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Bouncy Fuel Gauge

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Naomi

Jedi Hopeful
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The fuel gauge on my 64 bounces all over the place and ya can only tell how much gas you actually have if the car is sitting still or on a straight stretch. I wanted to buy one of the "steady ones" like on my 80 B but the hubby says it won't work because of some "ohm difference (his words).
Is he just trying to get out of working on the 64 or is he telling me the truth?

Your turn,


Naomi -- Owner of a 64 MGB & an 80 MGB. Both repaireded over 4000 times but still loved /ubbthreads/images/graemlins/smile.gif <font color="purple"> </font>
 
Sounds like there are no baffles in the tank and when the fuel sloshes around it moves the float on the sending unit up and down.
 
It was like that with the old tank and two years ago we put a new one in. Purchased from Moss but of course that doesn't mean it has baffles. The hubby swears to me that 62-65 MGB used a different fuel gauge. Sure looks the same to me as the 80 /ubbthreads/images/graemlins/smile.gif


Naomi -- Owner of a 1964 MGB & a 1980 MGB. Both repaired over 4000 times and still loved /ubbthreads/images/graemlins/smile.gif
 
Na - different fuel guage, he's right (hate to side with him, hehehe)...your new fuel tank doesn't have baffles either....however, my early cars guages don't bounce around like that....it might just be a bad guage..if you want, I'll send you another to check yours with....you can send it back if it doesn't correct your problem
 
Say it ain't true Tony --- he can't be right -- I'll never live it down /ubbthreads/images/graemlins/frown.gif


Naomi -- Owner of a 1964 MGB & a 1980 MGB. Both repaired over 4000 times and still loved
 
Hey, why is my signature messing up?



Naomi -- Owner of a 1964 MGB & a 1980 MGB. Both repaired over 4000 times and still loved
 
Naomi, check and make sure the connections at both the gauge and sending unit are clean and tight. A loose wire will cause the exact symptom you describe.
Jeff
 
Thanks Kimberly, Tony & Jeff. I'll check the connections and Tony I may just take you up on your offer if that doesn't fix it. The gauge does register correct when sitting still or on a smooth stretch of the road. Hit a bump and it goes from one extreme to the other. By the way why are there no baffles in a tank I had to pay a fortune for? As well as I remember the tank for the 64 was about double the cost of the one for the 80 /ubbthreads/images/graemlins/frown.gif


Naomi -- Owner of a 1964 MGB & a 1980 MGB. Both repaired over 4000 times and still loved
 
BMC started implementing the instrument voltage stabilizer (on the back of the gauges/dash) on most of its cars by late 1964. It sounds to me like you have a car built w/o the voltage stabilizer. Cars wired like that have "magnetic" gauges that respond instantly to changes. Later cars with the stabilizer used bimetallic, resistance heating type gauges.

If you want to run a "steady" gauge, and your new tank has no baffles, you'll need to add the voltage stabilizer and replace both the sending unit and the fuel gauge itself. Your husband is right that the early and later systems are not compatible but there's more to it than just the resistance range of the system.
 
Doug, my 'B' wiring diagrams don't show the voltage stabilizer until chassis number GHN3/U 48766, or 1965.
Of course, we all know how consistent they were with changes! /ubbthreads/images/graemlins/rolleyes.gif
Jeff
 
The '64 (384XX) here has a voltage stabiliser, so there ya go. I dunno if this car had the harness/guages/sender swapped, but who knows... I ~have~ found evidence of some hard "knobbling" on it. It's a "pull-handle," with an 18GB engine.

May have to start callin' it: "AllSorts." /ubbthreads/images/graemlins/wink.gif
 
I tried not to use a firm date on when the stabilizer showed up. It seems to have been implemented in several BMC cars (not just MGs) over months of production.
 
Understand. Just threw it up as corroberation of your and Jeff's observations.
 
I actually prefer mine bouncy. At least I know its working and when it gets to the "E" I'm still OK so long as its a "bouncy E". /ubbthreads/images/graemlins/grin.gif
 
A friend's wife threaten'd to get him a "Vanity" tag: "SNIF N E" as he'd invariably leave her th' car with the sender float bangin' th' bottom.
 
Hi Tony, Can't a voltage stabiliser be used with that guage to steady it.??---Keoke
 
[ QUOTE ]
I actually prefer mine bouncy. At least I know its working and when it gets to the "E" I'm still OK so long as its a "bouncy E". /ubbthreads/images/graemlins/grin.gif

[/ QUOTE ]

/ubbthreads/images/graemlins/iagree.gif---Keoke--- /ubbthreads/images/graemlins/laugh.gif
 
[ QUOTE ]

Hi Tony, Can't a voltage stabiliser be used with that guage to steady it.??---Keoke

[/ QUOTE ]
?????????????????????????
D
 
Adding the stabilizer will not improve the "stability" of the early gauges/senders. The non-stabilized systems used a gauge type that works kind of like a wheatstone-bridge. There are a series of electromagnets pulling on the gauge needle. The sending unit controls the current flow (and thus field strength) of "one side" of these balanced magnets. Since the magnetic field can change almost instantly the needle responds rapidly. You can see this by switching on the ignition and disconnecting the green/black wire from the sender. On cars without the stabilizer, pulling the green/black wire will instantly make the gauge read "full", grounding it will make it read empty. The systems with the stabilizer work in the opposite direction and respond slower because the gauge works by heating of a bimetallic spring element using resistance coils.

You can see the inside of these early gauges on the MGA-guru site:
https://www.mgaguru.com/mgtech/electric/electr_1.htm

A general overview of the later, stabilized-type gauges can be seen at:
https://www.nls.net/mp/volks/htm/fuel_ga.htm
(Yes I know it's a VW site... but the technology is exactly the same).
 
WOW, Doug! Thanks - I learned something new today

...& my grandmother said the day you don't look forward to learning smoething new is the day you should go ahead & die!
 
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