Ron - 1. run an entirely new wire on the outside of the car and see what happens then

2. use a multimeter to measure the sender at different levels

3. remove the gauge and bench test it

Ron writes:
>>>It' kind of funny, everyone on this site states how unreliable the OLG is and to always you the dipstick (which makes total sense to me) <snip>.

I don't even have a dipstick, I only use the OLG - mine (other than a few glitches with that rivet) has been totally predictable so it's all I use. And I've done over 100 oil changes plus adding at least a quart or two in between each of those.

1) change oil, get OLG 'around' the middle warm/idling (I'm not that particular, just don't want it pegged either way.
2) watch it go down as the miles go up.
3) when it's at the bottom and doesn't come up; add oil like in step 1.

Chuck.H
'89 TurboLookTarga, 338k miles

Firstly,..what a great informative thread,..many thanks to all the contributors...

Epic fail with today's work on the oil level sender changeout...really had me going in circles....installed new one today and had the gauge show bottom...(WTF). The test for the instrumentation showed fine (a peg).

Inanycase,...I started with a gauge reading that was not quite like others but considered VERY useful to me (I don't know WHY I had to frick with it). When my oil level tank STICK shows mid-mark (and that's following ALL rules to properly check oil on a 911,..INCLUDING ensuring my front cooler lines are toasty AT the front cooler),..my oil level gauge would i9ndicate near max (not red). I understand the full range of the gauge is ~ one quart. SO: when she reads mid-scale (with parameters stated above), that would mean I'm one-half quart down in the tank,.....this has always proven to be the case (quantitatively). My intentions were to replace the 23 year old sender with a new one, hoping to see the classic mid scale guage reading MATCHING the mid stick level reading. My original setup was quite nice, but I had to be hard-headed and achieve parity through parts replacement...NOGO>

Now she doesn't read anything,..even after cleaning up the old one and reinstalling....WTF? Since I accomplished many other tasks today, I've called it a day, for now. There has to be something I've overlooked. I did not take any voltage readings but did get some ohmage readings between the new and old sender,..they were certainly different. (Has anyone measured the ohms readings on a brand new sender?).

I'll regroup for another session tomorrow...looks like this sender goes in in ONLY one direction (as mentioned),..so I don't "think" I've an issue there. My concern is the wiring integrity.

We'll see,..the old sender seems to go in easier than the new sender, yet they look identical....WTF?

I'd like to get some resistance measurements from any PP's on the full sweep of a new sender, should anyone have them..

Thanks to this thread, I'l disassemble (tabs) the old pup and clean her up properly and provide good contact tensions.

Tomorrow's another day.

Thanks to all!

Doyle

It may fit in better cause you are more familiar with how to jigger it in there. It was easier for me to put the same sender unit in after I had done it.

My problem I had was the gauge needle jumping to full after I re-did the wiring. I thought I screwed something up soldering or otherwise. But after taking a lunch break and restarting the car it measured perfectly. Don't know if the electricals just had to reset or what?

Is this your problem or is yours not reading at all? Elementary question, but did you remember to reconnect your battery?

Quite elementary.....Yeap battery connected.

I'll get back on this tomorrow AM early and report back.

I will say that my current resistance readings on the new sensor (top/bottom) is 190 ohms/3.1ohms. The original sensor presented a bit higher resistance #s for sure,..but I didn't document the resistance. My gauge needle is not moving, except during ground tests.

Tomorrow's another day,...

Thanks,

Doyle

Just to add to this well written thread, forgive me if this was already posted.
If you're replacing the level sender check your dipstick pt #. Early cars used a930-107-731-00 dipstick, this needs to be replaced with the 930-107-731-01 which is marked slightly lower and is calibrated to the later model sender.
Also always replace the aluminum washers, part # 900-025-003-30. DON'T USE STEEL WASHERS, they will allow the nuts to loosen up. As for tightening the nuts Draco was spot on with point 18.

Done ! Made adjustments to the new sender...my magic range was 0.4 ohms to 230 ohms.

