1988 Eldo fuel tank swap
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HT4100 4.1, 4.5, 4.9 Discussion, 1988 Eldo fuel tank swap in Cadillac Engine Technical Discussion; Can the old fuel pump and float insert be saved removing it from a rusty tank. This eldo sat around ...
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    eldorick is offline Cadillac Owners Member
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    1988 Eldo fuel tank swap

    Can the old fuel pump and float insert be saved removing it from a rusty tank. This eldo sat around much of the last 16 years which took it's toll on the fuel tank but leaving the body in fantastic shape. It leaks fuel down to around 7 gallons. If careful, can I reuse the old sending unit while replacing the fuel tank, ring, and gasket, as a 1988 sending unit costs mucho bucks?

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    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
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    Re: 1988 Eldo fuel tank swap

    Quote Originally Posted by eldorick
    Can the old fuel pump and float insert be saved removing it from a rusty tank. This eldo sat around much of the last 16 years which took it's toll on the fuel tank but leaving the body in fantastic shape. It leaks fuel down to around 7 gallons. If careful, can I reuse the old sending unit while replacing the fuel tank, ring, and gasket, as a 1988 sending unit costs mucho bucks?
    Sure, you should be able to reuse it. The sending unit is a separate piece that fits into the top of the tank with a large o-ring sealing it. There is a cam ring that cams into place to hold the sending unit into the fitting in the top of the tank. There is a special tool to turn the cam ring but you can do it by tapping gently with a large screw driver and hammer to turn the cam ring. I would get a new rubber o-ring to seal it as the old one is likely to be hard and cracking from sitting. Also, pick up a new filter sock for the fuel pump pickup as it is likely to be covered with rust particles and/or dirt. At least clean the sock off....don't remove it and run without it. While the sending unit is out, check the rubber coupler that connects the pump to the sending unit. It may be getting old and cracking or swelling due to alcohol in the fuel... If the coupler is in good shape clamp it on both ends anyway with small screw clamps to prevent any problems with leaks or loss of pressure there. If the coupler is cracked then replace it with a piece of good quality fuel hose and clamps.

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    eldorick is offline Cadillac Owners Member
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    Re: 1988 Eldo fuel tank swap

    Thanks for the great info. I'll be taking on this project in the next few weeks. Would you replace the straps as they appear to have a fair amount of rust also?

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    Re: 1988 Eldo fuel tank swap

    Quote Originally Posted by eldorick
    Thanks for the great info. I'll be taking on this project in the next few weeks. Would you replace the straps as they appear to have a fair amount of rust also?
    Hard to say without seeing them. Inspect them carefully. If there is just surface rust then they are probably fine....but look at the ends where the corrosion will have a larger effect. If you are gettting a new tank and such then you might just want to replace them for piece of mind....

    Are you sure the leak is the tank corrosion...??... If the car sat and the o-ring at the sending unit dried out then it may be leaking at the sending unit fitting. The tanks are very well coated and protected from corrosion inside and out so a perforation due to corrosion is not very common.... It might be worth the exercise to drop the tank before buying bunch of parts and determine exactly what the problem is ... unless of course you can see the leak source and know positively what it is. If it is just fuel spilling from the top surface of the tank I would suspect a hose or sending unit 0-ring before I would think that the tank itself is leaking.

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    eldorick is offline Cadillac Owners Member
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    Re: 1988 Eldo fuel tank swap

    After purchasing the car last August, the first thing I did was put her up on a lift. I felt the top of the tank and a lot of heavy loose rust fell to the floor. At that point the outside of the tank was completely dry but had only 3 gallons of gas in it. After changing out all the other fluids, I gassed her up and noticed a strong smell of gas the next day with a decent sized spot on the driveway under the tank area. Incidentally, the fuel line running along the frame rail looks great. Do you think the ring or gasket could cause the leak overnight with about 10 gallons?

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    Re: 1988 Eldo fuel tank swap

    Quote Originally Posted by eldorick
    After purchasing the car last August, the first thing I did was put her up on a lift. I felt the top of the tank and a lot of heavy loose rust fell to the floor. At that point the outside of the tank was completely dry but had only 3 gallons of gas in it. After changing out all the other fluids, I gassed her up and noticed a strong smell of gas the next day with a decent sized spot on the driveway under the tank area. Incidentally, the fuel line running along the frame rail looks great. Do you think the ring or gasket could cause the leak overnight with about 10 gallons?

    Hard to say....how much leaked?? If there was a leak below the liquid level (as I suspect you are supposing...) then I would expect a steady drip-drip-drip. Overnight a large accumulation I would suspect. If the ring or gasket at the top was leaking it would only be splash leakage while you were driving but that would tend to drip down overnight from the top of the tank creating a small amount of "leakage" on the floor. That is why I kind of suspect the ring or gasket at the sending unit....that would make the top of the tank wet, you would have no idea how much leakage really occurred when you were driving and the only leakage evident would be the limited amount trapped on top of the tank when parked.

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    eldorick is offline Cadillac Owners Member
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    Re: 1988 Eldo fuel tank swap

    It makes good sense to drop the tank first as you mentioned rather than guessing. The only thing, doing this on a weekend will make buying a tank on saturday or sunday difficult but I could manage without until monday.

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