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Discussion Starter · #1 ·
I just purchased a 1972 Opel GT that’s been in the garage for 31 years and the gas tank has a lot of gunk in the bottom from evaporated gasoline. What would you recommend to dissolve the gunk. It’s a great project car for my grandson and I but we need to get the gunk dissolved out of the bottom of the gas tank.
 

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Just Some Dude in Jersey
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You should buy a tank cleaning and lining kit and go through the process in the instructions. "Kreem" is a brand that has been around for a long time. I recently used a type sold by POR-15 that is made by a company called US Tank. The cleaners that come with it are the standard cleaner and metal prep that POR-15 sells. I use their cleaner/prep stuff for most of my restoring and rust removal. The "Degreaser" is a very effective acid that I use to take the rust off of parts. Soak parts overnight in the stuff and the next day all the rust is gone. You can re-use the cleaner/prep stuff after you pour it out of your tank for other projects. I used the liner/paint stuff that poured out to paint the outside of the tank. I like the Kreem stuff and have used it on 2 tanks and just recently used the POR-15 stuff on the tank for my present project car.

First, you have to rip the "sock" screen inside the tank off of the tank's outlet. You can get a super long pair of big needle nose pliers from Harbour Freight to help you do that. Then, close up all the tank openings, throw a handful of nuts and bolts in the tank, and pour in the Degreaser/cleaner, then you can take and old sheet and hang it from a tree branch or garage rafters to help you twist, flip, tumble, the tank to let the nuts and bolts scrub loose stuff in the tank, then pour it out. I put a T-shirt over a bucket to act as a filter and strain what comes out. Then I pour the now slightly used Degreaser back into it's jug for later re-use. Then you do the thing with the Metal Prep or go straight to the Liner step. Make sure the tank is dry(let it sit in the sun for a day or two) before adding the Liner stuff, then repeat the tumbling/twisting/flipping in the sheet and pour the excess back into the Liner can. After everything dries you then take a drill and clean out the vent holes and fuel outlet. You can remove the outlet and replace it with a larger diameter right angle AN fitting to improve fuel flow. Try not to get paint on where the fuel lever sender's 6 screws bolt to, the sender needs to ground through the tank and then to the body where the tank bolts to.

Here is a horrible picture of a tank I had lined by a professional shop to show you what the inside of the tank looks like and the stuff inside that needs coating. There's a baffle wall and a round thing we call the "spaquetti pot". The tank shown was apparently WAY to far gone to salvage and had catastrophic rust everywhere:

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If it is rusted out bad you might just want to buy a new tank. Also before you try to start it I would put some oil in each cylinder and let it sit.

Do you have any pictures of it?

Sam
 

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I had a local radiator shop clean and line my tank. They had to cut a "window" in it to fully get at what was in the tank that had been sitting for about 15+ years. The shop also pressure-tested both the radiator and the heater core, with the total cost coming to about $350. Years earlier, I had a shop do the same with my Triumph Spitfire. My personal view is that this is a job that is well worth paying someone to do.
 

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This isn't the only thread related to our fuel tanks and restoring them .
But maybe this is helpful to you
Good luck
 
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I shipped mine to Moyers at gas-tank.com to have them to open the tank, remove the sock, clean it inside and out, line the interior and coat the exterior. I’m quite pleased with the results.
 

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If there is any rust in the tank, send it to a professional.

If it is just varnish, and there is zero rust, you can clean it yourself. I bought a GT in 2016 or 17 that had been sitting since 74. It had about a half inch of varnish in the bottom of the tank, but no rust. I bought a gallon of acetone. Put half in, and let it sit to soften up the varnish. Dumped that into a 20 gallon barrel. Put in the other half gallon and a couple hundred 1/2 inch washers. Would swish it around every day, until I could see shine metal at the bottom of the tank. That was before I saw the very cool gyro reciprocating get up that Terry put together. Probably would have saved me a few days. But it wasn't like I would work on it all the time. Spent maybe 5 minutes a day swishing the washers and acetone around.

Ended up buying a second gallon of acetone to make sure it was really clean. Fished all the washers out with a magnet. Removed the sock, and just put an extra filter back by the tank. Even my fuel gauge started working after filling the tank with aviation fuel and some Techron.
 

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My tank had gunk in the bottom but only light surface rust. I cleaned it out in with acteone as LynnB suggested, however I used a few feet of "window sash" chain instead of washers. I chose this chain since the links are punched out from sheet metal and have square edges which I figured would do a better job of scrubbing. It's much easier to grab the chain and pull it back out when you're done. I also ripped out the fuel sock while I was in there. I did two or three rounds of dumping in a gallon of acetone with the chain and then doing the hokey-pokey in my driveway to agitate the chain throughout the tank (while my neighbors surely wondered why is that guy dancing with a metal tank?) After this, I thumped the sides of the tank methodically with a rubber mallet to further dislodge remaining residue and vacuumed it out. Finally, I poured in some Evapo-Rust to convert any remaining surface corrosion. I will note that this turned the inside of the tank a yellowish-green, which is apparently due to lead residue from old gasoline reacting with the product.

Before I did all this, I had problems with crud from the tank blocking my fuel filter. Ever since, everything has been fine.

Attached are some photos of various steps in the process.
 

