I am sitting in the hangar with my Piper Warrior II sitting outside. The battery is completely flat and the cabin smells like paint thinner. This is the first time that this has occurred and if anyone has experienced this before please let me know what is going on! This is a maintenance question and I am concerned leaving the plane in the current condition over night. This is NOT a 100LL smell.

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    $\begingroup$ I would not consider the smell of battery acid to be close to that of paint thinner, but very much an acid smell without the pungency of white vinegar. The only volatile fluid I can think of would be the compass fluid in the mag compass. $\endgroup$
    – J W
    Dec 21, 2016 at 23:52
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    $\begingroup$ For troubleshooting, the following would be helpful: local temperature conditions; hanger heated or not; frequency of aircraft use including when last used and by whom; any recent maintenance. $\endgroup$
    – J W
    Dec 21, 2016 at 23:55
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    $\begingroup$ For battery troubleshooting, I would start by checking battery condition, fluid level and connections, checking voltage across the battery, checking voltage at the master solenoid, and switch. $\endgroup$
    – J W
    Dec 21, 2016 at 23:58
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    $\begingroup$ Is there a logical reason for the battery being flat or are fuses/CB off? If not you may suspect it had an internal short circuit which heated the electrolyte and a reaction occurred, or there was a short circuit close to the battery (before any fuse/CB) and the odor is heated insulator. $\endgroup$
    – mins
    Dec 22, 2016 at 1:19
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    $\begingroup$ Just got a call back today. Battery was replaced under warranty. Still not sure why it was ran down to ~4 volts. Smell is 1000LL that had soaked into the cabin carpet around the fuel selector. Still no clue why battery was ran down and why fuel is leaking! Oh well, we will know more next week. $\endgroup$
    – Yogwhatup
    Dec 23, 2016 at 21:13

1 Answer 1


You've got two unrelated problems: The battery and the smell.

The Battery

Battery electrolyte doesn't really have a "smell" to it - at least not one you're going to notice in the cabin easily. If you open the cell caps on a newly-topped-off flooded battery and sniff you'll get a feeling for what the electrolyte smells like. If you have a sealed battery you're not going to smell electrolyte unless the battery completely loses its mind and vents a large quantity of electrolyte - you'd definitely notice the mess in the battery box if that happened. You may notice it in a conventional flooded-cell battery if the battery is overcharged (from high bus voltage, or from trying to charge a flat battery after jump-starting the plane), but again it's not going to be readily apparent in the cabin unless you've lost a large quantity of electrolyte or you're really boiling the battery from an over-charge.

If your battery's cells are full (or it's a sealed battery) and you didn't leave the master switch on then the likely cause of it being flat is that it's old and can't handle the low temperatures of winter anymore (or if it's a new battery it may have developed an internal fault and discharged itself).

If you left the master switch on putting the battery on a charger/conditioner overnight can usually bring it back to good operating condition. You can try that on a flat battery from an unknown cause too: The good charger/conditioners will warn you if they think the battery has an internal fault. If an overnight charge doesn't resolve the issue then you're going to need to replace the battery before further flight (and frankly replacing the battery is cheap insurance against getting stranded somewhere, so it merits consideration anyway).

The Smell

The smell of 100LL changes as it evaporates - lighter aromatic components vaporize faster, and will waft out of the cabin more quickly, leaving the smell from the heavier hydrocarbons lingering.
As you discovered avgas that's been evaporating for a while loses the characteristic benzene/toluene scent we're familiar with from sumping the tanks and has the general odor of turpentine/conventional mineral spirits ("paint thinner").

The first thing to check in the PA28 when you smell something like this in the cabin is the fuel selector valve, as it's a common failure point particularly in cold weather: The packing/tapered plug in the fuel selector valve has shrunk in the cold, and you're leaking fuel around the shaft (which is then soaking into the carpet and evaporating off, giving you the smell in the cabin). Other aircraft may have similar failure modes in their fuel selectors, but I'm a Piper guy so I can really only speak to their systems and associated quirks :-)

Since your shop identified the fuel selector as the problem it's an easy fix: Rebuild or replace the fuel valve and the leak will stop, probably for many years. (Piper Service Bulletin 355 is relevant to this issue for older Pipers - the O-ring identified in the exploded diagram dries out and shrinks/cracks, allowing avgas to leak around the shaft. There may be something similar in Piper's service documents for the Warrior II, I'm not sure if it uses the same internal valve or not)

Another common failure point would be the O-rings around the primer plunger in aircraft with a mechanical primer (anything before the Warrior III).
This doesn't normally manifest as a lingering smell in the cabin but rather a smell when you operate the primer plunger (usually also accompanied by the plunger being stiff/hard to operate). Much like the fuel selector it tends to manifest when the weather gets cold and things shrink or become brittle, and the cure is to disassemble and appropriately service the plunger mechanism (replace the O-rings and re-lube the mechanism with a fuel-safe lubricant).

  • $\begingroup$ voretaq7♦ I am forwarding this to my A&P now. This appears to be bang on with what is going on with my aircraft. The only unanswered question would be what is draining the battery! This was a new battery (only a few months old) and all electronics were switched off after my last flight (first thing I check in dead battery situations in all vehicles). Any suggestions on what to look for/probe out? $\endgroup$
    – Yogwhatup
    Dec 24, 2016 at 3:26
  • $\begingroup$ FOUND ISSUE(s). Battery was at four volts. We think it is a voltage leak most likely coming from the removable GPS mounted in the dash. The second issue was a fuel line fitting (one that connects to firewall) that was loose. Fuel was leaking from the firewall down to the carpet. Thank you everyone for your help. Hopefully this post will help others with similar issues. $\endgroup$
    – Yogwhatup
    Jan 17, 2017 at 20:41

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