Additional gas gauges??

[tom geiger]

Once the weathers gets a bit better I am going to drop the tanks to get one of the sender units replaced. In doing this I was wondering if I can add
a couple led gas gauges in addition to the OEM gauge? Was hoping the additional gas gauges just read the level in just the tanks they’re assigned.

Just wondered if possible?
Thanks,
Tom
--
Tom Geiger
76 Eleganza II
KCMO

 

[Melbo]

Tom

The signal from the sending units goes to the tank selector switch ( I think ) and then from there to the gauge so if you were going to use two gauges
I would think that you would have to connect before the tank selector switch. I'm sure some people with much more experience will chime in if what I
said is wrong. I am speaking from my experience with my 73.

HTH

Melbo
--
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC

 

[Jim Hupy]

I never, never trust the stock gages. They both work as well as GMC gages
ever work. As long as gas can transfer freely back and forth between the
two tanks, they can never be trusted to tell you how much you have in
either tank. I just know how many miles I have traveled, and how many
gallons I have put into the tank. I use a estimated mileage of 8 mpg. Do
the math in my head. Drive 250 miles and fill it up. That is about 4-5
hours in the driver's seat.
The rocker switch on the dash is what switches the sender units, as well as
the fuel gage.
Jim Hupy
Salem, Oregon

On Sat, Feb 6, 2021, 4:47 PM melmull--- via Gmclist
wrote:

> Tom
>
> The signal from the sending units goes to the tank selector switch ( I
> think ) and then from there to the gauge so if you were going to use two
> gauges
> I would think that you would have to connect before the tank selector
> switch. I'm sure some people with much more experience will chime in if
> what I
> said is wrong. I am speaking from my experience with my 73.
>
> HTH
>
> Melbo
> --
> Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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>

 

[Ken H.]

Tom,

You can certainly try it, but I predict unsatisfactory results. If you
look at the wiring diagram, you'll see that the gauge is nothing but an
ohmmeter measuring the resistance of each 0-90 Ohm sending unit. That
means that the current flowing through each of them is what's being
indicated on the meter. When you add a meter in parallel with the OEM one,
the current through the sender will be increased and that through the OEM
meter will probably be changed -- how is unpredictable without knowing more
about the impedance of that meter. That's for the selected sender. The
unselected meter and sender should be accurate, dependent upon the
calibration of the meter.

I suppose you understand how the tanks are plumbed and the meter
consequently works, but I'm going to run through it for those who may not:
The two tanks are connected at approximately the 6 gallon level by the fill
tube running down the left side of the tanks. That means that until there
is 6 gallons left in the selected tank, and therefore the meter, there is
an equal volume of gasoline in each tank -- and the meter should read the
same regardless of the tank selector switch. Only when there's less than 12
total gallons of fuel left should the gauge reading depend upon the tank
selector position. Basically what you'll likely gain by adding two more
gauges is the continuous reading of each of the two 6 gallons "reserves".

Now if you're looking for more modern, perhaps more accurate, readouts, the
correct way, IMHO, is to merely replace the OEM gauge with one new one, in
the original wiring location -- controlled by the tank selector switch.
However, be aware going in that the probable cause of any inaccuracy you're
now seeing is most likely the OEM senders -- they're merely float/lever
operated wire-wound rheostats, which can become erratic after 40 years of
life even in a benign environment, not to mention the terrible one those
have been in.

HTH,

Ken H.

On Sat, Feb 6, 2021 at 7:34 PM tom geiger via Gmclist <

> Once the weathers gets a bit better I am going to drop the tanks to get
> one of the sender units replaced. In doing this I was wondering if I can
> add
> a couple led gas gauges in addition to the OEM gauge? Was hoping the
> additional gas gauges just read the level in just the tanks they’re
> assigned.
>
>
> Just wondered if possible?
> Thanks,
> Tom
> --
> Tom Geiger
> 76 Eleganza II
> KCMO
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[tom geiger]

Ok guys, no more gas gauges then. Fingers crossed on getting sending unit going and new selector valve in, when the weather permits.

Thanks,
TG
--
Tom Geiger
76 Eleganza II
KCMO

 

[john r. lebetski]

The gauge is same as any 90 Ohm GM setup except for the DPDT dash switch that is an A/B selector that also sends 12V to the valve when in AUX. In fact
my 1970 Buick GS uses the same 3 gauge cluster with slightly different font. A long proven design. The relatively shallow tanks linked by fill tube,
coupled with long sitting periods over winter and user misunderstanding of the system leads it to be bad rapped. When in working condition it works
as designed. When above the fill tube you are pulling from a 50 so needle drop is slow. Once below that you are pulling from a 25 so needle drop is
2 x.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[tom geiger]

Really interesting guys. Looks like there is no place for a upgrade here on the system. I’ll get things back in order and go with stock setup.

Thanks,
TG
--
Tom Geiger
76 Eleganza II
KCMO

 

[Matt Colie]

> Really interesting guys. Looks like there is no place for a upgrade here on the system. I’ll get things back in order and go with stock
> setup.
>
> Thanks,
> TG

Tom,

I took the time to repair my tank senders twice before I finally did a complete rebuild. I did this eight years ago. I never wrote this up because
the whole effort while it was successful, it was clearly a Pyrrhic victory. While the parts were not expensive, the effort was so great and involved
that I would have been better off to either buy new replacements or send them off to a rebuilder (that I have since lost track off) and have them do
about what I did but with experience. It is nice having working gages.

The GM sending units are supposed to be 0µ empty and 90µ full. (This is backwards from what makes sense. If something fails, it should go to Zero.)
In actual fact, they are all 3µ empty and ~87µ full. There are electronics available to supply very stable reference voltage that you could put
through a know resister and monitor the current and thereby the resistance (position) of the fuel sending unit. One would have to abandon the
existing fuel gage in the instrument panel as this could not be mixed with the existing system, but other than requiring a new wire to the connector
by the tank selector valve, most of the installation would be relatively simple. I thought about it, but once the panel was reporting reliably, I
lost interest.

When we travel, Mary is usually driving if it is daytime, we have not had an issue. She will switch to the auxiliary tank when the fuel is at half.
This way, if we end the driving day before we take on fuel again, we have fuel in the main tank for the APU if it is needed. As I write the Odo
number on each fuel slip and with the fill vent mod I can reliably fill to the same "full". That means that I can usually predict to the nearest
gallon how much fuel I will be able to take on at the next stop. Between GasBuddy and the now discontinued Street Atlas, I know how far and where
that will happen.

Matt

--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit