UK Monster Owners Club Forum .: Technical :. Mods & How To's » Repairing the low fuel warning light.

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Old 07-08-2021, 12:48 PM   #1
PPuxley
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Repairing the low fuel warning light.

I said Id post when I had repaired the broken fuel sender. There are actually plenty of Youtube videos covering this , but here it is specific to a 1995 M900.

I had pulled mine apart to see what went on inside and went further than required for this repair. So some of what you see in my photos is not what you will have if you follow this. I didnt photograph it as it came apart unfortuneately.

In researching this I was amazed at the arguments generated in comments to videos when people realised that you were putting a heated electrical circuit inside a petrol tank.
However this is common practice. Afterall submerged electrical pumps where the fuel flows right through the electrical parts are also common practice.
With this particular thermistor in this application it gets warm but I was able to hold it between thumb and forefinger without discomfort. It takes about 30 seconds to 1 minute to light the lamp when removed from liquid.

There is a video of it working Here
I know Im running it through the oil warning light, it was just the first one to work when I was tracing it through the plug

The photos are in an album HERE




This is the Thermistor I used

1. De-solder the wire coming through the tip cover

2. Very carefully grind off the swage that holds the top cover in place. Only grind off the minimum you need to get the cover off. The idea is to leave enough to be able to peen it over when it comes time to refit it.

3. Withdraw the cover

4. Snip off the old thermistor as near below the chip as possible to leave some of the cable to solder onto





5. Prepare the thermistor and solder onto the centre wire you have just cut. It is very important that none of the wiring below the Thermistor is able to ground on the earth of the casing. In my repair I insulated it with some PVC cable sheath (I wasn’t sure how heat shrink behaves immersed in petrol)

6. Replace the cover pushing the Thermistor wire through the centre hole, and solder in place. Make sure the other 3 radial holes are not blocked

7. Because the connection of the tip cover to the base of the sender may be compromised electrically I extended the return cable (black) to connect directly to the Thermistor return wire.



8.Carefully re-swage the cover to the base with what you left of the base swage when you ground it away. I did it resting on a slightly open vice and tapped the base over the flange of the cover. Im sure those with a lathe could find a more elegant solution.

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Old 07-08-2021, 02:12 PM   #2
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Quote:
Originally Posted by PPuxley
...putting a heated electrical circuit inside a petrol tank...
or indeed, sticking 15L of petrol just above a hot engine (and between your knees!)

It'd have to reach somewhere in excess of 250c, perhaps as much as 400c, before you reached the flash point of unleaded fuel.
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Old 07-08-2021, 03:38 PM   #3
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or indeed, sticking 15L of petrol just above a hot engine (and between your knees!).
I knew those Gold Wing things were popular with “Sensible Types” for a reason!
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Old 07-08-2021, 03:39 PM   #4
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How many gallons of fuel are there over your knees in a classic beetle?

Edit: About 8.8, but it doesn’t all run onto your knees unless the rust holes are very low down!
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Old 07-08-2021, 03:40 PM   #5
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or under your butt in a landover
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Old 07-08-2021, 03:48 PM   #6
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Quote:
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or indeed, sticking 15L of petrol just above a hot engine (and between your knees!)

It'd have to reach somewhere in excess of 250c, perhaps as much as 400c, before you reached the flash point of unleaded fuel.
It really was quite surprising the reaction. And often from people who you could tell were otherwise technically minded.


Just been out to the garage having left it on test for a couple of hours in air. The light remains on, drawing about 140mA.
If force heated it tops out at around 180mA when the lamp reaches full brightness. So its not going to light the lamp to full brightness in use and maybe in particularly cold weather it may be too faint.
Therefore my Thermistor selection may not be quite correct.
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Old 07-08-2021, 03:58 PM   #7
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or indeed, sticking 15L of petrol just above a hot engine (and between your knees!).
I knew those Gold Wing things were popular with “Sensible Types” for a reason!
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Old 07-08-2021, 08:20 PM   #8
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Spare a thought for the young lads who climbed into Spitfire and other type cockpits behind 100 gallons and more of Avgas!
Any spills run to the cockpit floor as the so called firewall doesn't reach the bottom and that's before any bullets get involved.

Great work with the repair. I've pulled them apart before and had no idea what the amorphous brown blob on the end was!
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Old 09-08-2021, 03:34 PM   #9
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Proof of concept for an opto sensor for the the fuel level
VIDEO HERE


Proposed Method. SUPERCEDED BY LATER EVENTS , SEE POST 11
Possible pitfalls: Durability of sensor in fuel and whether there is good earth continuity between probe and tank.
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Old 09-08-2021, 04:06 PM   #10
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Module working. You can hear the 12V relay working, but just driving an led for now, but relay will handle much more than the current draw of the dash lamp.
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Old 10-08-2021, 02:40 PM   #11
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Finished my trial of a revised Fuel sender for the Ducati Monster.

At the moment the new probe is unshrouded, so is potentially subject to sloshing and surge, however I have put a 2 second stabilizing delay in the code to mitigate this.
Nevertheless I will probably put a shroud around it to completely eliminate those possible effects.
It works on the bench. But only time in proper use will tell whether its a worthwhile enterprise.
I have had a 2nd sensor immersed in petrol for 48hrs now and it is showing no signs of melting, swelling or the polycarbonate lens clouding, so- so far so good.

All details here.
https://flic.kr/s/aHsmWnCEd6

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Old 10-08-2021, 06:28 PM   #12
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Your dedication to sorting this out is admirable.
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Old 10-08-2021, 08:51 PM   #13
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Your dedication to sorting this out is admirable.
Ha! Waiting for various bits to arrive so I can start building the motor back up.
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Old 22-08-2021, 12:53 PM   #14
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Is there any update on the Optical Sensor Trial ?

How does it compare and what is the advantage to the Thermistor repair.

I'm guessing it's much more expensive than a 4 Thermistor.

Only asking as I'm looking forward to when mine fails at 120 to replace.
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Old 22-08-2021, 04:43 PM   #15
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Is there any update on the Optical Sensor Trial ?

How does it compare and what is the advantage to the Thermistor repair.

I'm guessing it's much more expensive than a 4 Thermistor.

Only asking as I'm looking forward to when mine fails at 120 to replace.
Not really. I did play around with a different module that just used a delay relay, which gets over having to programme a board. In terms of cost it wont be expensive in parts, probably less than 20. But its really only viable if you can build it oneself, which will take a couple of hours, I would guess.
I will get back on it when I run out of the main build arts again!
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