Mid level on the oil level gauge is now dead nuts on with center mark of dip stick (my stick is the factory one so no worries there). I'll have to order fresh washers and install them later,..for now she's installed with the original ones that were there. All torqued everso slightly!! I hooked up a precision pot to the wires heading back to the gauge and found the gauge to be extremely incrementally smooth.

I cleaned up the old one (original from '89). The sweep was still quite smooth but the range was off a bit,..some tab bending of the stops allowed me to set it as I did the new one.....the old one still works but will be banished to the (functioning) old parts stock!!!!!!!!!! (retired).

Great thread here with all the information needed. Big thanks to all!

BEST!

Doyle

Sorry to bring this thread back, but I'm trying to troubleshoot my sender and the above is confusing to me. If the only thing connected to the sender is the DVM, how are you getting voltage readings? It seems to me the only things you could measure at the sender are resistance and continuity. But I'm no expert in electrical troubleshooting so maybe I'm missing something.

He is indeed measuring volts, but he has connected the DVM to the harness coming from the gauge (and not to the sender as you assume). The 7.71 volt is what the circuit in the gauge applies to the sender to measure the resistance.

- Manfred

Thanks Manfred, that makes more sense now that I realize what I'm looking at in the pics. What threw me is that his description is different - "connect Red lead to center connection on OLSU and Black lead to ground attached to one of the side bolts".

Connected as in the photos:

Ignition on, I get 8.5 volts.
Ignition off, I get 0 volts.

oops my bad :( glad yiu figured it, so you look good on the gauge readings.

Yeah, I'm convinced my problem is a bad sender. Thanks for your write-up! I was searching for info on how to troubleshoot the circuit, and this thread was just what I needed.

Muchas Gracias Draco.
 

Hey Draco just wanted to say thanks for the very helpful writeup. I finally took the plunge to repair mine after doing an oil change and didn't even have to look at your writeup since I'd pretty much memorized it from reading it a bunch of time.

My issue with the sender was simply the rivet holding down the center lead. I just used a well placed bolt and squeezed down on the rivet to expand it and make the external tab have solid contact once again.

Taking the sender out was a fun 'experience' but somehow putting it back in was a snap. I didn't even have to watch the video, it's a bit intuitive especially if you remember what you had to do to take it out in the first place.

The other fun bit was realizing that the cork seal goes in only one way. :rolleyes: felt like an idiot wondering why it didn't fit and was afraid to break it until I took a very close look at it. What can I say it was late at night and doing the repair was a spurt of the moment descision since I had the oil drained.

Even with cleaning everything out, freshening up the sender and getting rid of most of the crud accumulated on the side of the tank it was an hour and a half job and I finally have a working oil level gauge after a year and a half of ownership of my bad ass baby.

Por Nada Muchacho!

I am happy I could assist.

I need to service my gas tank sender unit (GTSU, soon to come to your local forum) :D

RSD,

Jim

So I just pulled my sending unit out and readjusted per this thread. When I tried to measure resitance on the Sending unit by putting attaching the ground to the unit bolt on face and the hot lead on the tab that is connected to the unit I get infinite resistivity. Does this mean my SU is toast?

I am not an EE, but I only measure for Voltage, to insure the circuit is not faulty.

As I remember my EE tutor's lesson, infinite could mean high resistance. To know for certain, you need to open her up.

The gas tank sending unit is a breeze compared to the oil level sender. I did mine three time before I realized that the reason the cylinder kept falling off was because the was a little nut and washer missing from the bottom my unit.

The result after every autocross the cylinder would plonk and get cockeyed preventing the float from moving up and down.

Jiggle the spade in the center, if it moves that could be the cause of your open loop indicating infinite resistance. If that's the case the unit is very salvageable.

My float maybe leaking and giving a false low reading, well will soon find out. had my gauges serviced at noho speedo but that is 90% my speedo was 10 miles low but they recalibrated it.

Just wanted to say this is a great write up.

Just replaced my sender which has never worked properly since I got the car in 2002.

Cleaned around the tank with simple green followed by a wash with Paint Thinner.

The biggest deal for me was seeing the old gasket crumble as I was removing it.

In the end, I decided to get a new sender but after looking at the old one, I can see how easy it would be to refurbish.