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Discussion Starter · #9 ·
Thank you guys for all your help. Sam, I did put some Marvel mystery oil in each of the cylinders and I can turn the engine over freely from the fan. They solenoid would not engage when I hit the key for the first time but after tapping on the solenoid it freed right up and everything turns over Like it should. Thanks again for all the help about cleaning the gunk out of the tank
 

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Thank you guys for all your help. Sam, I did put some Marvel mystery oil in each of the cylinders and I can turn the engine over freely from the fan. They solenoid would not engage when I hit the key for the first time but after tapping on the solenoid it freed right up and everything turns over Like it should. Thanks again for all the help about cleaning the gunk out of the tank
Just wondering, does it run yet?
 

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Discussion Starter · #12 ·
Not yet. Unfortunately I have to go to work. I have a compression tester and I’ll test the compression next and continue working at cleaning out the gas tank. 31 years in a garage and absolutely no rust.
 

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one option is also a 5% citric acid mix with water and a couble of nuts and bolts, shake and rotate and leave for surface rust to get eaten away. then clean out with water, let it dry and then with alcohol. Then you can coat it or just run full tank of gasoline. I am always sceptical about coating inside of fuel tank.. if for some reason somewhere the coating won't stick well then it will clog the system and cause a headache.
 

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Not an Opel, but similarly my stepson’s E34 BMW came up from Virginia, but it sat for about a year prior. It ran at first then started stalling out randomly. Plugged fuel filter. Turns out the tank was FULL of residue from E10 gasoline that sat unused. Adding fresh fuel started to loosen it up and we went through 4 fuel filters before I finally dropped the tank and drained it. Shining a light inside showed a solid film of reddish/brown residue.

I got some clean gravel and a gallon of phosphoric acid, and sloshed that around for about 1/2 an hour. After draining and rinsing, the inside of the tank was spotlessly shiny inside. Problem solved.
 

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I'd vote for citric acid too. I would tie the tank on a concrete mixer and let it roll for an hour or two before rinsing it out. And if the time wasn't enough, repeat until the rust is gone. There is also an other big plus with citric acid, it's not harmful for the environment. I always buy it from an agricultural store(it's normally used as an additive in piglet food).
 

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Not yet. Unfortunately I have to go to work. I have a compression tester and I’ll test the compression next and continue working at cleaning out the gas tank. 31 years in a garage and absolutely no rust.
What we did on my GT we hook up a lawn mower gas tank and zip-tie it to the windshield wipers.
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Citric acid is a bitter eco friendlier and safer to work with but takes more time than phosphoric. Phosphoric rust removers might make flakes so good clean up is a must afterwards. I wouldn't suggest going stronger than phosphoric because then we get into stuff that eat also the good metal...
 

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Just Some Dude in Jersey
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Vinegar dissolves rust also, don't know if it's effective against the varnish.

Why go off the beaten path? The nuts and bolts and whatever cleaner comes with the tank lining product you choose have been proven to work.
 

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ILLUMINATI
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one option is also a 5% citric acid mix with water and a couble of nuts and bolts, shake and rotate and leave for surface rust to get eaten away. then clean out with water, let it dry and then with alcohol. Then you can coat it or just run full tank of gasoline. I am always sceptical about coating inside of fuel tank.. if for some reason somewhere the coating won't stick well then it will clog the system and cause a headache.
Citric or Oxalic acid washes are good suggestions as Fe(II) or Fe(III) citrate and oxalate are soluble. Essentially you can dissolve the rust if you give the oxide enough time to convert. Phosphoric acid is not a good choice for cleaning as Iron Phosphate is hardly soluble in water. After most of the rust is removed a Phosphoric acid was will convert residual oxide (and a little bare metal) to an insoluble phosphate protecting the surface.

These are common methods used to prepare steel and iron for electroplating and other types of coating. They might be worth looking at.
 

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I just purchased a 1972 Opel GT that’s been in the garage for 31 years and the gas tank has a lot of gunk in the bottom from evaporated gasoline. What would you recommend to dissolve the gunk. It’s a great project car for my grandson and I but we need to get the gunk dissolved out of the bottom of the gas tank.
Probably the most simple method to remove rust, paint, varnish, crud, off the inside of my fuel tanks has been to use electrolysis. Remove the fuel level sender, plug off all holes, ( I just use black tape on vents and leave the fuel fill neck open, and crimp off a hose attached to the fuel outlet line) flush the tank out with water a couple of times, then fill it with water, add a cup of Arm and Hammer washing soda (NOT baking soda), put a piece of steel or rebar in the center of a PLASTIC funnel, make sure the steel will not fall thru the funnel or touch the sides or bottom of the tank, stick the funnel into the opening where the fuel level sender goes, attach the + end of a battery charger to the metal inside the funnel, and the - end of the charger to the tank. Turn the charger to "trickle" or the lowest amp setting, Watch the gunk bubble out around the funnel. Leave this set for a day or two and then flush out the tank a couple of times. When it is dry, it is now ready for the prep chemical and then the coating. Other than rinsing the tank, no lifting, shaking, or stuck fasteners in the tank. Plus this gets to every nick and grove in the tank. And yes, remove that stupid screen at the fuel outlet with the long forceps you can get at Harbor Freight. A tip for drying if you need it done quickly is to put your shop vac hose from the output side of your shop vac into the fuel level sender opening and use a rag to seal the hose to the opening and let it blow out the fuel fill neck. Obviously you should remove the shop vac from the vac trash canister and make sure your hose and filter is clean so you don't blow junk into the tank. (Ohio does not get see the sun very often we have to improvise.....)
 
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