Old car has a low oil level sensor, which has never really worked properly. And spares for it NLA.
It has a probe in the sump about 2" long, which merely screws in. Doesn't tell you the oil level as such - just warns if it gets too low.
I've looked for a modern aftermarket set (probe plus electronics) but can't find anything.
I've also no idea on the principle of how it works.
Anyone know of anything that could be adapted? Electronics obviously need to be able to work from a car supply.
If it never worked maybe it's not surprising spares aren't available. Apart from screwing in are there any other connections to it and what diameter might it be? There used to be a trade magazine called what's new in process control. If it's still on the go the adverts in there might be worth digging through?
Is the sensor a cylinder the oil can enter? If so I'd suspect it measures the changes in capacitance between the case and a central electrode as the level of oil changes.
Don't ask me about the electronics to convert that to a measurable signal: I opted out of electronics in favour of what seemed more useful at the time (eg nuclear).
Similar sensors from other cars of the period - eg Buicks?
If it's an old car, I'd guess it was something mechanical, like a switch with a diaphragm, or a float, or something. I'm surprised you didn't ask in uk.rec.cars.maintenance - I'm sure I've seen you in there before, and it's not completely dead.
Sadly not something as simple as a float. As I said, I dunno just how it works.
Reason I'm asking here is perhaps a fluid sensor from something like an oil tank for central heating? Or whatever?
No - it is a sealed unit. Hence not being able to guess just how it works. Or not.
As I said anything suitable has been NLA for some time. When I bought the car at about 3 years old, BL couldn't supply a spare sensor.
Dave Plowman (News) brought next idea :
The only one I have ever come across, used a pipe dipping down to the oil level. At the dash, you tugged on a button which had a concentric red/green indicator. The outer section stayed in as you pulled, showing green if the oil level was OK and the end of the tube below the oil level. If above the outer section would pull out showing red. You had to use it while the engine was off. It worked on the principle of the oil being harder to suck up the pipe, than air would be if the pipe ended in air.
The early ones in FIATs (Lancias, Alfas) were quite ingenious - and unreliable.
They only worked at ignition ON (once the engine was started they were ignored).
They were immersed in the oil, and there were a pair of contacts in the ON position, with a bimetallic strip and a heating element. (Much like a flasher bulb).
When the ignition was turned on, a small current was passed through the heater. If there was enough oil to cover the element, the heat would not be enough to make the BM strip break the contact and the light would go OFF. No oil = heater bends strip and light remains on.
There is some sort of bracketing circuitry in the head unit, as you can't get rid of the light by leaving the wires open or closed circuit. I'm guessing it also looks for a current draw for the heater. Because all the f***ed units I saw (and they were c. £50 a pop) seemed to have the heater wire broken.
If I had been designing it, I would have looked to some opto-electrical method. I guess there were ruggedness issues ?
Well, I didn't really think a float would do the job in those conditions (having had them puncture themselves in old carbs), but it was just an example of something mechanical that some optimist designer might have dreamed up in the past. I'd guess something that relied on negative pressure produced by suction to keep the contacts in a certain position. The missus once had a Capri, and I'm sure it had such a thing.
The phrase "electronic dipstick" turns up a few possible interesting devices, e.g.
Interesting, but rather too sophisticated for my use. ;-)
I did have an old Bentley with a float inside the sump. Just like in the fuel tank. Press a button next to the fuel gauge and it read oil level. Worked pretty well too.
My everyday car has an oil level system too - and no dipstick. But again, more than I need for the old car. Just want the original idea of a low level warning. Not just for me, but to do an article for the club mag. If I can find a reasonably easy to fit substitute.
The sensor on the outside is simply a sealed brass tube which fits horizontally in the sump via a threaded boss - I assume at the minimum oil level. With two wires going into it. BL manual no help as to how it actually works. The electronics (located behind the instruments) is badged Plektron.
Our first car (an ancient Avenger) didn't have a working fuel gauge - you had to shove a pipe into the filler and see by the wetness where the petrol had come up to. When I finally got round to fixing it, it transpired that whoever had put the seats in had crushed the wire between the seat frame and the floor. It was so obvious, we wondered if they'd done it just for the hell of it.
Same with my present and previous cars, I gather the dipstick tube is now relegated to a handy way of sucking the old oil out at service time, even the oil filter is positioned at the top of the engine to avoid any pesky bending down to reach it.
I can remotely monitor various readings from the car on my phone, it seemed like the oil was drained within a minute of them starting to service it ...
It is connected to the inlet manifold with apipe When the hole is immersed in oil, a vacuum is created. When it it exposed, there is normal air pressure.
So all there is, is a switch measuring the vacuum or lack thereof.
Sure it's not Pektron?
They did a shitload of electronics / relays etc for serveral UK car manufacturers I'm aware of their products on the Lotus Elise / Elan / Esprit and the K series engined MG/Rover)
Still around in Derby
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Another curious problem. What have we got?
A 2" sealed probe. Material? Is the probe electrically connected to the mounting boss?
Screws horizontally into the sump. Above/below/at the minimum level?
2 wires. Is one connected to the probe body and/or mounting boss? Are the wires open/short circuit or have some resistance? Does the state change/alter between plenty of oil and not enough oil?Digging about for the "low oil" cut offs for small engines, as I thought my diesel genset had one and that was just a bare probe so might lead some where. I found that they are mostly float switches or pressure operated but there is also an "electro-vibration" type:
Peizo element mounted in tube, with oil around less vibration, no oil more vibration, control box to generate appropiate signal. As it's piezo element one assumes if you took the probe out connected it to a 'scope and gently tapped or vibrated the probe you'd see something on the 'scope.
Brass tube. If you want, a bit like a large CTS.
It is screwed into the sump, so will have at least some degree of connection to that.
Impossible to tell. A guess would be at about the minimum level, by looking at the position on the sump.
There are two wires from it.
Never had a working one to do any tests on. Been NLA for ages, and used ones expensive.
Sounds exactly like the arrangement I described upthread. A current is pushed down the wires to the heating element and as long as the circuit stays closed you have oil.
Could still be a capacitive sensor but with the sump as the other "plate". Is one of the sensor's wires short-circuit to the sump?
I did say "from /other/ cars of the period" - which was in response to your "anything that could be /adapted/" [emphases added].
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