thanks for the link. I checked it out and was not able to find out too much. There appear to be several different sensor types, and the only thing I can come up with is that there is some sort of density/proximity/magnetic sensor inside the barrel guides in the LS 400 oil level sensor. I tested the float for magnetism, but did not get any reaction. I am attaching some pictures I took in the hopes that someone here will know exactly how these darn things work.
It looks like all the magic is inside the float guide and the float pivot, since the float itself is completely insulated from the electrical connections; the connector and wiring are simple enough, and the wiring appears to be a closed circuit as shown by the top of the float area. Somehow, the rising and falling of the float changes the voltage across the two leads from the barrels!??? I am sorely tempted to unsolder (?) one of these to see what exactly is inside, but would rather wait and see if anyone here has any insight!
Would either of you very knowledgeable gents know how the LS400 Oil Level Sender works? I took one apart and it has two leads that are connected to what looks like a simple float type mechanism. However, this float does not have any connections at all! The float itself is free-floating on an insulated plastic pivot and seems to be some sort of very soft carbon material that covers a brass peg. The float appears to be able to slide up and down its pivot and another thicker brass peg as the oil level rises and falls. However, the peculiar thing is that both ends of the float have semicircular grooves sort of like an open-end wrench/spanner, and both the pivots seem to have something soldered within them, as evidenced by wire ends in the solder!? I don't think these are as simple at all, as some poster has stated where he said that the float makes contact at the bottom and completes a circuit when oil level is low. Also, these senders are around $400.00 (US), which makes me think there is more to it than that.
I ran a simple test with a DVM and slid the float up and down and noticed that the resistance varies!!!??? Any light you can shed will help me resolve my oil level light flickering on and off intermittently.
I think I've found out how this oil level sender works, thanks to the link from Yamae, and a little experimentation. The float has a collar or bushing which is highly magnetised at the top (picture added showing the thin collar). I missed this magnetic effect since it is very localized and acts on the hidden reed switch inside the float guide (the brass/copper barrel), I missed this because I expected the magnet to be embedded inside the float at the end where the float runs up and down another bigger copper/barrel which also looks like it may have a switch inside it. As the oil level fluctuates, the rising and falling float, and therefore the magnetic field affects a spring inside the reed switch which either forces the contacts together or apart to either close or open the circuit, and thence illuminate the idiot light! Pretty neat, but is the whole thing justified for $400+???
I suspect that the heating/cooling cycle of the oil causes the solder to allow oil leakage into the reed switch space and cause it to malfunction intermittently. Will know for certain when I finally desloder the one I have out and take a looksee!!! Also, I think that the shape of the float (the two crescents at the ends, but note the lack of any magnetic collar!) is probably due to a one-size-fits-all approach, where the magnets can be added for models that have that option/specification.
Now you understood. You also need to know that there exists a temperature limit called "the Curie temperature" which is explained here below.
A magnets becomes not a magnet any more when it is heated up to the Curie temperature. Most of magnets become so at around 130 degrees C which is the high side of oil temperature. It simply means that you need a special magnet and a reed switch. Also an engine which experienced too much overheat tends to show this problem.
Thank you! I sort of vaguely remembered from my physics experiments back in my school years that heat destroyed a magnets properties, but never knew the effect had a name!! It's good to learn something new everyday, though!
Now all I need is a new float and reed switch to rebuild my Oil Level sender, unless the components cost $400! By the way, I salvaged a couple of these senders from the junkyard and one of them is toast, the other seems to be ok, but it is from a '94 and the total length from mounting base to the bottom of the float is different; also, the connector plug is different, although looking at it from the top (engine bay) you wouldn't think so! If anyone wants to see a side by side comparison of pre-'94 and '94, let me know and I will post a couple of pics.
You are most welcome, Yamae. I found some information on the following site about reed switches, but I think an EE like you would probably understand it better, since most of the info is compiled by engineers: http://reed-switch-info.com/
Here is a pic of the sender from a '94 and one from a '91 LS400. The difference is slight, but clearly visible - the one with the grey connector socket is from the '94 LS400.
Also, I think you should know that although removing the bolts (10mm) is easy once you get to them, actually taking the sender out is not very straightforward because of the double bends in the arm - you have to gently (I think the float can break easily!) go through several twists and turns while gently pulling it up and out!