How to clean and seal gas tanks.

By Jim Ellis
Published: December 23, 2008

How to clean and seal gas tanks.

Have you done yours yet?

You may be getting around to this job sooner or later if you or the DPO has not yet done it. In my case the DPO had done a poor job of sealing the tanks, which resulted in making the job even harder for the current DO. Here is what I found and did:

Upon removing the tanks from my SV I found they had been sealed at some point in the past. At first I thought, “Oh joy! I can skip this and carry on with other parts of the project.” But no. The previous seal job was botched. The tank had not been cleaned well before sealing and the sealer was starting to come off.

So I now had to figure out how to remove the old sealer, clean the insides of the tanks, and get a sealing kit. For the sealing kit I went with Bill Hirsch. For cleaning I went to the hardware store and made a lucky mistake (see below). The Hirsch sealing kit was recommended to me by a fellow Alpine owner. I also did a search on the net and read good things about his product. So I placed an on-line order for just the sealer – my first mistake. Seems you need to buy the etch to ruff up the inside of the tanks so the sealer will bond. I found this out later and through a semi-complex deal, I combined with another Alpine buddy on etch and a cleaning product that Hirsch sells. About this time I found out the etch is phosphoric acid. Remember that, as it will come in to play later.

Now I needed to get the tanks ready by getting the old sealer out. The Hirsch instructions informed me that paint stripper might remove some forms of tank coatings so that is what I tried. Off I went to the hardware store and got a gallon of the stuff and poured about half in each tank. I used duct tape to cover the holes and just rotated the tanks every few minutes for a couple hours. Then I emptied the mess out into a bucket and washed the tanks out with water. Lots of sealer came out but upon inspection I saw that much was left inside, hanging in strips and stuck to the walls of the tanks. Hmmmm now what…  I was thinking the paint stripper was still ok, so I put it back in the tanks and repeated the whole thing. Once more, lots came out but much was still left in the tanks. Ok, now I was getting mad….  I poured the stripper back in and left it for several days, rotating the tanks every now and again. This time I figured they would be clean as a whistle, but no, still there was old sealer in the tanks. So out came the steam cleaner and I blasted the things with water hot enough to cook a turkey. Still there was sealer in the darn things. Next I tried dumping in some Purple Stuff and a bunch of rocks from the driveway shook the tanks for all I’m worth. This worked to some degree and more sealer and some old paint came out. Finally I decided they were clean enough to use the etch. So I dumped it in and rotated the tanks, sure now that when I was done it would be ready to seal. I was counting on the etch to remove the last of the old sealer and paint. But while the etch did do something, the tanks were still not how I thought they should be. Since I had split the sealer and etch with another fellow I was getting worried because at this rate I will have no etch left. So off to the hardware store I went to buy more acid. Looking around the store I saw no phosphoric acid. I asked and was given a gallon jug – total cost under $5. Now, Mr. Hirsch gets a whole lot more for a whole lot less of this stuff. I could slosh this stuff in the tanks like there was no tomorrow. I went back to the shop to have another go at it when I noticed that this was not phosphoric acid, it was muriatic acid (hydrochloric acid). I dumped it in anyway… rotated the tanks every few minutes for an hour or so, dumped the acid back in the jug, and rinsed the tanks in cold water. Right away I noticed a difference. This stuff has bite. Not only did it clean the inside of the tanks but if you spill it on the concrete it cleans it too. Still the tanks were not good enough, so I gave it one more go with the muriatic acid. This time they looked great: as if they were bead blasted on the inside – all I could ask for and more.

This is the point where I made a mistake. I left my tanks to dry and they rusted. What I should have done was pour the etch in the tanks as soon as I washed the wrong acid out. The correct etch causes some sort of chemical reaction and leaves a whitish coating in the tanks that does not rust. When I found my tanks had a nice coat of rust I was heart broken, but since I had the muriatic acid and knew it would make short work of rust, I dumped it in and sloshed it around for a bit. I followed up with a rinse and shot of compressed air. Then I dumped the correct etching acid in and sloshed it around for an hour. Now I was golden. The insides of the tanks were almost too pretty to seal.

At this point you need to let the tanks dry completely – as in bone dry – before dumping in the sealer. I waited a few days and then poured it in. One thing about the sealer is that it is thick and you will need a good bit of it to have enough to coat the tanks. I bought a quart plus one pint and when I was done had a full quart to forward on to my cohort. I think if you are doing one set of tanks a quart will be enough but a pint might be too little. The final step was easy. Just rotate the tanks with the sealer inside and get a good coat. Do not get in a hurry. Spin them around slowly and the final product will be lovely coated tanks and no more paint chips in the fuel line.

In summing this up, the real job is getting the insides of the tanks clean. I was very happy with how the muriatic acid worked and I think it was a lucky mistake that I tried it. I can tell you it is nasty and burns if you get it on you and you must wear safety glasses. I have also been informed by some well respected know-it-alls that it will eat metal so I would suggest you do not leave it in the tanks for any extended length of time. Also the phosphoric acid leaves a nice rough surface that does not rust. It is what the makers of the sealer suggest you use to give the sealer a surface to stick to. Finally you want to save any left over acid or sealer. I just dumped it back in the containers it came in. You certainly do not want to dump it on the ground or down the drain.

There you have it! A back yard tank clean and sealing.