Need to clean out a 26 roadster gas tank which I cannot take out of car. There is about 2" of 17 year old "gas". It has been suggested I use a combination of Phosphoric & Hydrochloric (HCL) (muriatic) acids. Not sure of number of parts/parts but what is the plus or minus and effectiveness of such a mixture? I am sure not a chemist
Take off the sediment bulb and drain it out as best you can. You will need to take the tank out of the car to properly clean, derust, and coat the tank.
I'm assuming you are talking about 2 inches old gas and some varnish? Regardless, acids will have little effect on either. Drain or siphon any liquid,then try dissolving what's left with lacquer thinner. Let it sit awhile and probably rinse and repeat at least once.
Acids can be used to remove rust but you might be better off using a commercial product like PQR15 or metal rescue which is less likely to damage other parts of your car.
It would certainly be easier to do a good job if you could figure out how to remove the tank.
Drain and then used a couple of gallons of lacquer thinner, let it sit but rock the car to slosh it around every so often. You may have to drain and repeat several times. I did this on a Model A, worked to some extent, but best is to drop tank and have cleaned and coated inside.
My go to is carb cleaner.Works great and is reusable .
Filling it with kerosene may help as well...
There's a toilet cleaner I've used to clean motorcycle gas tanks called "The Works." The advantage to a motorcycle tank is that you can swirl and swish it around but it should work the same even at rest. It does contain hydrochloric acid, so basically a thinned out naval jelly, but at a dollar a bottle it's hard to beat. My words of caution, keep a close eye on it, maybe even drain it every 15,20,30 minutes. If there's pin holes...the product will find them.
A oil-based solvent will work best.
Acetone, Toluene, etc.
I've used Berryman's Chemtool in old tanks before. It's sold as a gasoline additive (by the pint) these days, but smells like the carb cleaners we used to get in the "old days". Whatever's in it dissolves old lacquer, gas, peanut butter or anything else in there. Drain and flush with gasoline or alcohol afterward.
I've used Berryman's Chemtool in old tanks before, available at any good auto parts house. It's sold as a gasoline additive (by the pint) these days, but smells like the carb cleaners we used to get in the "old days". Whatever's in it dissolves old lacquer, gas, peanut butter or anything else in there. Drain and flush with gasoline or alcohol afterward.