Why does avgas 100LL smell differently than automobile gasoline? And why don't avgas 100LL fumes from a fuel tester located in the cabin make pilots ill?

  • 1
    $\begingroup$ Why are you sniffing avgas? $\endgroup$
    – Vikki
    Commented Apr 5, 2019 at 2:51

1 Answer 1


The sweet smell of 100LL AvGas is due in large part—if not entirely—to the additive Tetraethyllead (TEL). TEL is included in the formulation of 100LL as an anti-detonation additive, octane booster, and lubricant.

A fuel tester stored in the aircraft cabin should not induce crew illness because the tester should be drained of all but residual fuel, that residual fuel will evaporate very quickly—usually long before startup, and aircraft cabins are typically well ventilated.

  • 3
    $\begingroup$ The core blendstock and additive packages for 100LL are also different than for automotive gasoline - I'm not 100% solid on the specific chemistry, but I know the hydrocarbon ratios are different, and I believe there's no oxegenating agent (MTBE/ETBE) in avgas, or it's present at a much lower ratio than in conventional automotive gasoline (and obviously ethanol as an oxegenating agent is a no-go as it's incompatible with most aviation fuel systems, and that's a noticeable part of the familiar "(automotive) gasoline" smell most of us know). $\endgroup$
    – voretaq7
    Commented Dec 23, 2016 at 22:37
  • $\begingroup$ Yes, I was using that term in its non-aviation sense for generic motor vehicle fuels (I've modified my comment to be more specific since I wasn't quite at the maximum character limit for a comment :-) $\endgroup$
    – voretaq7
    Commented Dec 23, 2016 at 23:21
  • $\begingroup$ @voretaq7 Roger. Comment deleted as obsolete $\endgroup$
    – J W
    Commented Dec 23, 2016 at 23:45

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