Question for the panel

Its probably completely irrelevant in this case but ...

Things that float in water may not float in petrol - the difference in specific gravity is around 30% :-\

Well, it's not irrelevant. But: When I shook the float around, there was no sound, nor feel, of anything inside it, such as petrol. Saying that, the fact that the float did not appear to rise as it was lowered into the tank is the only clue I have at the moment. This is a definite puzzle, and I'm not sure where to go next with it.

well ... if the float was completely full of petrol it might make no sound at all when you shake it, and the thing would still float in water.

I assume its not one of those semi-transparent plastic float things ?

If it was still attached to the sender unit when you tested it, then it would have been difficult to deduce anything from the weight of the complete assembly.

If its feasible to do so, I might be inclined to detach the float from the rest of the works, and see if it floats in a small cup of petrol ?

Failing that, you might learn something by waving a hairdryer at the float.

When I tested the float, it was not attached to the rest of the transmitter, only to the wire that connects it to the transmitter.

It is a soldered brass item, and does not feel unduly heavy.

I suppose I could use a firelighter and see if the float combusts?

I might remove it, and try it in petrol, as suggested. I have a convenient can of petrol in the garage.

While you are at it, it might be an idea to completely submerge the float in a jug of warm water, and see if any bubbles (or anything else) appear. Don’t use boiling water as it might easily split the float.

If you eliminate the float as the cause of the problem, then the next thing I might try is to stick the whole assembly back in to the hole that it came from - but this time attach a piece of string to the float so that you can pull it to the surface. (You state in the OP that you cannot see the float while it’s in the tank ?)

That will make sure that the float is in the "full" position and the gauge should react accordingly. If it doesn’t then I suspect you have some weirdo electrical fault.

btw ... I am wondering what an INconvenient can of petrol might be - apart from the one in the shed when it catches fire :-\

Good ideas, both. I will see what I can find put. I will report any outcomes. Thanks.

I think your definition of an inconvenient can of petrol is spot-on. Apart from one that is not to hand.

The other possible explanation that you haven't examined is when fitted in the tank the unit has to be fixed in so that there is no fuel leakage. Is there anything in the fixings (gasket, captive nuts etc) that might be preventing the float from rising fully when it is in position that wouldn't be present when the unit is removed?

Also, the latest E10 (10% additive) Unleaded does separate out if left for a fair while in an unmoving position. I found my Morris Minor was a swine to start if I left it for more than a fortnight because the E10 additive settled out in the float chamber and I had to wind the engine over long enough to use up the additive which won't start the engine to get to the petrol without it, which did then start the engine. I ended up using Super Unleaded which is "up to E5", and Esso's Super Unleaded has zero of the offending additive. The reason why I mention it is that the additive is clearly more dense than the petrol it is mixed with, so if it settles out in the petrol tank then there will be a density gradient from bottom to top, and that might affect the level the float rises to. Can you give your fuel a good stir through the hole where the float unit fits? That should mix the additive back in.

Jim

Nothing that I can think of. I had a good look when the sender was last out, and there is nothing anywhere near the float.

Now that is a definite possibility. The car has done very, very few miles during the last year, so what you describe is a definite possibility. When I remove the sender the next time, I will take a large wooden spoon and wave it about in the tank.

Early in the year, when I was not doing much of anything with the car (too cold), I did notice that the gauge was reading Low, so the next time I filled my main car up, I also filled the spare can, and put some in the tank, and some in the tank of an old Honda that is SORN'ed and sits outside, I run both cars' engines periodically. I did not keep any estimate of the amount of fuel that I added to the tank, and when I started to drive it again, believing that it was nearly empty, according to the gauge, I was amazed to find it only took a few gallons. Which started this saga.

The inspection and tank mixing might take place tomorrow.

The results:

1. Before doing anything, I read what the gauge was saying: ~ 1/2.
2. Removed sender unit, still wired, and laid it on the tank top.
3. too wooden spoon, and found it was bigger than the sender hole.
4. Found slat of wood, cleaned it, and did as much swirling around of the contents of the tank as possible. Could not guarantee that there was good mixing vertically, however.
5. Installed the sender temporarily, switched power back on, gauge read, if anything less than it had before.
6. Measured, and logged for future reference, the resistance of the sender at both ends of travel.
7. Removed float and its attached arm, and took it to a plastic pot with some fresh (~3 weeks) petrol. Was surprised to find that it did not float as high as I expected. When I pulled up on the arm to level the float out, only a small part of the float was above water. This seems to corroborate the strange or affected petrol theory. On close examination, the float did indeed feel a little heavy, but I really don't know what it should feel like if genuinely empty. I have left the sender unit outdoors, to let it drain, if possible, and if there is any petrol in it. I will look at it again at the weekend, and test its flotation again.

