Fuel tank cleaning (car) tips or tricks?

[inphx]

Hey everyone,


I have a long-term project 1975 Cadillac Eldorado that’s been off the road for about 7-8 years. The fuel left in the tank has turned yellowish/light brown (classic old gas).


I’m planning to drop the tank, replace the sending unit, give it a proper clean, and coat the inside with POR-15.


A couple of specific questions:


Agitation step – For the cleaning phase, any good tricks with nuts/bolts or chain inside the tank? I’ve read the usual “shake/roll it” advice, but on a big Cadillac tank are there any methods that actually work well?

Shop option – A local radiator shop quoted me $240 to clean it, fix any leaks, and coat it with Marvel Mystery Oil. They don’t do POR-15. Since I’d have to reclean it myself anyway to remove the Marvel oil before applying POR-15, is it smarter to just do the whole cleaning + POR-15 job myself?

Also, is POR-15 (or a similar epoxy tank sealer) really the best way to future-proof these old steel tanks against modern ethanol-blended fuel, or is there something better these days?

 

[liliysdad]

Option 1 - New tank. It’s worth the cost to eliminate the hassle

Option 2 - Have it boiled at a radiator shop. This will reveal any pinholes and rust. Not as good as a new tank, but close.

The steel fuel lines will be as much of an issue as the tank. Maybe more.

 

[inphx]

new tank "unobtanium" for 1975 Eldorado.

Perhaps once i pull it and remove fuel sender i can determine if DIY or radiator shop is the pathway.

 

[yhprum]

It depends how diy you want to get. If you filled the tank with water and drain crystals (lye) it would probably lift the gunk and varnish. Once that’s gone you could use the citric acid method of rust removal posted here to get any rust. Then use a good tank liner.

 

[GRN96WS6]

I had this issue on my 90 Eclipse, impossible to get a tank in good shape, I found this process (vendors all over) but it was not cheap but worth it to me.

Welcome to Gas Tank Renu - Gas Tank Renu

www.gastankrenu.com

 

[gahrajmahal]

I used an Eastwood kit for my Avitar 68 Chrysler. My tank was in good shape and I just used swished the various chemicals around and dumped them out. The roof, or top of a tank is where your rust will be. Condensation from water in the gas.

 

[jeffberk]

Its a smaller tank on my '74Z but what I did was used this kit from Summit Racing and it seemed to help.

https://www.summitracing.com/parts/KCO-53000

I used the nuts and bolts trick to clean the tank while rotating it by hand. I cannot find it on the Internet but someone posted strapping his tank onto a rototiller and use it to spin their tank. It was hilarious to watch and likely overkill.

 

[PlanB]

I had a older motorcycle tank that PO had cleaned out and coated. The coating wasn't great (or even passsable) and nuts/bolts/chain were left in the tank.

Sorting that out diy was major time/energy ****. It was effort that should have been spent on a different part of the project.

 

[The Cobbler]

Mustie 1 on You Tube built a crude rotator to tumble tanks with nuts & bolts & whatever's inside .
He's used it a few times & it works pretty good

 

[Stuart in MN]

Auto City Classic in Minnesota sells gas tanks for Cadillacs but I didn't see any listed for Eldorados.

Can you tell if it's rusty, or just gummed up from old gas? If it's the latter you may be able to just flush it out with fresh gas and then change the filter a few times.

 

[inphx]

A complication is, while i was living in Texas decades ago I had a custom fab trailer hitch made.. its welded to the frame and has a unbolt-able design but this will be the first time i'm unbolting it. It encapsulates the tank. Otherwise dropping the tank and taking a peek would be easy peasy. No issues with leaks i know of but i want to do it right.

 

[BurtEggley]

Been there. Radiator shop to boil it out. Do not INTERNALLY paint or coat it. If it will be awhile until you use it, slosh some diesel in it round and round, drain that out and cap all the places air and critters can get in.

 

[racecougar]

 

[alwaysFlOoReD]

I have a cement mixer. And a tank that needs cleaning...

 

[ctandc72]

I had a older motorcycle tank that PO had cleaned out and coated. The coating wasn't great (or even passsable) and nuts/bolts/chain were left in the tank.

Sorting that out diy was major time/energy ****. It was effort that should have been spent on a different part of the project.

Could have been worse. You could have been in a shop (I was teenager) when someone decided to weld on an old steel motorcycle tank without any other precautions. "It's empty. It'll be fine." Needless to say - that guy wasn't working in that shop the next day.

