Oil Light Coming On 91 Ls400?

[_mach_]

I got my 91 LS400 put back together but the oil light is flickering on and off. Let me attempt to describe the situation.

I start the car, and it idles just fine, no oil light (oil light will not come on if I do not rev the engine, it idled for about 25 minutes yesterday while i was filling it up with coolant), if I then rev it up a little, when the RPMs come back down the light flickers on....I then rev it up and the light goes off, but when the RPM's settle again it flickers on and stays on. It's like the oil light will not come on until I rev it up, and then it stays on at a higher RPM (higher than idle) but turns off when I rev it....This pattern repeats itself until the oil light stays on for any RPM under about 2500. I can put it in neutral and turn the car off, then back on, and the light goes back off for the first few minutes and the pattern starts over. It's like i am re-setting the electrical system.....This leads me to believe it is an electrical problem, because i will only kill the engine for about 1 second. The Cam seal was blown out, and spewing oil prior to replacement, so I know I have oil pressure (i replaced the seals), also the engine is very quiet and smooth. I guess my question is, has anyone ever had a similar problem, and is there a way to check the Oil pressure sending unit? It is the Red oil light in the middle of the Tach/Speedo, not the orange one below...not sure if that makes any difference, but I noticed 2 oil lights. Any suggestions are much appreciated.

Grayson

[curiousB]

As you say it probably is electrical and most likely the sensor gone bad. You should check for obvious stuff such as loose or corroded connector on the sensor. Failing that it might just be easier to replace the sensor than spend countless time debugging it. I don't think they are that expensive.

[oldskewel]

I got my 91 LS400 put back together but the oil light is flickering on and off.

...

It is the Red oil light in the middle of the Tach/Speedo, not the orange one below...not sure if that makes any difference, but I noticed 2 oil lights. ...

Those two oil-warning lights are very different. The red one is a traditional low-pressure warning. The orange one below is actually a low-oil-level warning! Pretty rare item on a car. My Porsche 911 has one (a gauge actually, not a light), but that's because the oil is so important in an air cooled car like that.

I don't know how the actual oil-level sensing is done, but I can confirm that at least on my '91 it is perfectly accurate. While driving a couple of months ago, I saw that light flash on just once, for about a second. Never saw it again. Checked oil level after I stopped, and it looked OK (but car was warm, etc. so the dipstick test was not accurate). Next morning, after sitting cold, I checked the dipstick again and it was *exactly* on the low mark. So I'll optimistically infer that the warning light comes on exactly when the oil level drops below an amount that corresponds to the low-mark on the dipstick. I added a quart and have been fine since, but was happy to learn that the car had this accurate extra warning system.

And regarding your problem, I concur with curiousB's comment.

Good luck.

[wuzzy1]

I got my 91 LS400 put back together but the oil light is flickering on and off.

...

It is the Red oil light in the middle of the Tach/Speedo, not the orange one below...not sure if that makes any difference, but I noticed 2 oil lights. ...

Those two oil-warning lights are very different. The red one is a traditional low-pressure warning. The orange one below is actually a low-oil-level warning! Pretty rare item on a car. My Porsche 911 has one (a gauge actually, not a light), but that's because the oil is so important in an air cooled car like that.

I don't know how the actual oil-level sensing is done, but I can confirm that at least on my '91 it is perfectly accurate. While driving a couple of months ago, I saw that light flash on just once, for about a second. Never saw it again. Checked oil level after I stopped, and it looked OK (but car was warm, etc. so the dipstick test was not accurate). Next morning, after sitting cold, I checked the dipstick again and it was *exactly* on the low mark. So I'll optimistically infer that the warning light comes on exactly when the oil level drops below an amount that corresponds to the low-mark on the dipstick. I added a quart and have been fine since, but was happy to learn that the car had this accurate extra warning system.

And regarding your problem, I concur with curiousB's comment.

Good luck.

Greetings Oldshewel,

Could be a myriad of things from a faulty oil filter, sending unit, electrical...but the main thing is...DON'T DRIVE IT IF THE OIL LIGHT IS ON!

You'll be sorry!

[_mach_]

Greetings Oldshewel,

Could be a myriad of things from a faulty oil filter, sending unit, electrical...but the main thing is...DON'T DRIVE IT IF THE OIL LIGHT IS ON!

You'll be sorry!

Thanks for that..... I'll know what's going on with it in the AM, I am going to put a mechanical oil pressure gauge on it to determine if that's the problem.

[fsuguy]

mach,

I just had my timing belt, water pump, cam seals, rotor and distributor caps, plug wires, plugs, and valve cover seals replaced. The Toyota mechanic who did the work said that there was a very tiny leak by the oil level sensor. I did not think much of it, but now every now and then my oil level light (the orange one) lights up. I checked the oil level and it's fine, so I think the oil leak probably has messed up the connection to the sensor. Perhaps this may be your problem too(?)

Let us know what you find out.

Mike

[killerFatty]

Since its not the low oil level light, but the red one near the tach, you should be able to pull a code. Hopefully the code(s) will show what the problem sensor is. Check lexls.com for how to pull the codes. If you cant figure out what a code means, try googleing it, or asking on here.

[fsuguy]

This is an old thread, but it is germane, and will possibly help others with these old models. I did some investigating after my oil level light would intermittently come on at highway speeds over 70 or so, and then go off, even though the oil level was at the correct marker on the dipstick.  Turns out that there are two possible reasons this may occur:

1. The oil circuit is not allowing the oil back into the oil pan fast enough to allow the sensor to give a safe reading, or

2. The sensor itself is marginal (since it works off and on).

The sensor itself is a float type, and is different from Gen. I to Gen. II at least that I know of.  The differences are slight enough so that they will not interchange between the two models without some level of ingenuity.  Cost of new sensors are approximately $400.00 (yes, $400!!)  Note that this is the oil Level sensor, and is accessible on the upper side of the transmission housing after the PS pump has been removed.  Two 10mm bolts hold it in place, and even after these bolts are removed, some dexterity is required to get it out since the float arm has a couple of bends in it, and the float itself is pretty brittle and can break easily.  The sensor is some sort of proximity activated switch inside a brass tube along which the float rises and falls; the float has an embedded magnet and apparently works by activating the switch as it rises and falls inside the upper oil pan. P/N for the sensor: 89491-14070.

Now for the possible explanation as to why the sensor may be malfunctioning - the heat from the engine is transferred to the oil and over time, heat will eventually lower the magnet's effectiveness, or downright kill it.  There is a good physics explanation for this, but I forget it. Another reason could be that gunk buildup between the float and the post on which it slides may reduce its freedom to slide up and down.  A good reason to keep the oil changed periodically!  Now you know, if you have read this far.  Good luck and good night!!!

 

[sha4000]

Thanks for sharing this bit of info.