hello for the last two weeks my fuel gauge has been playing up it was reading on three quarters full, When it had just been filled up and petrol could be seen at top of filler neck.Now today when i filled up today for the low price of 149.9 it was reading on three quarters then dropped to under half before i left the servo. i was thinking maybe the float might be taking on petrol and making it heavier and giving me the low reading or that the gauge was faulty,or am i right in thinking that the sender unit is like a potentiometre and variable resistance on where the float is in the tank and if i had dirty conection this would cause more resistance and give me a incorrect reading or has my sender unit sh@t itself. your opinions would be much appreciated on this matter.

Cheers TUCK3R

I'd suspect the voltage regulator in the speedo. When they go flakey you get all sorts of weird results. A typical symptom is the fuel level varying (slowly) with engine revs. If you have more fuel when idling at the lights than you do when drivoing along, suspect the regulator.

Tim

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1951 Morris Commercial J Type Van
1955 BSA C11G
1961 Morris Mini Traveller
1969 Triumph TR6R
1977 Leyland Moke Californian

it doesnt vary with revs it just droped and wont go any higher and it stays constant its not erratic. how would i check for that behind the speedo and how could i test?

if the voltage reg on the back of the speedo is gone usually you will find the engine temp indicator will read high when the engine has only been running for a minute or 2 and is really still "cold", i would hazzard a guess and say that your sender is on its way out or has not been adjusted to suit your fuel tank. Yes it uses variable resistance.

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http://www.youtube.com/watch?v=nDMkVq1jRGU

My money is on the sender unit. Yes, you are correct it is just a basic potentiometer and easily checked with a multimeter if you have one. I think the side plate can be removed by bending the tags so you can have a squizz at the winding or the sliding contact to see if they are buggered.

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1967 Cooper S - new front bearings to do.
1965 Cooper S shell - Slow progress. No time or money!
1966 Deluxe- next rustoration!
Mk 2 & XJ6 Jags. Less said the better.

Use an old cricket stump and measure it that way, more reliable than those blasted fuel gauges.
ive got a collection of petrol tins now from everytime i've run out of juice.
Maybe i should just change the float?

Not as silly as may sound. Many light aircraft pre/post flight checks includes a check of fuel levels in wing tanks the same way. But maybe not with cricket stumps.

Then again, aircraft fuel guages stuck on full is slightly more inconvenient.

_________________
1967 Cooper S - new front bearings to do.
1965 Cooper S shell - Slow progress. No time or money!
1966 Deluxe- next rustoration!
Mk 2 & XJ6 Jags. Less said the better.

its all fixed ended up being one of the connections had started to work its way loos so i removed cleaned up and soldered new terminal on the sender thanks for all your replays much appreciated.


cheers TUCK3R