How to Deal with Rust in your Motorcycle Gas Tank...
Rust in your Gas Tank?
Rust can occur on the inside of any metal gas tank that
is not kept full of fuel all the time, especially while
parked or stored for extended periods of time. The rust is
primarily caused by the oxidation of the metal from water
occurring in the form of condensation from the air within the
tank, and is more likely to occur in high humidity
locations (such as the coastal states) than in very dry
locations (such as deserts).
This is a sure sign that there is rust in your fuel
tank that needs to be addressed (image of carb float bowl with rust
residue from a KR member's carb jet-kit installation instructions --
I annotated the image with the text):
1. How to prevent in-tank rust before it occurs:
- Corrective Action:
Fill gas tank to maximum to displace any air any time the
bike will sit for more a day or two. Make it a habit to take
on enough gas to top off your tank as your last stop before
returning home from rides. If the bike will be stored or
parked without running for more than 6 weeks, place a fuel
stabilizer into the tank before filling it to the rim. If
bike will be parked or stored for more than 3 months, drain
a half-cup of fuel from the bottom of the tank (or enough
to remove any standing water), and top off the top of the
tank with the required amount of fresh gasoline every 3
months to keep it full. If bike will be parked or stored
for more than 11 months, drain tank completely and air dry,
then place silicate packets inside and seal tank at all openings against
2. How to remove surface rust:
Interior of tank has surface rust, or heavy rust.
- Probable Cause:
Tank or entire motorcycle was stored or parked for a period
of time with less than the maximum amount of fuel in the
tank (possibly stored with tank empty).
- Corrective Action "A" (Wet Sanding, aka The Old School Method):
The old school way of doing a rust removal was to remove
and drain the tank, remove the plumbing (fuel sender, fuel
selector valve, etc), then add a quart of distilled water
and a quart of pure sand or fine gravel. Shake for a while,
rotating. This will actually sand out the surface rust.
Rinse out, and repeat sand-shake-rinse procedure if
necessary. Then use a higher-abrasive material (such as
quartz dust or BB's) to repeat the procedure yet again if
required. Rinse repeatedly with a garden hose, then again
with distilled water, and finally with gasoline. You should
use this method if you actually have any flaking rust
before proceeding with any other method, to remove the
flaking and expose the metal underneath.
Reinspect tank's interior. If any rust remains, utilize the
solution mentioned below in step 2(C) OR 2(B). If no rust remains,
change your fuel filter (replacing it with one with a paper
element), and then change the filter again after about a
week of riding with the factory-specified fuel filter
(sooner if you didn't rinse properly and get all the sand
out, as the paper filter will become clogged).
Note that not all fuel filters
are the same, and some are more appropriate for use after
this procedure than others. Specifically, many OEM stock
fuel filters contain a metal screen mesh and magnet
combination, and while this is good for picking up extra
rust that may come from the tank, it is not good for
picking up fine bits of sand. Thus we recommend using a
paper-based fuel filter at first, to ensure you capture any
excess sand from the process.
For those who appreciate such
things (as I do), it is quite feasible to install dual fuel
filters inline in your fuel hoses on many bikes -- one paper element
filter and one magnetic/screen OEM filter.
- Corrective Action "B" (Chemical Sanding/Rust Removal):
The new school way of doing a light rust removal is chemically,
via Yamaha's Fuel Tank Rust Remover ($14.95, Part Number
ACC-FUELT-CD-KT). It's a two part kit, with part A being a
pint of phosphoric acid and part B being a sodium
metasilicate solution (absorbs any remaining acid and dries
out the interior). To use, you remove & drain the tank,
seal the bottom openings, then fill it half way with water.
Add the phosphoric acid and top off the tank with more
water. Cap and seal, agitate. Remove cap (to vent), and let
sit for four hours (their recommendation -- I'd visually check before
draining as you may need as much as 24 hours). Drain, rinse (a pressure washer is
recommended), repeat drain & rinse operations several times
(hey, we're talking about an acid here!). Then pour in part
B, and agitate to coat every nook and cranny. This will
absorb any remaining moisture and any remaining acid. Drain
and allow the tank to air-dry completely.
Note that this general
process conversion is a part of POR-15's conversion/sealing process
(listed below) and does not require purchase of Yamaha's kit if you
are going with Corrective Action "C" (below).
- Corrective Action "C" (Chemical Sanding/Rust Removal, plus a hard surface sealant):
Utilize a rust-remover or kit including a rust-remover & stripper such as
15 to remove the rust, and then coat with the same
firm's coating material (since the products are designed to
work together). No sanding necessary! POR-15's coating is an epoxy-like two-part thin-coat material
that is hard as a rock (and is humidity-cured, so it cures better/faster the higher the humidity level). Allow to dry for the specified period of
time (or longer) before reinstalling tank. Change your fuel
filter when reinstalling tank. Use tank as usual.
