablets with the diddy syringe thing for the Jet A1 bowser, but a swill in a jar and a "Bright and Clear" check for the AVGAS.

I believe it's something to do with the lower tolerance for dissolved water in Jet A1 that the burners don't like, whereas a 1930's carburetor
and Champion's finest can still make a bang with a higher ppm of dissolved water.

The Shell man tests both fuels for water with his kit but as users we do as above. Should we be using tablets on the AVGAS?

Very interesting photos by the way. :ok:

26th Apr 2005, 14:22

Seems to be you wearing the White coat,..... so Ethelene Glycol was, and I think still is a liquid used as a coolant in big A/c piston engines....It was also injected along with water into the fuel stream of the Rolls Royce Griffon engine when at full throttle and full supercharged boost to give I believe more bang to the fuel.

Then, if it is present in the 100LL of today, is this done for the same reason to make a Low Lead fuel more explosive upon compression/ignition, seems the more we dig the wider the hole is appearing! but I am sure we are near the answer, despite the Farmyard Experiments!


26th Apr 2005, 18:47

Ethylene dibromide is present in avgas to scavenge the lead and prevent it fouling your plugs. Ethlene glycol is a product of photoinitiated decomposition and is not as far as I know a constituent of healthy avgas.

In the combustion chamber ethylene dibromide will decompose during the burn to hydrogen, carbon and bromide ions, it being too hot for ethylene glycol to exist, let alone form. The hydrogen and carbon then just burn with the rest.

Water is not miscible with healthy avgas to an extent that is problem. It separates out and can be drained off safely. Water will only mix if avgas is contaminated with surfactants. If water is left in avgas for a long time microbial growth is possible, but not likely due to fuel toxicity, at the water/fuel interface.

Summary of what I have learned about avgas form this thread.

Keep it clean, keep it dark and cool, keep the storage tank clean and preferably insulated. Drain off water and don't keep it for more than a year. Check it regularly. Filter it properly on the way to your aircraft. If its not clear and blue, or you are not sure about it, dont burn it in your aircraft.

Jack Plug
26th Apr 2005, 19:14
Cross eyed,
just a suggestion. if you resize your pictures to 800*600 or less before posting them we dont end up with threads that have to be scrolled horizontally.
it makes them easier to read.
good thread.

27th Apr 2005, 01:47
Jack Plug - I'm actually getting the hang of this pic posting stuff. Pics now resized for easier viewing. Thanks for the tip.

27th Jun 2012, 17:37
...as I found a batch of canisters, filled with Avgas by my predecessor.
That must have been well over two and a half years...

So I was 'googling' to see if there's any degradation of the fuel over time, keeping it in plastic canisters.
I found no info, so maybe someone can advice?

I'm also interested in the tenability (preservability?) of JET A1.

Thanks! :ok:


27th Jun 2012, 18:09
I seem to recall that Avgas should be laboratory tested after 3 months, and Jet fuel after 6 months.
This assumes that it has been un-touched for these periods, I.E. No new fuel has been added, and the fuel passes all the usual quality checks.

CAP748 Might have the correct information - I'm writing this from memory. Any aviation fuel supplier will be able to tell you of course.

Plastic containers are not the right material for storage btw, unless they have been designed for the purpose - which I doubt.


CAP748 Chapter 4, Para 1.3 (c):

"c) whenever laboratory testing is required e.g. when Jet A-1 has been stored and not added to for a period of six months or when aviation gasoline AVGAS has been stored and not added to for a period of three months."

28th Jun 2012, 11:28
Thanks TRC! :ok:

28th Jun 2012, 18:27
Water detection capsules are of more use for JET A than avgas as they are for detecting water in suspension. JET A is more likely to abscorb water than Avgas.

Water detection paste is better for avgas as you can check the botton of a container where water will lie.

Out of interest the CAA flight safety magazine Clued Up dropped on to the doormat this morning.

page 62 has a discussion on testing fuel and storage.