Fuel Tank Slushing and Preparation

As a follow-up to Back to the Basics – Gasoline! (Under the Bonnet, Spring 1993), we thought it appropriate to offer a refresher on how to prep your car’s gas tank and apply sealing compound.

After reading the article, many customers expressed concern about the additives in modern gasoline breaking down or eating away at the coating. We followed up on your concerns and have been assured by our supplier that the white-colored sealer he has been providing us for several years is more than capable of with standing any current gasoline additives. We’ll keep you informed if there are any future developments.

To properly apply any sealer, the tank must be scrupulously clean Inside. In the past, this was easily achieved by simply taking the tank to a local radiator or engine machine shop and having it dipped. However, many shops today are turning away this type of work due to a variety of environmental issues. To allow you to properly, and safely, clean your gas tank at home we’ve recently added both a cleaning solution and an etching fluid which should be used together to properly prep your tank for sealing. Both of these products are biodegradable and can be safely used at home.

Most problems with gumming or sealer breakdown can be traced to improper preparation of the tank prior to the application, followed by improper application and draining of the sealer. Here’s how to do it the right way.

Getting Started

Before any work can begin, the tank must be completely removed from the car. It’s just not possible to properly clean the tank, or apply and drain the slushing compound without first removing the tank. Completely drain all gasoline and thoroughly ventilate the tank by allowing it to air out for several hours. Remove the sending unit, feed lines, and any drain plugs. Remove and replace, if necessary, any tank mounted fuel filters so they won’t clog. Now is also the time to remove any rust or scale from the outside of the tank using a suitable wire brush.


To prepare the tank for etching-arid slushing, we recommend cleaning it thoroughly with our biodegradable cleaning fluid, #220-620. This heavy-duty cleaning solution, supplied in gallon jugs, is also suitable for cleaning engines and other non-absorbent surfaces in the shop and home. Following the directions, use hot water to dilute the solution and slosh it inside the tank in an agitating motion. Drain and repeat as needed until all gum and shellac residue is removed. For very gummy tanks, plug all outlets and allow the solution to sit in the tank, covering the worst areas, for 24 hours. If rust flakes or scale are present, a length of chain can be sloshed around inside the tank with the cleaner, to loosen it up. Our sealer will fill only the slightest pin holes; anything more serious should be considered cause for one of our replacement steel, aluminum, or stain less tanks.

Etching & Sealing

Next, the tank should be etched to provide a good surface for the sealer to adhere. Using our etching solution, #220-630, plug all drains and pour the entire contents in the tank. Slosh it around, covering the entire inside of the tank and let stand for thirty minutes. Repeat the sloshing and let the tank stand for one hour. Drain the tank completely and allow it to air dry thoroughly; overnight is best.

The end is in sight! Now you’re ready to apply our sealing compound, #220-450.

Following the directions on the can, plug all drains and pour the entire contents into the tank from the filler neck. Using a back and forth and twisting motion, coat all inside surfaces thoroughly until a thin film is present. Now remove any drain plugs and allow the remaining scaler to thoroughly drain back into the can. Blow compressed air through fuel outlet before flushing compound has a chance to dry and clog fuel pick up! This is particularly important as some applications have a filter screen over the fuel pickup pipe. If anything more than a thin film is applied, the sealer will form a skin over the collected area (usually around baffles) and never completely dry. Alter a period of time, it will start to break down and clog fuel lines. This is probably the most common problem we hear about, so be sure and drain the sealer completely off. If thicker coverage is required, then allow the sealer to set up for at least 48 hours before reapplying another coat.

The tank should then be left to dry for at least another 48 hours before reinstalling it in the car. Be sure and replace cracked filler-neck hoses and the sending unit gasket if used. All plugs should be reinstalled using thread tape.

You will likely have more than hall of the sealer left over, which you can reseal and use again the next time you want to do the job.

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