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FAQs: What You Need To Know About 3 Steps to Seal An Old Tank with POR15

Almost all fuel tanks are dirty and have to be cleaned out before sealing. It is very difficult to see the dirt and contamination inside the tank, but it’s there. In English, we call this bad stuff “gum and varnish”, and it’s almost always invisible to the naked eye.

If you try to seal a tank without cleaning it first, the new coating will probably fail, because tank sealer won’t stick to gum and varnish. Here’s how to clean out a fuel tank:

POR15 Cleaner Degreaser1. Mix 1 quart of POR15 Cleaner Degreaser with 1 quart of very hot water and pour it into the tank. Gloves And Eye Protection Should Be Worn At All Times.

Shake the tank, then place it in a different position every 2 hours so the solution can cover all the inside of the tank. When all surfaces have been subjected to the cleaning solution, shake it again, then drain out the tank, rinse it with water, dump out the water and start all over again. The first time you drain the solution, it’ll be very dirty; after the second solution has been discarded, the tank should be clean.POR-15 Metal Prep

Rinse the tank out with fresh hot water, drain thoroughly, and pour in the full container of POR15 Metal Prep.


2. With the POR15 Metal Prep in the tank, again shake, then place the tank in different positions every half hour until the entire inside of the tank has been treated with the Metal Prep. Then rinse the tank thoroughly with hot water several times and drain it. In order to get the tank completely dry, you must blow warm air into it for a long time. No tank will dry out on the inside by itself. The only way to do this job is to use forced air.

Tanks Must Be Completely Bone Dry Inside Before Sealing. The Sealer Will Not Stick To A Slightly Damp Or Wet Tank. 

 POR15 Metal Prep After Clean

3. Pour in the entire can of POR15 Fuel Tank Sealer and “roll” the tank around so that the inside of the tank is completely coated. Then drain any excess for at least 30 minutes to ensure that the sealer has not “puddled” in the tank. After you’ve done this, pour the drained sealer back into the can, but Don’t Put The Lid Back On The Can Tightly Or It May Explode!

POR-15 Tank Sealer In POR15 Tank Sealer Out POR15 Tank Repair inside sealed tank
Pour POR-15 Tank Sealer In Drain Any Excess POR15 Tank Sealer - After

Leave the can open and it will harden overnight. Then throw it out the next day. Allow 96 hours for the sealer to fully dry in the tank. Air dry the tank in a well-ventilated area.

The process time can be improved by using a low pressure blower or hair dryer (low or no heat) and allowing it to circulate through one hole in tank and out another.

Rusty Tank Before POR15 por15 finished sealing tank
Rusty Old Tank Before Using POR15 Tank Sealer POR15 Tank Sealer  - After



por15 por patchIf you have small pinholes you would like to seal from the outside, you can use the POR-Patch. This acts as a filler that is impervious to fuels etc.

The best time to add patches on the outside of the tank if there are larger holes to fill, is when you have finished drying the tank after using POR15 Metal Prep, when the holes in the tank are too big to be sealed by the sealer alone.

Here’s how you do this: Brush/Spray the Metal Prep on the surface and rinse off. Once completely dry, paint the area where the hole is with POR15 Rust Preventive Paint, then place a piece of the POR15 Power Mesh reinforcing fabric into the paint. Now paint the mesh outward from the centre with more POR15. The next day or 5 hours later, paint it again. You have now sealed the tank from both the inside and the outside.

And remember, whenever you want to seal a tank, you must use POR15 Metal Prep on the inside and/or the outside, because the adhesion must be perfect. After the tank is sealed, wait at least 5 days before putting fuel into it.



Sometimes you will be asked how to seal a tank that was sealed years ago with some other sealer that has now failed. In this case, you must use our paint stripper (POR Strip) first to remove that old sealer, and a gallon of stripper should do it properly.

First, pour in about a quart of stripper and let it work on each inside surface. It may take 4 strippings to do the job completely. The old finish may come loose in chunks or pieces or strips, so a long tweezer-type tool is helpful for removal.

After the stripping job is done, the tank should be rinsed out with hot water and then cleaned with Cleaner Degreaser. This is not easy work, but it’s the only way to do the job right. People who follow our directions perfectly always get a perfect job.

