Fuel Level circuit in gas tank - Dangerous? - Put my mind at ease please.

[ncpetersc]

I know this is silly, as this is probably done in millions of vehicles without issue. But I can't stop thinking about the fact that part of an electrical circuit is in the gas tank. Why isn't this dangerous?

My understanding is that fuel level is basically sensed using a potentiometer which exhibits a different resistance based on float arm angle.

I'm only assuming that this is must be part of an electrical circuit to be measured. And an electrical circuit failure could result in an arc, causing disastrous results.

I know this concern has to be completely ridiculous. But I would love it if someone could put my mind at ease with some nice logical explanation as to why this isn't something to worry about.

I'm about to install a new tank (and sending unit) and for some reason can't stop thinking about this today.

Thanks!

[Steeveedee]

Generally speaking, the inside of the tank will be filled with fuel and fuel vapors. That combination doesn't allow for a lot of air and/or oxygen, so the tank will be above the upper explosive limit of fuel and air. I've never heard of a fire inside a fuel tank in a truck. If it gets hit and punctured and a source of ignition is present, yes. But that is a rare scenario.

[Just Yourshadow]

You're not send 12v into the gas tank unless you have an electric fuel pump in there. The fuel sender is designed to vary the resistance to ground based on the level.

[AussieinNC]

The gauge measures the resistance of that rheostat, and it applies a VERY minimal voltage to do it. ~5v DC which is nowhere close to enough to cause a spark.

Even if it does spark, there would be an almost zero chance of starting a fire.

If you have any fuel in the tank, the vapor concentration is far past what you can ignite. (gasoline doesn't burn at all. gasoline vapors burn, and it has to be between 1 and 7% vapor to air. Any more or less and it won't do a thing)

The only time you would get that low of a concentration of vapor in the tank is if it is absolutely empty, in which case you aren't moving the sender anyway.

Hope this helps...

[cornerstone]

Originally Posted by AussieinNC

(gasoline doesn't burn at all. gasoline vapors burn, and it has to be between 1 and 7% vapor to air. Any more or less and it won't do a thing)

This is what settles my wandering mind the best as I have considered this as well. Think of this... can you spark a match under water? well ... you probably can but the point is that the water itself won't burn.

[Rufas]

I can't think of any modern vehicle that doesn't use this setup. It's been this way for almost 90 to 100 years. Your daily driver uses this same setup.

Don't loose sleep over it...

[davepl]

I understand the concern. There's a wire going into a chamber of potentially atomized air and fuel. One spark == big boom and yet we don't see it on the news!

I imagine there is a LOT of resistance in the gauge itself, so that the amount of current the brown sender wire is carrying to ground is very low.

[Steeveedee]

In addition to what I said previously- hundreds of millions of vehicles use this setup, with no danger.

[terry b]

Wow!!

[ncpetersc]

Yeah, I knew it was a dumb question due to it being in EVERY vehicle, and really even more concerning now with in tank fuel pumps and such.

I didn't know about the vapor concentration and lack of oxygen makes sense. I just needed to understand something logical that would help me understand. Thank you all.

[mike16]

Ka-boom!

[dmjlambert]

Well mike16 blew up, but everybody else is still ok right? Poor ol' mike...

[AussieinNC]

That AZ heat may have gotten to him....

"But its a dry heat!"