Should you use fuel that’s been stored for years? A lawyer would say no. What does our expert say?

I received a note from Gerd Wengler who flies a Turbo Skylane with a Lycoming TIO-540 engine. He and his wife plan to fly up to the Arctic this summer and were concerned about the fuel supply.

I received a note from Gerd Wengler who flies a Turbo Skylane with a Lycoming TIO-540 engine. He and his wife plan to fly up to the Arctic this summer and were concerned about the fuel supply.

“”I have the opportunity to buy a drum of 100LL at a remote community, however it is several years old,”" he says. “”According to the fuel distributor, the drums are stored properly and are sealed.”"

He asks if there is a quick way to check the fuel to ensure that it is on spec and OK to use. He had heard rumors that if the fuel is still blue and clear it will be fine.

Unfortunately there is no easy answer to this question. The generally accepted industry standard is that under normal conditions, 100LL will meet the requirements of the ASTM D-910 specification up to one year after production.

That said, let’s look at what can go wrong with fuel after extended storage. The most common problem is moisture. This is where the clear and bright standard comes in. If the sample has a significant amount of water entrapped in it, it will be hazy or kind of milky. If you let the sample set and the water settles out, the fuel should be OK if you are very careful about how the fuel is transferred and the water drains are checked often and correctly.

One of the problems with some Cessnas is that they can get a rippled bottom in the fuel tank. These ripples can hold a significant amount of water that is not drained out during the sumping process when the plane is sitting still. Then when the plane is flown, the water can be dislodged from the ripples and end up in the carb.

The other problem with extended fuel storage is that fuel can oxidize over time. This is less of an issue in colder climates, however over time all fuel will tend to oxidize and form gums. This gum can cause problems in fuel filters and carburetors.

Unfortunately there is not a good test for gum that can be run in the field. In the past, we told people to smell the fuel, but that is against OSHA recommendations.

Since Mr. Wengler will be outside the USA, he may wish to check the fuel for a gum-type odor. By now you are all asking, “”What is a gum-type odor?”" If any of you have worked on an old carburetor that has been sitting for years, you will know what gum smells like.

The smell check is not fool proof. For example, fuels from different refineries sometimes have different smells. Also, by the time a fuel sample has a gum-type smell, it can be plugging up your filter or carb. Unfortunately, an oxidized fuel will plug up your fuel system well before it plugs up a fuel filter in, say, a funnel or similar device. It is important to note that auto gas, and especially auto gas with two-cycle oil mixed in, will form gums much quicker than 100LL.

I have checked some samples of 100LL after being in storage for more than five years and they were on spec. These samples were all stored properly with no moisture or high temperature exposure. In the samples, there was a small amount of lead settling so that the octane of the fuel pulled off the top was down a few numbers compared to the fuel taken off the bottom. However, I stirred the sample for a few minutes and the octanes were then equal and the fuel met all requirements.

So should he use the fuel? Well, a lawyer would say no. But I know that people have been using fuel stored in colder climates for many years without a problem. So roll the drum around a little and then pull a sample. If it is clear, blue and bright, with no signs of moisture and smells normal, then it is probably OK.

Understand that I said probably and not definitely. There is some risk associated with using this fuel, so be very careful and do not just assume that it is good.

Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at

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