Gas Tank Cleaning Questions

mr bump

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I used por15 on my cs tank 5 years ago as a temp job, it's still in the car as I've had no issues what so ever. I've got a brand new tank to go in but that por15 has really done the job.
 

Paul Wegweiser

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Mother of cuss. Had to try to clean more. Anyone know where to get the resistance wire for the fuel sender? Or what gauge or size or metal it is?

I couldn’t find anything searching other than rigging to extend the connection.


Mike Self did a little research on this a few years ago (correct wire source, etc) , but finding that info might take some digging. I have been able to resurrect some pretty gross sending units with gentle use of solvents and scuff pads and PATIENCE. If the wire isn't broken, you may still be able to save the unit.
 

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JayWltrs

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Thanks, wire is broken-still surprised as I knew the risk and tried to be careful. It’s an easy fix if I can find something with correct resistence. Wire’s so fine it’s difficult to tell even whether it’s round or flat-it doesn’t roll in your hand easily and reflects light unequally. Need a jeweler loupe. But I’ve ordered a bundle of various round gauges and two flats that seem closest. Maybe I can crack this puzzle. Hopefully if I clip wires to test it will get close to the same reading as final soldering until I find the closest one. My fuel needle is jumpier than a methhead, so I probably needed to get in here anyway.
 

HB Chris

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Is your sender 245.5mm long? I have a sender from our 2800 that I think is 217.5mm but I need to check, later e3 and e9 have a deeper tank. Might be useable for parts?
 

JayWltrs

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Thank you, Chris. Mine’s a 74. So it’s at least 245 & Real OEM says 252, but I don’t know if that’s a real difference—not sure where they’re measuring from. Lots of zinc left, terminals cleaned up nicely and float moves easily. It should work fine after I fix the resistence wire, screen & new O-Ring. Thanks and I’ll holler if I’m wrong.
 

Paul Wegweiser

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Thank you, Chris. Mine’s a 74. So it’s at least 245 & Real OEM says 252, but I don’t know if that’s a real difference—not sure where they’re measuring from. Lots of zinc left, terminals cleaned up nicely and float moves easily. It should work fine after I fix the resistence wire, screen & new O-Ring. Thanks and I’ll holler if I’m wrong.


I checked quantity of the 252mm version and BMW has 29 of them remaining. I can get them for about $229.00, which (compared to the crazy $300-400 2002 ones), isn't **quite** so painful. There's ONE in the USA now. The others take about 7-10 days to obtain.

At least it's another option if you can't repair or secure a good used one. I'm away from my parts books, but can check alternate options later today. There's a nobility to restoring an original part, versus just writing a check for a new one, but for now - at least you have options.


Paul Wegweiser
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Maximillian Importing Co
[email protected]
 

JayWltrs

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Thanks. If you can find the wire mesh screen on the bottom of the sending unit for the CS that would be cool. Doesn’t appear to have a separate # in RealOEM & I don’t have an orange book. I think W&N has a plastic one for CSi. It’s the round thing at the bottom of the tank in the pic above. Here’s a better pic after much cleaning:

0AB4B3EC-8DAD-4FB8-A13A-77811964535B.jpeg
 

Paul Wegweiser

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I have never seen a wire / metal screen on one of these! NEAT! In my parts books (dated 1975) the mesh screen is not available individually. There are similar sending units on Benzes of that era - and perhaps Benz sells them separately. You might check classic Benz places. (SL Autohaus, etc).

I had to make a brass fuel pick-up screen for a 300SL (Gull Wing) a few years ago...with patience, ANYTHING can be done! It's my job to sell new parts, but I love seeing things restored and saved, instead of replaced!
 

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Mot27cars

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Mother of cuss. Had to try to clean more. Anyone know where to get the resistance wire for the fuel sender? Or what gauge or size or metal it is?

I couldn’t find anything searching other than rigging to extend the connection.
Is the wire gone?....or is it still there just not soldered to mounting point?
 
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Paul Wegweiser

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EDIT: the nylon / plastic version of the pick-up / sending unit screen is available using BMW Nr 16 12 1 106 983 from a 2002. ($20.59) Not 100% sure if this would have the same diameter as the 3.0 part, but I'd bet money on it. If I had the original metal version, I'd work on cleaning it and re-using it. A little carb dip goes a long way!
 

eriknetherlands

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Full should read 3 Ohms, empty should read 74 ohm.

Is that enough to calculate the wire resistance/cm?
I thought I had the ohms/length spec , but can't find it.

I did find this link, where roughly the same specs as above are mentioned, and an apparent successful repair with "22 gauge copper wire".

https://www.lesliewong.us/category/bmw/page/2/
 
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JayWltrs

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Full should read 3 Ohms, empty should read 74 ohm.

Is that enough to calculate the wire resistance/cm?
I thought I had the ohms/length spec , but can't find it.

I did find this link, where roughly the same specs as above are mentioned, and an apparent successful repair with "22 gauge copper wire".

https://www.lesliewong.us/category/bmw/page/2/

Those are the specs I’m using. Others suggest +/- 5 shouldn’t affect gauge function.

I read that link before & that’s my fallback. But the 22 gauge CU wire was used as a stub to extend the terminal, which I don’t love. 22 is too thick for the full wire length as it won’t properly lace the sliding terminals in the float and allow it to move freely. I’m betting original wire is closer to 40 gauge, but we shall see!
 

Ohmess

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Jay -- I think I have a used sender laying around somewhere if you want to go that route.
 

JayWltrs

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Jay -- I think I have a used sender laying around somewhere if you want to go that route.

Thanks, Chris. I might take you up on it if this doesn't work out. Of course, Tony probably has 40 of them stashed away here that I can try to pry away from him. :D

When I did my E3 resto, I came across this guy and his blogs. May be of help to you.
https://www.lesliewong.us/2009/07/26/bmw-fuel-sender-repair/

Thanks. For posterity, here's two very good threads, one w 40 ga wire using a resistor. https://e9coupe.com/forum/threads/72-bav-fuel-sender-shared-with-any-later-models.6805/

https://e9coupe.com/forum/threads/my-fuel-gauge-has-tourettes.4538/
 
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JayWltrs

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So, after trying different lengths and 2 different meters, I have:

40 AWG Nichrome 80 wire: 95-100 empty & 5-9 full.

38 AWG: 58-60 & 2.5-4

More fiddling required.

Odd discovery: Lots of cheap resistance wire out there because it is used in vaping.
 

Rek

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I used 3 ohm and 74 ohm but obviously did something wrong. Only the top part of my gauge now works, but the whole full to empty cycle is in that, so when the needle reads half empty, the low fuel light comes on.

It's on the list, but I can live with this for the moment.
 

JayWltrs

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I used 3 ohm and 74 ohm but obviously did something wrong. Only the top part of my gauge now works, but the whole full to empty cycle is in that, so when the needle reads half empty, the low fuel light comes on.

It's on the list, but I can live with this for the moment.

I'm also shooting for the 3 & 74, but seem to be hitting all around the target.
 
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