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MG MGA - fuel guage/sending unit problem

Gentlemen
As I am getting geared up for GT33 I decided it was time to replace the MGB fuel tank/sending unit and guage for an new MGA tank and sending unit and use an existing A guage that came with the car.
Here is my problem.
I beleieve I have about 1/2 a tank of gas and the guage is reading just above 1/2.
Ohm reading at sending unit shows 40 ohms which should be about 1/2.
When I drive the car the fuel guage will bounce wildly from 1/2 to full and will stick on full for a few seconds to a few minutes then start bouncing wildly again.
I added 3.5 gallons of gas and the guage reads 7/8ths full and the ohm meter reads 70ohms. The needle still bounces a bit.
I'm not sure where to start looking to figure out where the problem is.

Any suggestions????
Thanks
Kris
Kris Sorensen

Kris, Is the new sending unit an original or a repro? If it's a repro, that's where I'd start looking. I had one that used to behave in a similar manner. Finally got fed up with it and sourced a working original unit. It works MUCH better. Problem with the repro units is the resistor wire windings in the sender unit are poorly made and use a single wiper arm. See the attached photo of the repro unit that was in my car.

Andy Bounsall

Compare that to how the original unit in this photo was made.

Andy Bounsall

Andy
Yes it is a repro from Scarb. Faire. The windings on mine are red like your old one but I believe just a single wiper arm.

Kris
Kris Sorensen

Had the same problem; Purchased a repro that leaked & was very inaccurate; Found a used original & it has worked well for 12 years; There is a parts dealer in Kentucky who advertises in hemmings & usually stocks original sending units; Barry
Barrett Burka

Kris, suggest you have a look at Barneys MGAGURU site.
Lots of info there about gauges and sender units.
Totally agree with other responses though about repro sender units -- rubbish. Always try to get an original if you can.You must make sure of a good earth connection to the sender unit, even if necessary adding an earth lead from one of the mounting screws back on to the chassis. They also tend to have a problem sometimes with poor earthing from the float arm to the body of the sender unit. If this is so,try soldering a flexible copper lead on to the float arm and connect the other end to the body of the sender unit with a small self tapping screw.There is an article in the NAMGAR Tech Sessions about this. Volume 17/Number 4.
David
D C GRAHAME

Hi Kris,
You probably will find that the gauge reading will rise up and down as the actual fuel level drops from full since I believe there are no baffles in an MGA tank, and the fuel sloshes around as you fly through those curves!
My original one used to do what sounds like a similar thing, sometimes pegging itself to the F and returning. I ordered a new one and when I received it it had a sticker on it saying that it had passed a secondary "quality inspection" by a source in California. This didn't give me much confidence, so I tried cleaning the original one and running a ground wire as above and it works pretty well now.

See you at GT 33.

Ralph
Ralph

Gentlemen
Thanks for your help and suggestions.
Out of frustration I drained my tank and removed the sending unit today. I tested the sending unit to find the readings were real wonky. I called my local(50 min drive) Moss dealer to find he had one in stock. Threw the jack in the car and headed over there. Took 10 min. to change it and it seems to work fine.
Ralph
The new Moss tanks have baffles.

Now I have to try to return this one to Scarb. Faire

See you in Penn.

Kris Sorensen

Andy

What is the best material to use when sealing the cover on the sender. Mine is leaking. Gordon
Gordon Harrison

Hylomar original blue works great! Moss recommends it and sells it.
Jeff Bennett

Gordon
I agree with Jeff it worked great on mine. My unit leaked at the 4 screws that hold down the cover for the windings. I did have to change the gasket because the Hylomar didn't work on the thin cork gasket that came with it
My resolve to my problem was I purchased a unit from Moss and it works but I havn't fill it up to see if there are any leaks. The gaskests on the Moss unit are rubber so I hope that will be better.
I contacted Scarb. Faire and have arranged to take my unit to the GT for exchange for a muffler.
Kris
Kris Sorensen

This thread was discussed between 04/07/2008 and 08/07/2008

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