Fuel Tank Sender Unit

[4129R]

Can anyone confirm that a Smiths TBS 1514-003 fuel tank sender unit for a Triumph Herald/Vitesse will fit a TC tank? It also has the reference 215846, and is available from Rimmer Bros.

Is it the right length? An MGB AHU 1027 is the right sender, but the arm is too short, and rather than attach a longer arm from the original, I thought the TBS 1514-003 looked the same as the original.

[Dilkris]

Can't help with the question but my original sender (TCS) is out and readily accessible if you need dimensions or a any photo's. 

[4129R]

Can't help with the question but my original sender (TCS) is out and readily accessible if you need dimensions or a any photo's.

Thanks, but I have 2 rusted ones as patterns.

I have ordered the Herald one on eBay. I will report if it is the same length and fitting.

They must have got it from some normal car. They did with nearly all the other parts.

[4129R]

I have just measured the travel of the fuel tank sender unit.

Its full travel in 12", whereas the tank is 21" tall.

So for 9" of fuel level change, the sender unit will not register any movement.

That means it is only actually measuring 57% of the fuel movement, and for 43% of the time, it is not moving at all.

No wonder it stays full for a while, then empties quickly, then still has quite a lot of fuel left as the sender is not recording any movement.

I suppose that is what happens when you use a tall tank and a sender that describes only a small arc.

[Dilkris]

Does this mean that when the fuel tank gauge reads "E" - you still have (for a TCS) 9"of fuel in each tank?   

[4129R]

Does this mean that when the fuel tank gauge reads "E" - you still have (for a TCS) 9"of fuel in each tank?

I have not measured where the float is at its lowest point. I will do that when I fit the new sender, after I either run the fuel level low, or drain the left tank.

[4129R]

I managed to take some measurements.

The sender is central to the tank, so 10.5" above the bottom.

The float bottoms out 7.5" below its centre, so when it is reading empty, there is still 3" of fuel in the tanks = 1/7th full.

If the full travel of the float is 12", the float will be 15" above the bottom, so it will still read full when you have used 6" of fuel = 2/7th.

Since the US/UK cannot agree about the size of a gallon, (or even the spelling of litre), the fuel tank capacity is supposed to be 57 litres.

So when it first reads empty, you will have 1/7th of 57 litres = say 8 litres left.

It will still read full even after you have used around 16 litres.

So I believe the gauge measures from 8 litres to 41 litres in its full travel so it measures only 33 litres from empty to full, so 1/4 full would be 8 + 8.25 = 16.25 litres, half full would be 8 + 8.25 + 8.25 = 24.5 litres, and 3/4 full would be 88 + 8.25 + 8.25 + 8.25 = 32.75 litres. 

E = 8 litres or less.
1/4 = 16.25 litres
1/2 = 24.5 litres
3/4 = 32.75 litres
F    =  41 litres or more.

(If the scaling of the gauge is accurate !!!)

[Dilkris]

I admire your tenacity and thoroughness - the data is good to know - I for one will file it away for future reference.

[4129R]

While I am waiting for the new fuel tank sender to arrive, I am making up a dipstick from a thin length of wood.

I am going to calibrate it every 50mm from bottom to top.

The height is 21" = 530mm.

500mm = 54 litres
450mm =   49 litres
400mm =   43 litres
350mm =   38 litres
300 mm =  32.5 litres
250mm =   27 litres
200mm =   21.5 litres
150mm =   16 litres
100mm =   11 litres
50mm =    5.5 litres.

All measurements are to the nearest half litre.

57 litres equates to 15 US gallons. So 21" equates to 15 US gallons, so it is roughly 1.5" per US gallon for the two tanks.

Don't forget to put the dipstick in the tank without the fuel tank sensor, or you might damage the arm and the float. I think all sensors are located in the left hand tank only.

Well................... I have just calibrated and used my dipstick, and it shows me fuel is not passing from the left tank to the right tank through the balance pipe. I shall have to clear out that pipe when I drain the tanks to fit the new tank sender when it arrives.

[jbcollier]

Fun with math, sure...

You have a number of baked in assumptions that make your calculations suspect.  For example:

You are assuming linear travel gives linear effect.  This unlikely as the variable resistor is wrapped wire.  Some are even deliberately wired asymmetrical.

The same again for tank volume.  Determining how many gallons will result in "x" inches of increase in surface height is best done by experiment with a calibrated measuring container.

Finally, gauges are calibrated to read empty and still have some fuel remaining for good reasons.  The most obvious being, to make sure you do not run out of fuel even when you are not paying proper attention.  Also water and contaminants tend to collect in the very bottom of the tank.  The intake is often set a bit higher than you might think to avoid sucking this muck up.  No point in measuring what isn't actually available.

[4129R]

Fun with math, sure...

You have a number of baked in assumptions that make your calculations suspect.  For example:

You are assuming linear travel gives linear effect.  This unlikely as the variable resistor is wrapped wire.  Some are even deliberately wired asymmetrical.

The gauge readings are not linear, I assumed that was to correct the arc v straight line conflict. There is a similar disparity on the temperature gauges, which I thought was to correct non-linear variations.

The same again for tank volume.  Determining how many gallons will result in "x" inches of increase in surface height is best done by experiment with a calibrated measuring container.

The tanks are uniform cross section, so I believe this is a reasonable assumption.

Finally, gauges are calibrated to read empty and still have some fuel remaining for good reasons.  The most obvious being, to make sure you do not run out of fuel even when you are not paying proper attention.  Also water and contaminants tend to collect in the very bottom of the tank.  The intake is often set a bit higher than you might think to avoid sucking this muck up.  No point in measuring what isn't actually available.

I have measured the pipe at the bottom, and it is only about 10-15mm from the base.

[dakazman]

  My S2 sender new from a vendor had a intermittent open, when I first received it here,
 https://www.lotuseuropa.org/LotusForum/index.php?topic=2058.705
   and later found this;
  https://www.lotuseuropa.org/LotusForum/index.php?topic=2058.705https://www.lotuseuropa.org/LotusForum/index.php?topic=2058.795
   It works now.
Dakazman

[4129R]

Well the Triumph Herald/Vitesse fuel gauge sender arrived today.

It is very similar, but with a very slightly shorter float arm.

As the fuel tanks are only 11" wide, the arm cannot be long or it will hit the side of the tank.

This arm is 10" long, so very close. Same fitting to the hole in the tank, same electrical connections.

[314159td]

Noticed this just a bit too late - I have that part on my Herald electrical shelf right now. iirc there are ~two standards the Smiths gauges and senders were made to (different resistance sweeps, the third one is close enough usually). Your gauge may not match for whatever reason. I've had good and bad luck with wherever Rimmer is getting those parts from - sometimes I get a sender that shouldn't exist and have to use resistors and such to get it closer. 

[4129R]

I have just measured the resistance on the Triumph Herald/Vitesse sender unit.

On empty, it registers 246 ohms. On full it registers around 25 ohms. Those figures correspond to the table posted here:- http://lotus-europa.com/manuals/misc/electrical/gauges.html

Sadly my gauge climbs no higher than 3/4 full when the sender is at its highest. It seems I have a reluctant/tired fuel gauge.