I have an original fuel tank that is in decent shape. Looking for feedback on a product to use to clean the inside of tank that will not harm engine/fuel tank/fuel lines. Appears to be a little varnish in a few areas inside the tank.

If the tank is in good shape inside,I used acetone and some crushed stone to swish it around with the sending unit removed.
Acetone does evaporate so act in a timely manner.
Rinse with water,use compressed air to dry or let air dry.
Other people may recommend a different method,but this worked for me and had no issues.
Hope this helps

I used a POR 15 kit in my 65s tank That was like 25 years ago.It was plain nasty and bad.Used it as per directuins and sealed it.Changed senders like 8 years ago and still looked new inside.Well worth the money.I did let it sit in the sun and dry before I used sealer.Then let it sit in the sun a day or so so it cured.Rocky

I had a nice original gas tank in my 1971 Barracuda, except for all of the varnish, gunk, ethanol residue, etc. throughout the tank. I gave up on cleaning and replaced it with a new Spectra tank. I saved the original in hope of one day being able to clean it....completely.

I would not put anything abrasive in the tank. The original tanks were made of terne plate steel. There is a lead-tin coating on the steel that was use to prevent corrosion. Don't damage the coating on your tank.

I would also avoid taking it to a radiator repair shop to have it hot-tanked. And stay away from muriatic acid. Both of these will damage the lead-tin coating.

David

Eastwood sells a cleaning/sealing system that is supposed to work pretty good, but it is not cheap.
I did one 30+ years ago by dumping in about 3 pounds of 1/4-3/8 nuts and bolts and swishing them around with acetone or something like it. That one wasn't so bad and it worked well.
The tank in my current car was replaced with a new one due to the amount of rust inside, not just residue.

[quote=gzig5].
I did one 30+ years ago by dumping in about 3 pounds of 1/4-3/8 nuts and bolts and swishing them around with acetone or something like it.

I used a decent size chain on my 48 DeSoto fuel tank. So far (about 20 years), no problems.

I took one to a machine shop and had them hot tank it.