The International Cessna 170 Association

Has anyone experienced fuel 100LL darkening up in colour in one fuel tank only. I’ve notice now that if my aircraft sits for a few days 4-5 the fuel in my left tank when I check it has become very dark blue. Any thoughts?
Thanks
Mark

One event? Small sample?

One of my fuel sump valves occasionally drips just a little bit and should that happen, the fuel drips will evaporate as they "dangle" from the sump and the blue dye stays on/in the valve. It could be that you are seeing the same thing, and perhaps a true leak rather than a drip, enough that the first bolus of fuel in the tester is picking up the remaining concentrated dye and discoloring the fuel in your tester.

I thought the same so I increase the amount of fuel I pulled out of the tank with no change as well I rocked the aircraft to agitate the avgas in the tanks thinking it might mix the dye in with the fuel better, however no change. Now wondering if the fuel could be reacting with something in the tank? Thanks for the responses anyways.

Jetbush wrote:I thought the same so I increase the amount of fuel I pulled out of the tank with no change as well I rocked the aircraft to agitate the avgas in the tanks thinking it might mix the dye in with the fuel better, however no change. Now wondering if the fuel could be reacting with something in the tank? Thanks for the responses anyways.

Unlikely. The most likely reason is you got a “gulp” of heavily-dyed fuel sitting in the hose last time you re-fueled. Are you getting the heavy-dye from the tank you FIRST served when you last refueled?

I spent a lot of time (some time ago) trying to understand the specifics of avgas production/delivery. My original intent was to see if lead couldn’t be withheld from avgas until final delivery at the pump. For reasons I never understood I could not get answers from refiners as to WHY that could not be done...and I ultimately came to the conclusion they simply aren’t interested in changing the system in what they consider a low-priority/low-profit area of operations. (Why is it low profit considering the prices at the pump? See https://www.chevron.com/-/media/chevron ... review.pdf )

I do not know where in the refining process when/where the dye is injected or for positive if the dye used can precipitate out due to temperature changes, but that is something I suspect because I’ve seen deeply-colored fuel which was very cold and have never seen it in warm fuel. Not very scientific...I realize... but that’s what I’ve seen.

The tank with the darker coloured fuel is the tank which I refuel first, so you may be onto something. However I’m very consistent with my refueling procedures and this issues with the darker fuel has only occurred 3 times in the last 3 months. All same, thank you for your interest in my question.
Cheers
Mark

If you keep AVGAS long enough, it will loose all coloring. Takes about 7 years. It will still run well in your lawn mower.

Avgas has a much longer shelf-life than advertised (probably for liability reasons.). There’s a famous, if anecdotal, story about the beginnings of the CAF that was told to me by Lefty Gardner in-person at a cocktail party he hosted at his home following an air-show down at Harlingen. He said that they were buying surplus WW2 airplanes out of Davis-Monathans many thought for restoration and spare parts.... but the most-profitable parts they bought those airplanes for was the 20-year old aviation gasoline in the tanks! They were flying those airplanes out of storage with the fuel which had been sitting in them for years. They’d restore a few of them, salvage parts from them, and use the extra fuel in their crop-dusters.

We were invited with a group of friends to clean out a old hangar for aircraft bits and pieces before it was being demolished as the airfield had be closed for housing developments.when we arrived the bulldozers had already started their path of destruction. They were tearing down the hangars into a pile of broken wood and sheet steel and was going to burn it. [I know sheet steel doesn’t burn]. When on the bottom of the pile was a stainless steel drum about 45gals size. One of my sharp eyed friends stopped the bulldozer so he could pull it out. He stated “hey that would make a great fire pit if cut into half”. The drum was rolled out and found to be full of liquid . 5 of us managed to tip it up on its end and found it sealed .we open it up and decantered a small amount into a old glass jar found on site . The liquid was coloured a deep purple and smelled of Avgas.
5 five of us were standing around in a circle passing around this jar having a smell and giving a opinion. The dozer driver came up and asked us what was in the drum . “its avgas”. The look on his face was priceless and I will not repeat what he said . The drum was removed and contents were tested and found to be 115/145 purple avgas . The date on the drum was indicating it was 4 years old . The sad part of this is when the bon fire was lit ,people from around the area came to watch.

Foot note,
I received about 10 gallons of this liquid gold [purple] and placed it into one tank of my aeroplane . I took off on the other tank [100LL] and switched over to the 115/145 tank. I flew the aircraft on this tank until nearly dry . There wasn’t any difference what so ever in performance running on this higher octane. Nothing changed . Waste of time putting it in except I got it for free.

Small batches of 115/145 avgas is still produced on special order. Some of the air races require it. The purple color is derived from mixing the red and blue dyes.

If you keep AVGAS long enough,

Bruce, I still have 5 litres left of a twenty gallon batch, produced 22 years ago. Using it my lawnmower as you suggest. I’ve also used it in the past to start a fire. Burns but the whosh doesn’t have much thump to It, so now its 50% mix for the lawnmower. Its still blue.

I have noticed on a couple of occasions that 100LL placed in a clear, plastic bottle and exposed to sunlight will lose its blue color. Becomes clear. Still smells the same and will still run my tug.

I run 100LL in EVERYTHING that does not have a catalytic converter. One day I counted up the gasoline powered engines I own and came up with 21 total engines without catalytic converters that I have had for years.

With as little intermittent use as each engine gets, if I had been using mogas in those engines, I would be continuously rebuilding carbs and fuel systems. Since I use 100LL, I have never had to rebuild anything. 100LL just does not go bad.

I do try to replace the 100LL at least every year or two in each engine.

The only thing I would use mogas for, other than vehicles with catalytic converters, is wasp nests, weed control, and mixing it 25/75 with diesel to start fires when I burn brush piles.

170C wrote:I have noticed on a couple of occasions that 100LL placed in a clear, plastic bottle and exposed to sunlight will lose its blue color. Becomes clear. Still smells the same and will still run my tug.

You realize, Pokey, that the higher octane 100/130 has even MORE lead in it to make it burn s l o w e r (not detonate)... and that’s why they color it GREEN.