 

[rust in the eye]

I deal with this semi frequently. Old yellow fuel doesn't equate to a rotten tank. You didn't mention any leaks
Once out and the sender removed yiou can get a good look. Might need nothing other a wash out.
Good luck.

 

[rust in the eye]

Gotta love farmers.

 

[ctandc72]

I deal with this semi frequently. Old yellow fuel doesn't equate to a rotten tank. You didn't mention any leaks
Once out and the sender removed yiou can get a good look. Might need nothing other a wash out.
Good luck.

This right here. Why not drain / pump out the fuel in the tank and use a cheap inspection camera to see what the inside actually looks like before going to all that trouble / $ to 'fix' something that might not need it?

Recently sold a vehicle that had been sitting for 4-5 years with 3/4 tank of gas. Pumped it out. It was old. It stunk. Heck, it barely burned - I used it in my burn barrel. Inside of the tank was perfectly fine. The grommet for the tank filler was rotted - but that's another thing entirely.

 

[ctandc72]

A complication is, while i was living in Texas decades ago I had a custom fab trailer hitch made.. its welded to the frame and has a unbolt-able design but this will be the first time i'm unbolting it. It encapsulates the tank. Otherwise dropping the tank and taking a peek would be easy peasy. No issues with leaks i know of but i want to do it right.

You have a white suit / hat to match? That's an epic Halloween setup.

 

[inphx]

Actually - i may have the hat. i would love some steer horns with a magnetic base as an occasional 'goof'.

 

[inphx]

I dont sell many cars... this one has been in my hands decades, coast to coast, NYC and Cali and silly stuff along the way.

 

[bamawildcat]

I'm going to jump on the "don't coat it" bandwagon. Steel doesn't rust with petroleum products in it, just the water that makes it in. Recommend getting it boiled out and any holes fixed at the radiator shop, then keep it topped off and use a good fuel stabilizer like Lucas.

 

[Stuart in MN]

I dont sell many cars... this one has been in my hands decades, coast to coast, NYC and Cali and silly stuff along the way.

A 1975 Eldorado had the 500ci engine, right? A friend had an Eldorado back in the day, it was like riding in a locomotive with all that torque.

 

[inphx]

Giddyup

 

[Mandres]

I have a cement mixer. And a tank that needs cleaning...

That's what I did. Strapped the diesel tank from our old tractor to my HF cement mixer and let er rip. It worked ok, would have been better if I could have slowed it down a little

 

[atch]

Giddyup

This doesn't have anything to do with anything. Just me not being able to keep my mouth shut. I have a friend who showhorned one of those 500 inch Caddy engines into a 1932 Ford roadster and got the hood (tops and sides) all on. His profession is restoring high-end cars so it looks like a factory put it in there; not a hose or wire out of place.

 

[inphx]

This right here. Why not drain / pump out the fuel in the tank and use a cheap inspection camera to see what the inside actually looks like before going to all that trouble / $ to 'fix' something that might not need it?

You were right, tank internals looked great to me. Got lucky.

I drained the remainder of fuel, fished out the old fuel sending unit sock rib cage and used a rag on a dowel for reachable areas and it seems good to me. This was the trailer hitch sub frame under the gas tank - heavy but nice to see the made in USA markings on the steel before i wire brushed the iron and freshened up. Reassembly went surprisingly quick with a combo of a harborfreight table lift for tank/frame and a two post lift for the car.

 

[inphx]

I deal with this semi frequently. Old yellow fuel doesn't equate to a rotten tank. You didn't mention any leaks
Once out and the sender removed yiou can get a good look. Might need nothing other a wash out.
Good luck.

Exactly. thanks!

 

[OldCarGuy]

Over the years I have purchasing a new replacement gasoline tank with success. If you can find a reliable source. I have gone the route of cleaning and coating tanks too, with success. The other option not mentions is having Renu clean then chemically bond the inside and outside of the tanks. That's often the best option.. Renu https://www.gastankrenu.com/


Here's some photo's of my 1976 Cadillac Coupe deVille. I purchased it new in 1975 and today it has 11,000 miles...




Massive 500 cubic inch engine

 

[vpd66]

I've used this fuel tank liner a couple times and have good results.
fueltankliner.html
It comes with all the cleaning and etching chemicals to do the proper installation.