Ran out of fuel!

[Tashman]

Recently bought a W123 300D and today it ran out of diesel while the gauge still read a quarter!
I walked to the filling station, brought back a gallon of diesel, poured it in, primed the pump and it started up again - still reading a 1/4!
Then drove to the filling station and filled it up with 60 litres of diesel and the gauge read full.
Why is the gauge doing this and how do I fix it?

 

[dougjoy]

Is this the first time this has happened, if so are you carrying anything electrical in the boot, like an alternator or anything with coils in it. If so this can give you a false reading.

If not then a full earth on the fuel tank sensor gives you a full reading, if you disconnect it the reading should be empty.

The fuel level unit is just a variable resistor with a float and they can go faulty.

Check your mileage against the fuel guage reading and see if it was just a glitch and hope it falls below the quarter this time when you expext it to.

Good luck with finding it.

 

[Tashman]

Is this the first time this has happened, if so are you carrying anything electrical in the boot, like an alternator or anything with coils in it. If so this can give you a false reading.

If not then a full earth on the fuel tank sensor gives you a full reading, if you disconnect it the reading should be empty.

The fuel level unit is just a variable resistor with a float and they can go faulty.

Check your mileage against the fuel guage reading and see if it was just a glitch and hope it falls below the quarter this time when you expext it to.

Good luck with finding it.

Thanks for explaining how it works. I've only had the car a week. Nothing electrical in the boot.

So by disconnecting the fuel tank sensor the gauge should read zero and the sensor is faulty.
If instead the gauge just drops to 1/4, then the sensor is fine and the gauge is faulty?

When it ran out it was definately empty - i know because it took 5 litres from the can and 60 from the pump - the manual says the capacity is 65 litres.
The yellow light didn't come on at all.

 

[dougjoy]

Agree, it is usually the float sensor an easier job.

 

[wireman]

Your tank unit is probably well worn, if you dont want the hassle of replacing it:-

Fill it up, zero the oddometer/trip counter and run it untill you think its about to run out again (perhaps getting close to 3/8 on the gauge), check the miles youv'e done and fill it again. Compare the amount you use with the 65 litre capacity and from then on you can zero the trip at each fill up and use that as a guide to the tank contents.

 

[Tashman]

Now replaced the float sensor unit in the tank, but its just the same.
Sometimes when driving along the fuel gauge will just jump to a half from a quarter!
Any more ideas?

 

[roadhog]

I'd start looking at the wiring. If, as per a previous post, the system looks for an earth for a full reading then a chaffed wire may well give you your symptoms.

 

[Tashman]

This might be related - my shoes had oil on them after driving...
took the lower panel off, and somethings dripping very slowly on the back of the dashboard!!!
How do you take out the dashboard clocks to inspect them?

 

[television]

Did you check the reading on the gauge when the float was disconnected

 

[Doug1234]

This might be related - my shoes had oil on them after driving...
took the lower panel off, and somethings dripping very slowly on the back of the dashboard!!!
How do you take out the dashboard clocks to inspect them?

Sounds like brake fluid dripping down from the rear of the servo then running down onto pedal mechanism and then dripping onto your shoes.

 

[Number_Cruncher]

The oil will most likely be from the pipe to the oil pressure gauge. If so, replace the pipe NOW - if the pipe fails completely, it will spray the inside of your car with engine oil very quickly and very effectively!

 

[Tashman]

Its definately engine oil.
I've just removed the panel under the steering wheel for a peep and theres lots of black drips coming down from the instument cluster.
What holds in the cluster because I can't see any bolts or screws.
Is replacing that pipe easy?
Could this oil contamination be whats causing the fuel gauge to play up?

 

[television]

The cluster just pushes out, from the rear,,its doubtful that oil has gone into the cluster but you never know

http://www.detali.ru/cat/oem_mb2.as...+++717.400&CT=F&cat=222&SID=54&SGR=585&SGN=13

 

[stever]

Easiest way to get the cluster out is to remove the panel underneath, reach up and push it out. Take the opportunity to replace the cluster lights if they need doing.

 

[Tashman]

Right,
pushed the cluster out, disconected the electrical connector, speedo, and oil pressure line, cluster comes out. The oil pressure line is dry so I start dismantling the cluster - it comes into 3 sections (speedo, clock, and Oil/temp/fuel gauge) The oil/temp/fuel one has oil dribling out of the oil pressure part that looks like an old pocket watch inside. Anyway I conclude the OP line is fine but the gauge is knackered so wandered into mercedes benz brentford thinking it might be thirty quid maybe (I only paid £400 for the car) and they tell me it has to come from germany and costs
£344!
So what now?

 

[television]

There are plenty being broken and that fault is rare, so you will pick one up quite cheap

 

[mattkh]

....I only paid £400 for the car

Hi
To make that car today would cost ten thousand pounds.

 

[Tashman]

i had a look on ebay for cars breaking but they were all petrol models which have a different set of dash clocks

 

[mattkh]

.....so wandered into mercedes benz brentford

Hi
What nostalgia.
Do you have their address ?
Is there any breakers yard close to you, the one I know is miles away from you.

 

[Top Cat]

i had a look on ebay for cars breaking but they were all petrol models which have a different set of dash clocks

Is there someone on here currently breaking a model similar to yours, have a look in the 'spares' section of the site