Note that POR-15 kit listed above also contains a stripper specifically designed
to remove Kreem and/or RedKoat tank liners, if you've gone that route
before and run into problems. They also offer a cheaper kit that doesn't
include a stripper for previous coatings. Also note that the POR-15 route
will typically take about 4 to 7 days to do it's magic (all the steps, plus curing) for
a heavily rusted tank -- it's not a fast process.
Metal converters use a
chemical-based conversion process that converts iron rust
(iron oxide) to a new metal (usually magnetite, a very hard
form of iron oxide that is chemically inert and therefore
not prone to rust).
Rust strippers use a chemical-based acid process that removes
rust (turns it into loose particles to be washed out), and is
normally followed by an application of a specific acid-neutralizer
or a combination acid neutralizer + surface-prep agent (as a single
- Corrective Action "D" (seal/coat - latex barrier sealant):
Use Kreem or RedKoat to seal the tank, which coats the
interior of the tank with a thick latex or latex-like
substance. If you use this method, you need to use Corrective
Action "A" or "B" first to remove the surface rust! Many
users have used Kreem or RedKoat to their satisfaction, but
a lot of users have also complained about the product
breaking down after a number of months or years, flaking
off and clogging the fuel system & carbs (esp. in hot-weather climates). As a result, I
don't tend to recommend either these two products, but with
proper surface preparation, they should work.
Note that the POR-15 kit (Corrective Action "C") comes with an acid
stripper that will specifically strip away Kreem and
RedKoat linings if you are having flaking issues using one of these
- Corrective Action "E" (Electrolytic Rust Removal - aka reverse plating process):
There is a simple way of forcing the rust to plate a sacrificial
electrode (steel or iron), but the process can take quite some time.
Needed are a battery charger (a weak one will do) or other
power-source (an old step-down power brick for an discarded
electrical device will work if you slap a couple alligator clips on
the leads), a piece of bare mild steel or iron as large as you can
find that will still fit through the gas-cap opening without
touching anything, water and washing soda (Arm & Hammer brand will
Remove the fuel-tank sender assembly, the petcock, the gas cap assembly, and any other removable
items from the gas tank. Seal up all the holes in the tank except the gas cap filler hole (using plastic
or rubber -- do not use aluminum), so that it's water-tight.
Mix 1 Tablespoon of washing soda per gallon of water and fill the
tank with the mixture (note: stronger will not accelerate the
process, so don't go overboard).
Without plugging it into the wall, connect the battery charger or
other power source as follows: positive to the mild steel or iron
part, and the ground to the gas tank itself (such as to a screw that
normally holds in the petcock). You need to make sure that the lead
to the mild steel or iron part will not touch the tank's metal, so
insulated wiring is smart.
Figure out how to support the steel or iron part in the tank without
touching the sides or bottom, and without forming a grounding
circuit to the body of the tank (a bit of nylon mesh attached to a
plastic ring too large to pass through the opening of the tank will
work wonderfully -- or some nylon twine tied off to something above
the tank). Lower the metal into the tank and double check that it's
not touching anything except the solution.
Now you're ready to energize the system -- plug in the charger. How
long the process will take will vary with three factors: the amount
of surface area of the metal piece being suspended into the
solution, the amount of power running through the solution, and how
much rust we're dealing with here. In particularly bad cases, you
may have to drain/rinse out the tank every 12 hours, wipe down the
metal, then start over. If the mixture looks like a dark red stew,
definitely time to change it. You will also need to top off the
mixture with additional water if the level falls, as the process
cooks off water (electrically rips it apart).
FAR MORE INFO ON ELECTROLSIS RUST REMOVAL HERE:
Electrolytic Derusting, at StoveBolt.com
Electrolytic Rust Removal FAQ, by Ted Kinsey
Rust Removal using Electrolysis, at Antique-Engines.com
Note 1: CAUTION: DO NOT PLACE ANY FLAMES CLOSE TO THE MIXTURE, BECAUSE IT GENERATES FLAMABLE GASES.
Note 2: Reversing the polarity will give you undesirable results!
CYBERPOET'S RECOMMENDATION: POR-15.
SPECIAL NOTES, ANY PROCESS:
If your gas tank has rust that has moved all the way through the
base metal, as evidenced by paint bubbling on the exterior of the
tank or as leaks through the tank, do not use any of these methods,
but instead replace the tank with a known-good one (new or used).
None of the methods above will add any significant structural
integrity to your tank, and you don't want to be riding with a tank
that is ready to split like an over-ripe watermelon the first time
it hits the ground (or might even breach on a simple hard jostle to
the suspension, such as a pot hole), because it could easily
translate into meaning that you are turned into a fireball (and
subsequent death or spending an awfully long and painful visit in a
burn trauma ward).
If you have a rusted-through gas
tank (or on the verge of rusted-through) to a bike that is so old and/or rare that no other tanks can be
found, send it to a specialized shop that will either replicate it from scratch, or will cut it open, cut/grind away
the compromised portions and reweld fresh metal into the voids, and then grind it smooth
again, so you have structural integrity. Do not compromise your own safety in this sense! In the USA, we suggest
contacting Bob Brown at EmpireGP for this kind of work.