I think that we are close to an answer. What to do if the petrol is 'bad'? Obviously, when buying new fuel for the car, it would be worth buying E5. A good idea anyway, and with the amount that I use, it's not going to break the bank. Before, then, I could empty my petrol canister, currently filled with good petrol, into my main daily car, and then pump the old fuel from the old car's tank into the canister, and move it that way, one canister at a time. Hmmm.

Regarding item 7 on your list ...

"Was surprised to find that it did not float as high as I expected"

If you don’t know how high it floats when its working properly, then there’s a lot of potential to get yourself confused.

As my late father used to say "if you don’t know how something works, then you are going to have a hard time working out why it doesn’t work" :-\

I won't argue with that, but it's the only thing that makes any sense in this scenario.

I did the warm water test today, and I think I used too-hot water. But it proved interesting, there was suddenly a gush of bubbles and a strong smell of petrol. I kept it submerged, and it just kept on going, (like Felix). I knew that I had probably opened up a hole or a seam, but so what, there certainly appeared to have been fuel in there. By the time I withdrew it from the water, there was a horrid brown scum, and the kitchen smelled of petrol. I am now running the hob extract fan, for several hours, I expect. And the float now feel as though it weighs less. Conclusion: There had been a small leak, letting fuel into the float. So now I need to find a replacement brass float. Hard to do, and it needs to have the soldered wire arm. I could go to a plastic float, but I would still need an arm, although I could probably cobble something up from a piece of spare wire. All floats that I can see online either come without an arm ('armless?), or come with a full sender unit attached. More hunting to be done. This might do, at least it is affordable (shame about the float being plastic, but needs must):

No chance of attacking it with a soldering iron then ? - thats how most of them are stuck together.

If you are not able to do it yourself then any retired plumber over the age of 90 would probably help you out, as long as you could find a pack of Woodbines to pay him with.

Alternatively, the object of your affections on eBay does look seductively cheap, however ....

I might be inclined to send the vendor a message to clarify the resistance - I think you said yours was around 100 ohms, but he is quoting 260 for his ? If thats true then its not going to register anything much unless the tank is more than half full

You never know, he may have or know of a source of 100 ohm senders :-\

I suggest you measure the arm on your existing one. 30cm is about a foot in old money. They seem to come in a range of sizes from 4 inches to 14 inches, and you ought to replace like with like. I would suggest doing that and buying a suitable temporary fix because if my "afterthought" below doesn't work or you don't fancy the effort, you will still need a reasonably accurate fuel gauge.

I did find a brass float -

As an afterthought - it is possible to solder brass.

1. If you put your existing one in the oven and heat it to about 115C for a while, it should gradually evaporate the fuel inside it, and you know that there is a leak because when you put it in hot water before, petrol escaped. So by baking it you should eventually evaporate all the petrol inside.
2. Then let it cool, and finally put it into the fridge for an hour to get it to a cold temperature.
3. Now get a bowl of hand-hot water, take the float etc out of the fridge and immerse it and watch for where the air bubbles escape from as the air inside heats and expands. Mark it with a marker pen so that you can find the leak location(s) easily.
4. Then put it back in the oven for a while to evaporate any water that crept inside during action 3, then let it cool to room temperature.
5. Now with a bit of flux (or flux cored solder) clean the leak location with a soldering iron and then fill the leak with solder.
6. If it all goes well once you have sealed the leak(s) with solder, test it again in hand-hot water and confirm no bubbles show now (or mark the next leak and solder that like you did the first) and you will (eventually) have restored your original unit.

Jim

In this case, I would only use the arm and float. I can't find a source of those alone, this is a viable way to get them.

That is certainly a possibility. I will think about it. Thanks for the thoughts.

Yes, the postage is four times the cost of the float! Pass on that one. The afterthought is much more sensible, and do-able.

I have recently soldered over a hole in a carburettor float, and if my experience is anything to go by, you would be wasting your time with any electric soldering iron.

I have one of those hand held solid copper things which weighs over a pound, along with a propane torch.

I had wondered abut that. My soldering iron is a 25W electric, and while it is fine for repairing electrical components, I doubt that it would work on a larger mass of metal such as a float. For the cost of a suitable iron, I might as well buy that sender with a float attached, and save my self the hassle of soldering. Thanks for the corroboration that it be difficult to do with what I have.