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Is there a way to test the tank mounted fuel sending unit, electrically, to make sure it's working properly? It's for a Manta if that makes any difference...

Also, the Cork Float appears to have lost the varnish coating. Will this cause it to become "fuel logged" and sink? Can these be resealed? If so, what with. What about making a new one... Anybody been successful.....

All suggestions appreciated!
Paul Crane
75 Manta (original owner)
 

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I've remove them from the tank, and let them dry out...it's interesting to weigh them 'before and after' due to the fuel saturation, they get very heavy and give a false (low) reading. They can be 'bench' tested by moving the float through the range of motion (with the key on), and having someone check the gauge out from inside the car. I don't, however, know the resistance values the sender is supposed to have.

The contacts tend to corrode badly, and I usually separate the two halves of the sender, and polish the windings lightly with fine scotchbrite, then bend the copper contact tab to increase tension on the windings. This has worked well for me on all the cars I've owned. The gauge is far more consistent.

For the float, I've had pretty good luck sealing the float with marine epoxy (I use West System), but be aware the float will be a bit heavier than normal. So I bend the float rod to compensate. I did try once to make a float from brass, but to be honest it was a pain in the ass, although it did work. The tough part was determining the buoyancy compared to the cork, and adjusting for it.

Bob
 

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Discussion Starter #3
This a complete car disassembly, so I can't test it with the car's electrical system. I have two units and just need a way to test them so I can use the one that works the best. Maybe they both work...?

How did you separate the sender into Halves? It seems this cleaning method you describe would be the route I'd need to take.

Bob, How much did you have to bend the float? Guess its trial and error on the amount?

Anyone have any extra floats?

Has anyone tried a float from another brand of car?

Thanks
Paul
 

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resistance

The correct resistance for an Opel fuel sending unit is the same as for most other GM products, that is 0 ohms at empty and 90 ohms at full.

The reason most fuel sending units "fail" is their long term non-use. The copper contacts in the sending unit rheostat like to be moving and they corrode when they are left at a particular "spot" for a long time. Typically this is in terms of years and affects your "barn fresh" cars the most. Also cars without their charcoal filter or gas cap fare worse due to the moisture allowed to get into the gas tank. (Finally a reason to keep the charcoal filter?)

Both of RallyBob's suggestions are right on the mark (as usual) with regards to the scotchbrite and adjusting the contact pressure. The West System marine epoxy works great, and in fact I have seen whole motorcycle gas tanks made out of it! Another common marine fix is the commonly available styrofoam floats for marine fuel tanks. Some Walmarts even carry them for under $10.

http://la.znet.com/~r1937/Fuel.htm

has a decent picture to help explain how the gage works, hope it helps.
 

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epoxy

Any marina should have it on hand, or if not, any boat dealer or supply should should be able to order it. Because it works so well for so many things, some body shops keep it on hand too.

If you are going to use it on the cork, be sure to let it dry out thoroughly in the sun for a day or more if possible to completely dry out. Otherwise you will end up sealing the fuel into the cork and just making it heavier than it is now.
 

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Opeler
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Ascona fuel sending unit question

In testing the fuel gauge by disconnecting the wire from the tank, I decided to see if there was any voltage going to the unit. I found with my probe that the voltage is pulsing, and less than 12 volts. Other than that, the fuel gauge responded to grounding the wire to sending unit with showing full and disconnecting the wire showing empty. Connected, it showed just above empty. I know I have to take out the sending unit and clean it as described earlier, but I was surprised by the pulsing voltage. Shouldn't the voltage be constant?
Gerry
 

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The pulsing voltage is due to the archaic technology of the dash's voltage stabilizer. It employs a thin metal leaf spring heated by a very thin coil wire wrapped around it. The heat of the coil heats the metal spring, which extracts and disconnects the voltage, when disconnected it cools off a bit, thus contracts again and recloses the circuit, and this goes on infinetely. The gauge has such a slow responce that this pulse seems like a constant voltage to it...

Or I think that it works that way, correct me if I am wrong please...

