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71 Eldo: Fuel gauge lesson

Started by wbdeford, August 09, 2015, 04:45:50 PM

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wbdeford

With every old car I have owned to date, when the ignition switch is off, the fuel gauge reads Empty.   Many cars also show Full or near Full for a long time, before dropping rapidly in the last 1/2 tank.  So, my gauge was registering above half for a while and I thought nothing of it--paid no attention to it when the key was off.  Oil light and Water Temp light were not working, so I figured it was a fuse but was lazy about fixing it.

Today, I started to wonder about the fuel gauge.  It not only still registered higher than I thought, but did not seem to have moved at all....I found the blown fuse, removed it, and connected remote starter switch between the fuse terminals.  Turn ignition key on, push the remote starter switch, and sure enough--Oil light comes on, and fuel gauge drops precipitously to 1/4 tank.

Lesson learned....
1958 Sedan de Ville

Past:
1956 Fleetwood 75 Sedan
1957 Fleetwood 60 Special
1958 Miller-Meteor Futura Landau Duplex
1960 Coupe de Ville
1966 De Ville Convertible
1970 De Ville Convertible
1971 Eldorado Convertible
1979 Sedan de Ville
1980 Seville

"Cadillac Kid" Greg Surfas 15364

William,
That's why when one thing quits working (oil light, etc.) it is wise to find and correct the problem. Usually, however when the instrument fuse blows and there is no power to the fuel guage, it tends to hug "empty".

Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

wbdeford

Quote from: "Cadillac Kid"  Greg Surfas 15364 on August 09, 2015, 05:08:15 PM
William,
That's why when one thing quits working (oil light, etc.) it is wise to find and correct the problem. Usually, however when the instrument fuse blows and there is no power to the fuel guage, it tends to hug "empty".

Greg Surfas

Right.  New fuse is in now and doesn't blow--so far.
1958 Sedan de Ville

Past:
1956 Fleetwood 75 Sedan
1957 Fleetwood 60 Special
1958 Miller-Meteor Futura Landau Duplex
1960 Coupe de Ville
1966 De Ville Convertible
1970 De Ville Convertible
1971 Eldorado Convertible
1979 Sedan de Ville
1980 Seville

TJ Hopland

My 73's gas gauge starts out on E for about the first 5 mins then pops to where it should be and is fine the rest of the day.  Does not seem to matter if I drive or if its just warming up in the driveway.   Have not tried just turning the key on.   It seems to do it worse when the tank is lower.   I don't notice it as often when its full.    Its been doing that for maybe 10 years now and I keep thinking I should figure it out before it quits working on me some day. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

mgbeda

I have a '75 Buick (sorry) and the gas gauge in that always stays where it left off when the key is off.  Otherwise it works normally.  it's been like this since 1980, at least.  I always thought it was a feature, but maybe it's a bug.

-mB
-Mike Beda
CLC #24610
1976 Sedan DeVille (Bessie)

Marcel75

#5
Hi Mike,

I'd bet no bug for you. The Cadillac 1970 users manual underline that the needle of the gauge is of "balanced type" (I don't know the meaning of that...) and may stay anywhere between E and F on turning off key. This is the case on my 70 Eldorado.

Marcel

mgbeda

Interesting about the '70 gas gauge.  By '76 it had changed to an "E when power is off" type, like most cars.  I wonder why, as I think it's a nice convenience to be able to check the gas level with the car off.

-mB
-Mike Beda
CLC #24610
1976 Sedan DeVille (Bessie)

Scot Minesinger

My 1970 goes to empty when car is turned off, then after it starts gas gauge provides the correct reading.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Glen

Quote from: mgbeda on August 14, 2015, 03:02:48 PM
I think it's a nice convenience to be able to check the gas level with the car off.

-mB

Convenient for the gas thief to.  He just needs to look at your gauge to see if you have a enough gas to be worth siphoning. 

Glen Houlton CLC #727 
CLCMRC benefactor #104

TJ Hopland

I think earlier fuel gauges had a dual coil setup .  One coil was basically always powered when the key was on and the other was the one that got the variable signal from the tank.   I think part of the dual coil thing was to make it less sensitive to voltage changes.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

bcroe

Quote from: TJ Hopland on August 15, 2015, 09:13:59 AM
I think earlier fuel gauges had a dual coil setup .  One coil was basically always powered when the key was on and the other was the one that got the variable signal from the tank.   I think part of the dual coil thing was to make it less sensitive to voltage changes. 

Agreed.  Probably the later are cheaper, and with a high capacity alternator, voltage regulation
is less of a problem.  Truth is, there were situations where that limited output generator was
leaving you in discharge, esp at idle and with lots of stuff turned on.  Bruce Roe