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Fuel Gauge and sender issue
https://ausmini.com/forums/viewtopic.php?f=2&t=100229		 Page 1 of 2
Author:  clip [ Mon Jul 27, 2020 6:21 pm ]
Post subject:  Fuel Gauge and sender issue
I've read heaps of posts and info but can't find an answer to this, so hopping someone here can help.
I have a new speedo head that came with new gauge and voltage stabilizer. The gauge never goes above 3/4 full mark (actually just below it). Checked the gauge by earthing the sender, and gauge goes to full. So went and bought a new sender! Hooked it up before pulling out the old one and bugger me, it still only reads to 3/4 when float is in the full position. So checked the ohms, it was wildly off - 270 empty and 33 ohms when in full position. Adjust it to read 222 on empty and 20 on full. Gauge still reads well under full. Adjusted it again but had to drop it to about 7ohms before I could get a full reading on the gauge. Why is this so? Is this going to be a problem? Could it harm the gauge? Thanks for any advice.
Author:  gtogreen1969 [ Mon Jul 27, 2020 6:30 pm ]
Post subject:  Re: Fuel Gauge and sender issue
Is there a part number on the gauge? It may be a 12v guage to suit an early car.
Author:  clip [ Mon Jul 27, 2020 9:04 pm ]
Post subject:  Re: Fuel Gauge and sender issue
Yep, I did check that, but all matching.
Author:  jimb [ Fri Nov 08, 2024 6:38 pm ]
Post subject:  Re: Fuel Gauge and sender issue
Hi Clip, I have experienced the same problem with gauge reading half full when tank is full. Bought new sender still reading the same. How did you adjust the readings on the sender.
Regards, Jim.
Author:  timmy201 [ Fri Nov 08, 2024 7:09 pm ]
Post subject:  Re: Fuel Gauge and sender issue
What’s the part number on the sender? Part number on the gauge? Have you got a voltage stabiliser?
Author:  Dave Dobeson [ Sat Nov 09, 2024 2:12 pm ]
Post subject:  Re: Fuel Gauge and sender issue
Clip.
I have had the same problem since we bought the car, 10 years ago. Where it reads when the tank is empty is more important than where it is at full. (And I am not game to fiddle with the gauge calibration in behind the speedo). My sender went from 30 ohms full to 240 ohms empty.
If the new speedo has an electronic voltage (10 volts) stabiliser then you can "tap off' the voltage at the fuel sender connection on the tank and run it to a separate high resistance electronic gauge. (I did this).
Unfortunately this won't easily work with an old fashioned original bimetal voltage stabiliser (fluctuating, on/off, 0 to 12 to 0 volts, that averages about 10 volts) as the voltage at the tank connection is not stable.
You can measure the voltage at the sender/tank connection relative to the chassis/earth/0 volts, with the engine running.
Stable? Good. Mine read 3.5 volts when full to 8 volts when empty. Unstable/fluctuating? VERY DIFFICULT.
I hope that this helps a little.
Dave D
Author:  drmini in aust [ Sat Nov 09, 2024 3:50 pm ]
Post subject:  Re: Fuel Gauge and sender issue
Mine used to read lower the faster I went. Then come back up as you slowed down,
The voltage stabiliser on the new 200 kmh speedo was rubbish and responding to road vibration.
A new electronic one from member 'wombat' fixed it.
Author:  Steam [ Sat Nov 09, 2024 4:46 pm ]
Post subject:  Re: Fuel Gauge and sender issue
You should also check where the actual float is when empty and full respectively.
I chased a false low to empty fault for a while before I found out that the float was hitting the tank side thus not dropping fully on low/empty. The float had been put on wrong.
Also if the float 8s full of fuel it will not read correctly, obviously.
Author:  Oscar [ Sun Nov 10, 2024 10:31 am ]
Post subject:  Re: Fuel Gauge and sender issue
As the doc alluded to I'd definitely be going for an electronic stabiliser. Easy job to do the mod yourself if you're handy with a soldering iron.
This link has instructions http://www.britishv8.org/Articles/MGB-Voltage-Stabilizer.htm.

Once everything's confirmed to be working then calibrate the fuel gauge by tweaking the two limit adjusters at the back of the gauge. You need to go back-and-forth a bit before it's correct. After putting up for decades with a gauge reading from just under full to 1/4 for empty (and yes I did stretch it out too far once and ran out of fuel :oops: ) I finally decided to recalibrate the gauge a few years ago. It now spans from Empty (with still a bit of fuel in reserve) to Full. Happy days!!!

Calibration instructions here https://www.theminiforum.co.uk/forums/topic/347966-checking-testing-and-adjusting-smiths-fuel-gauges/. Ignore the resistors. Just calibrate to your sender.

Hope this helps.
Author:  Steam [ Sun Nov 10, 2024 10:41 am ]
Post subject:  Re: Fuel Gauge and sender issue
Electronic stabilisers are definately the way to go, but I shake my head when I see all these over worked solutions.
All you need is a 10v regulator, no resistore, capacitors or diodes ( or leds you cannot see anyway) needed. Making a circuit complicated for the sake of it is plain bonkers.
Author:  Oscar [ Sun Nov 10, 2024 10:46 am ]
Post subject:  Re: Fuel Gauge and sender issue
Yeah I agree. I laughed when I saw that LED option... :lol:
Author:  Dave Dobeson [ Sun Nov 10, 2024 3:31 pm ]
Post subject:  Re: Fuel Gauge and sender issue
I used the ....britishv8.. instructions as suggested by Oscar and it has worked perfectly for 9 years. Granted the LED and its resistor and maybe the output capacitor can be omitted but the input capacitor is in ALL of the data sheets for LM78xx voltage regulator chips. There is a huge amount of electrical "noise" in a Mini and the capacitor helps to reduce this before it gets to the regulator chip.
Granted a second gauge might be an overworked solution, but I have never run out of fuel. And, if you think about it, isn't a Mini an overworked solution for a Morris Minor problem?
Dave
Author:  Steam [ Sun Nov 10, 2024 5:34 pm ]
Post subject:  Re: Fuel Gauge and sender issue
The noise will only affect the quality of the output wave, if this was for a stable supply then it would be needed but given the output the gauges are used to is about as unstable as it can get from the bimetallic strip then the input capacitor is not needed.
But please feel free to keep using them, they are so cheap anyway.
Author:  68+86auto [ Mon Nov 11, 2024 12:48 pm ]
Post subject:  Re: Fuel Gauge and sender issue
The LM7810 is no longer so easy to get. Neither Jaycar or Altronics sell it. The capacitors aren't needed.

There's not even a good option on eBay. Last time someone was looking for one, I found Wiltronics had an alternative in stock. https://www.wiltronics.com.au/product/6648/10v-voltage-regulator-ldo/

There are proper component suppliers which should have them but by the time you add shipping it becomes expensive. Even then, the big component suppliers don't come up on google as having them which is unusual.

I've thought of making some which can fit exactly like original without reusing the original cases. The ones which are currently available are expensive. There's one seller of an alternative which doesn't even supply terminals with it.
Author:  Steam [ Mon Nov 11, 2024 3:10 pm ]
Post subject:  Re: Fuel Gauge and sender issue
I have a number of Clubman versions here, if anyone needs one they can pm me.
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