[Chrysler300] New question on fuel tank sending units

["Bob Jasinski" <rpjasin@xxxxxxxxxxx>]

Since we're on the subject of fuel tank sending units, I thought I'd ask a
question that's been bugging me for years.  How is it that electric fuel
sending units are safe to use inside of a fuel tank?  Here we have a device
that has a voltage applied and conducts current through a sliding resistance
setup connected to a float.  It seems to me that it would be quite possible
for a spark to occur and ignite the gas vapors, yet I've never heard of that
happening.  What am I missing here?  Certainly there is oxygen within the
tank along with gas vapors, so the sending unit acting as the ignition
source could complete the fire triangle, but I've never heard of a problem,
even if the sending unit fails.  Any thoughts on this folks?
 
Bob J

  _____  

From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On
Behalf Of Rich Barber
Sent: Friday, December 28, 2007 12:37 PM
To: mwl1967@xxxxxxx; chrysler300@xxxxxxxxxxxxxxx
Subject: RE: [Chrysler300] How To Test? Fuel Sending Unit



For my 1955, I measured resistance of the removed sending unit at its
extremes-full and empty-float up and float down. Float down-around 75 Ohms,
float up-around 10 Ohms. Then I built a variable resistor from Radio Shack
parts, connected the variable resistor to the disconnected sender unit leads
in the trunk, adjusted the resistor to make the dash gauge read empty, 1/2
and full, measuring the resistance at each point. The values were similar,
so the sender was installed and sort of works. I have not chosen to make
multiple removals and installations to adjust the wire float to make sure
float down is truly empty. The variance in resistance as the float arm is
moved should be smooth to assure good contact of the slider on the
resistance wire.

I had my original sender rebuilt as it had a broken fine resistor wire. The
rebuilder installed a new resistor coil and slider, but they were of
different dimensions and it doesn't work very well. I seem to get a nervous
gas gauge needle, even when sitting still with the engine running. Possibly
due to voltage regulator variance.

So, the gauge sorta works, but I use the trip odometer as a primary
indicator of when its time to fill up. With all the cars I've owned and
driven, I've never seen any other than a 1961 Karmann Ghia VW that had a gas
gauge that was anywhere near accurate an linear throughout the range.
Irregular shaped tanks, crude design of senders and lack of a calibration
system preclude accurate remaining fuel indication. I hope the aircraft
industry does better with their fuel measuring systems and hope this helps
you.

Wishing all a Happy C-300'ly New Year
Rich Barber
1955 C-300 (had it out and about yesterday--to the tranny shop to evaluate
parts needs to stop minor leaks on the Powerflite. May need source of rear
seal and shift lever seal. Any good sources out there? I have the pan
gasket and replacement neutral switch. Noted an unused small bracket bolted
to the bottom on the driver's side. Perhaps to hold an illegal backup light
switch?)

-----Original Message-----
From: Chrysler300@ <mailto:Chrysler300%40yahoogroups.com> yahoogroups.com
[mailto:Chrysler300@ <mailto:Chrysler300%40yahoogroups.com> yahoogroups.com]
On
Behalf Of mwl1967@aol. <mailto:mwl1967%40aol.com> com
Sent: Friday, December 28, 2007 11:30 AM
To: chrysler300@ <mailto:chrysler300%40yahoogroups.com> yahoogroups.com
Subject: [Chrysler300] How To Test? Fuel Sending Unit

Can someone tell me what's the best way to test a sending unit without 
actually installing it in the car? Also, can/should the electrical
connections 
inside be cleaned or resoldered?

Thanks,
Mike Laiserin

K coupe painted and starting to look like a car again 

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