HTH

I posted a pic to show the inside of the unit, not very clear but you can get an idea
 

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The pulsing voltage is due to the archaic technology of the dash's voltage stabilizer. It employs a thin metal leaf spring heated by a very thin coil wire wrapped around it. The heat of the coil heats the metal spring, which extracts and disconnects the voltage, when disconnected it cools off a bit, thus contracts again and recloses the circuit, and this goes on infinitely. The gauge has such a slow response that this pulse seems like a constant voltage to it...

Or I think that it works that way, correct me if I am wrong please...

HTH

. . .
Your description of the voltage stabilizer function is 'spot on'!
 

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Opelizer
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Fuel Tank Sending Unit Question

I just removed the fuel tank from my GT during the restoration process. Since the tank will be out of the car for quite a while, is there anything I should do with the sending unit to ensure that it will work properly when it is re-installed?

Rick
 

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"Search" first . . .

I just removed the fuel tank from my GT during the restoration process. Since the tank will be out of the car for quite a while, is there anything I should do with the sending unit to ensure that it will work properly when it is re-installed?

Rick
. . . first thing to do is use "Search", fuel senders have been covered in numerous threads like this one where yours was merged . . .
 

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Opelizer
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The merged link diverted my original question onto a different subject. I do not have a problem with voltage, and I already checked other links.

I am trying to find out if I need to do something with it to ensure that it will work when it is re-installed. ie:

Cleaning - If so, how and with what?
Storage - any considerations?

etc.

Rick
 

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Spray-Clean ASAP

I just removed the fuel tank from my GT during the restoration process. Since the tank will be out of the car for quite a while, is there anything I should do with the sending unit to ensure that it will work properly when it is re-installed?

Rick
Yes, there is. I advise spraying it, exterior and interior, with a can of ordinary carburetor cleaner spray. (To reach the interior, direct the output of the thin red straw nozzle to the small hole on the side of the sender).

Wear gloves and work clothes, and have paper towels ready, as this can free up some unpleasant gunk. The goal, is to remove residual internal fuel gum deposits, to not only allow the internal float to move up and down freely, but to also prevent those deposits from hardening (caused by air exposure, while the sender is out of the car).

Beyond that, the sender can be disassembled, but the adviseability of doing that depends on its initial condition.
If there is significant corrosion, to the point that the small nut is fused to the base of the main shaft, then an attempt at disassembly may destroy the unit. If the nut can be turned and removed, so that the housing can can be safely removed, then the internal brass contact points can be accessed for careful cleaning with an abrasive.

If required, an Opel retailer offers a rebuilding service.
(This presumes the sender, is not too corroded to repair).
 

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BTW... if you stick the tube from the can of carb cleaner into the sending unit.... its best to it while the entire unit is covered with a clean lint free towel .AND USE SAFETY GOGGLES!!!! Unless.... you enjoy the taste of that stuff. LOL
I'm sure you know this, but I've seen and had a few bloopers in my day!!:ugh:
HTH
Joe
 

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Also store properly

It's also a good idea, to store the sending unit in a sturdy and snug-fitting box (like a shoebox, with crumpled newspapers around it). A sending unit left loose, or kept in a box with other parts, has its housing can easily dented, which would interfere with or prevent future float operation.
 

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Vendor
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While on the subject...

I have two Manta fuel tanks being refurbished currently - one is a '75 EFI tank and the other is from an earlier model. Am I safe in assuming there are no differences between the two sending units?

Todd K.
PS - Hope everyone has a safe and prosperous 2008!
 

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Dude;
Wrong, the 75 tank uses a different sender, plus it's in a different spot on the tank
 

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Dang...
OK, what's the difference in the two? My early Manta tank is being altered to match the '75 and the sender will be placed in a similar spot (with similar baffling inside).
Any suggestions?

Todd K.
 

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Dang...
OK, what's the difference in the two? My early Manta tank is being altered to match the '75 and the sender will be placed in a similar spot (with similar baffling inside).
Any suggestions?

Todd K.
The 71-74 tank has the sender on the passenger side, and has a smaller outlet for the fuel. The 75 tank has the sender on the driver's side, and the fuel outlet is much larger to handle the volume of the EFI hi-pressure pump
 
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