Land Rover Repair: Gas Gauge down - sender unit problem?, gas gauge, fuel gauge

Question
QUESTION: This morning, my wife called me after leaving for work,
thinking we had been stolen a full tank of gas, the gas
gauge  was down like empty and the alert light was on. But
after trying to pump gas into the tank, she realized it was
the light. May be a fuse? something else?
Nothing else is wrong otherwise.
Thanks

ANSWER: Hi Juan,

sounds like the fuel pump 'sender' unit is not working.  If I'm right, there is a float lever that (in essence) sends the fuel level to the vehicles 'computer'.  It could be the lever but most likely the electronic sender/rheostat that actually sends the info.  This is all found on the fuel pump and would have to be replaced.

If it was a fuse or relay, the fuel pump would not be working and you would never be able to start the engine.   

A remote possible cause could be the dashboard itself but its highly unlikely.

Best of luck,

JohnMc




---------- FOLLOW-UP ----------

QUESTION: John,
Is this something that needs to be taken care of right away?
I mean, if rheostat is failing, could be dangerous? Could
affect something else? or we just have to watch the gas on the
tank and drive normally until we want to spend 500 bucks?

Answer
Hi Juan,

if you can start the Disco without any difficulty, I would think it is most likely the sender unit (a problem that is not quite common with LR's).  

IF it is the sender unit, it could mean that the something in the fuel you may have coated the material to affect its ability to measure resistance - the fuel level.  IF this is the case, you'll get incorrect readings of the quantity of fuel in your tank.

I cannot think of any danger from this possible problem - except if you overfill your tank while pumping.  I've known a few owners who drive without a fuel gauge - eventually they'll come up with the mortgage money to get the dealership to do the repair.

Meanwhile, you could probably drive with a inoperative fuel gauge so long as you realize it is not working and plan accordingly.  For example, if you get 600kms per tank - fill up every 500kms or so.

If you are interested in my THEORY, here's what I think may be the problem:

There is a known problem with certain fuels and fuel tank senders.  For example, on certain models of GM cars and trucks, the level of contaminents/additives? in the higher octane fuels can disable the ability of the sender unit completely.  A friend of mine (who lives in the South) lost his fuel gauge twice because of the fuel he uses (same as LR's).  The second time around, he was able to use additives to slow the process down BUT it eventually happened anyway.  The only fix was to replace the sender unit.

There is something in the fuels (mostly in the South) that destroys the resistive ability in the sender units.  Owners in Northern US don't seem to have the problem as much.  If you need to know more you could do a web search on fuel gauge failures and Corvettes, for example.  Well, that's my 10 cents worth.

There is another not-so-common problem with LR fuel pumps.  The plastic float device attached to the arm that is bouyant (which moves along the material of the sender unit...) is normally air tight.  It has been known to develop a leak and if that happens, it will not be as bouyant anymore.  The fix would be to remove the fuel pump and either replace the float or the entire pump.  Dealers would not mess around with parts like that (in order to save time and generate income) so they'd most likely replace the pump.  

I hope this enlightens you and gives you a better idea of what's going on your vehicle.

Regards,
JohnMc