Special care must be taken to make sure the sealer doesn’t clog up feeder lines or other tubes inside the tank, and the tank must be propped before drying so the sealer doesn’t “puddle” in places where it could cause problems.



Q: Who Uses Fuel Tank Sealer?

A: People who restore, rebuild, or repair cars, boats, or other vehicles; companies with fuel storage tanks; non-restoration people who have fuels tanks in need of repair.


Q: What Are Some Typical Problems Requiring Need Of Sealer?


1. Tanks may be very rusty inside due to years of non-use.

2. Tanks may have gunk or caked sludge inside, which must be removed and the tank walls must then be coated.

3. Tanks may have pinhole leaks or leaking seams.

4. Tanks may have a combination of the above.


Q: Can My Tank Be Treated Without Having To Remove It From My Car?

A: Usually not. Occasionally a tank will have a small leak on the bottom which can be treated without removal, but this is the exception. Proper fuel tank sealing almost always requires tank removal from the vehicle.


Q: You Claim The POR15 Fuel Tank Sealer Is “The Best Fuel Tank Sealer Money Can Buy”. Why Is It Better Than The Others?

A: It’s better because it seals pinholes and seams far better than any other sealer and has great intrinsic film strength, which the others do not have. Its film coating is non-porous, keeping moisture permanently away from metal, and in this way prevents future rusting. It is also ethanol resistant.


Q: Does Fuel Tank Sealer Contain “Rust Inhibitors” That Other Sealers Claim To Have?

A: Any chemical can be called a rust inhibitor, since practically all coatings will stop rust for a short period of time until they are destroyed by moisture or wear and tear. Some types of oil have been known to inhibit rust for a limited period of time too. But the only real way to stop rust permanently is to keep moisture away from metal with a non-porous coating that will get stronger as it is exposed to moisture. Only POR15 Fuel Tank Sealer does this, and that’s why it’s the best product.


Q: How Many Types Of Fuel Tank Sealer Are There?

A: There are two types of tank sealer, and they are similar to each other in basic structure:

1. PVC type sealer is similar to the adhesive used to seal PVC pipe as used in waste disposal lines, sewer lines, etc. This material is white in colour, coats well, but doesn’t fill holes or seams well because it has poor film strength and is essentially an adhesive rather than a coating. It is highly flammable and has strong ketone vapours which are dangerous to people with heart conditions.

2. PVC-type non-curing sealer is yellow in colour and will dissolve in gasoline containing alcohol and other additives, which makes it dangerous to use in ANY fuel tank. Adheres well but never loses its stickiness, and it can easily be scratched off with your fingernail. Contains highly hazardous ketone solvent M.E.K.


Q: Should I Always Use A Por15 Fuel Tank Sealer After Thoroughly Cleaning Out My Tank?

A: No. Fuel tank sealer should be used as a last resort, and is not always necessary. Fuel tanks that are rust-free and have no pinholes or leaks may not need sealing at all. They should, however, always be kept full of gasoline, which prevents condensation and further rusting. If vehicles are not used frequently, fuel tanks should be treated with Fuel Preservative/Stabilizer, which will keep fuel fresh for more than two years and insure quick starts even after months of non-use.


Q: Can Por15 Fuel Tank Sealer Be Re-Used?

A: No. Used Fuel Tank Sealer should be discarded because it absorbs moisture from the atmosphere during application and will not adhere properly a second time.


DANGER: Harmful Or Fatal If Swallowed Keep Out Of The Reach Of Children Contains Petroleum Distillate Combustible Use Only In Well Ventilated Areas.

Do Not Re-Use Sealer. Let drained sealer dry in open can, then discard in accordance with local regulations. Avoid breathing vapours directly from can. Avoid contact with eyes and skin. Use POR-15 Solvent or lacquer thinner to re-move sealer from skin, then wash with soap and water.

Stir Well Before Using. This Sealer Cannot Be Mixed With Any Fuels.

Mentioned Products:

- POR15 Cleaner Degreaser (was Marine Clean)

- POR15 Metal Prep (was Prep and Ready)

- POR15 Tank Sealer

- Or you can buy a complete Fuel Tank Repair Kit which includes all three steps that you need , depends on the size of your tank.

- POR15 Paint Stripper POR Strip

- POR Patch

- POR15 Power Mesh

- Fuel Preservative/Stabilizer