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Fuel Gauge reads only half full (or half empty)


Rich
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Hello all, 

 

After a fill up today i noticed that the fuel gauge only reads half even though the tank is full.  Ive never filled the tank to full before so its the first time I've noticed this.

 

All the other gauges and clocks work fine.

 

The car is a MK1 vitesse cabriolet, any help of advice as ever is greatly received

 

Many thanks

 

Rich

 

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If you have non stabilised gauges, ie the needles fly up to a reading not slow and damped you may find someone has fitted a stabilised float , this mix and match gives some back to front fuel reading

you need to half empy the tank remove the float and check it works out the tank.

is this a six hole sender or bayonet fixed ??

 

pete

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Just drive it and burn off some fuel to start with (so there's no risk of the level being higher than the sender hole), then pop out the fuel level sender.  Chances are you'll find the sender float half full of petrol due to a pin hole leak or maybe a miss-bent arm.

 

If it's a leaking float, replace it.  If not get the level down to the point you can empty the petrol in to jerry cans (if you disconnect the fuel pump feed you'll probably find it syphones naturally).  Pour a couple of litres back in and then set the arm so it's just lifted off the bottom test (a multi-meter set to resistance should help you judge this from outside the tank).  Finally put the fuel back in and fill 'er up.  You may not get a full needle when full - but you will know that an empty needle still means a couple of litres to get you to the nearest pertrol station!

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Hi,

 

Just in case none if the above works and you want the gauge to read correctly:

 

Mine also only reads 3/4 when the tank is full to the brim!  

 

I have checked and changed everything as described above apart from changing the gauge itself.

I intend to get my gauge re-calibrated over the winter period and will be sending the new sender along with it so they can be matched.

 

Will let you know how it goes !

 

Aidan

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so thats looking stabilised,  grey matter was unsure when this was introduced 

 

this could be heading for a stabiliser fault , make sure its earthed to the speedo and is right way up  they are marked  'top'

 

six hole stabilised sender seems rare ,  H and V are same sender , its the stroke not the tank width that makes it  the same .

 

if you short the sender to earth does she read full ??? if not suspect the stabiliser voltage is low , what the temp gauge doing ??? as they are all fed from the satbilised unit,   they give out about 10.5volts as a pulse   0-10-0-10  

 

Pete

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ive got a proper smiths test box that does the calibration settings, full and empty for all types of gauge and sender, not used it for years 

so need to read the book to get the wires on right. 

 

but its a long way to sunny luton 

 

I as with ign off they all read empty /cold then a higher voltage reads full or hot,  if its over reading the stabiliser could be poking out more than the pulsed  10.5 volts they should run at  

 

with the tank sender earthed it should just read Full   or a little over as the resistance is 18 ohm    full  256   empty   earthed is near 0 ohm.

thats with the sender having its location notch at the top ( the sender i have is not marked top) so this maybe inverted guess work.

 

my brains forgot about the ohms law and all that   but v=IxR  

 

so you could have a duff satbiliser or you need the gauge needle given a light 'bend' 

 

try to check the green wire feeds from stab to gauges for what volts are being produced 

 

the stab must be earthed and 'top 'at the top

 

solid state  ( e bay) ones dont have this requirement

 

Pete

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Ok, so i swapped over the positive with the negative on the sender and the gauge read 3/4! This is whats in the tank. so could this be the cause? Or is this what you mentioned Pete by earthing the sender?

 

I then checked the stabiliser at the back of the speedo and i got 12 volts from the wires going in and a pulsed  0 - 5-6 volts (sometimes a 9-10 volts) on the output wire which runs to the gauges. 

 

Im going to get a solid state stabiliser but has anyone fitted one of these and are they worth it?

 

Thanks

 

Rich

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there 's a lot like them , some have been unreliable 

no hard and fast info on how good they are 

 I fear its  hobsons choice 

 

the fact youre getting mixed voltages may indicate a problem ,  inside is a simple wire wound coil around a bi metal strip, this has a pair of simple contacts 

which open close    all i know is 0-10-0-10 is the normal.

 

            Pete

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Many thanks Pete, 

 

Ill have a look once i get it through the post.  In regards to the swapping of wires around on the sender, i put the neg on the pos and visa versa and it read 3/4. Could this be a fix or as you originally stated its just earthed to neg?

 

Many thanks for all your help by the way, you should open a garage  :)

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the two tags on the sender are one is to eath it to the body , lucar is welded to the float base,  the insulated one is the line to  gauge.

 

they earth the sender as its mounts and tank mounts are not good earthing points . ( dont want sparks outside the tank)

 

so it will probably  will work with the earth lead Off.   

 

if you link the sender green wire to earth it should give a more than full reading on the gauge  dont leave this on for long or you start to cook the gauge

 

 

 Rich, My mum always wanted me to have a garage she makes the cakes and scones and i scratch me head and get oily in the workshop  it never happened

 

42 yrs in truck manufacture , managed all the Vehicle and Unit Audits, smoke emission, warranty returns,  testing and tachograph calibration, 

so we being the factory ferrets  had a good understanding of  just about everything from  electrophoretic paint tanks to screen wash jets  

 

great fun till it was closed down in 93 , I departed in 2003,,,   just another lost industry in UK 

 

  Pete

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Pete

 

In respect of Rich's query in regard reversal of the wiring, Is it possible that reversing the wiring at the back of the Gauge would have the same impact?

 

Its always possible that previous adjustments ended up with these wires being reversed

 

It's something I have not tried yet (Tried most everything else!) 

 

Aidan

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My traditional voltage stabilizer failed and I got a replacement which also failed after 3 months. Then I bought a solid state one which has been working fine for 2 years.

 

There are some cheap and nasty solid state ones which contain just a voltage stabiliser. This one has additional components, capacitors, which are necessary for long life!

 

http://www.ebay.co.uk/itm/SOLID-STATE-VOLTAGE-STABILIZER-TR4-Dolomite-GT6-TR5-/131629262735?hash=item1ea5b7278f:g:ajsAAOxyUrZSzEu7

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Hello all,

 

Many thanks for all your replies. i managed to get a stabiliser from James P and found that its a solid state one but in the same guise as the original bi-metal one. Anyway fitted it today and both guages are working :) .

 

I put the multimeter on the B terminal and got a good 12-13v and on the I terminal a good 12v. Kinda suspect that i should be getting 10v on the I terminal going to the guages!

 

Could this be due to it being a solid state device? The broken original only pushed out 6 - 8v?

 

Its fitted anyway so i suppose i should check the output with the engine running and all the earths back on which may drop the out put volts.

 

Regards

 

Rich

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Rich,

If you check the voltage without any working load you can get battery volts on the meter not the

reduced Voltage you expect

 

 

solid state does not pulse like the old smiths units which do switch

 

and at 6v is running low, hence your low readings

 

never played with a solid state so blankety blank

ifnthebgauges now read too high , well its not working !!!! ¥££€€_%%/×

 

pete

 

pete

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