Should You Seal Your Motorcycle Gas Tank

As I get closer to the end of my Shovelhead restoration project (aka “Cal“), I have been doing a little reading on whether or not I should seal my motorcycle gas tank.  This is a hot issue in motorcycle forums, and I figure if you are debating whether or not to seal your motorcycle gas tank, this might help.

I have never sealed a motorcycle gas tank in the past, but also have never (1) bought a brand new gas tank from an aftermarket supplier (2) had leaks in any of my prior projects’ gas tanks or (3) had a completely out of control interior gas tank rust situation.

These are the three situations I am aware of where sealing a motorcycle gas tank might make sense, so let’s discuss each separately (since in my opinion, the right answer for whether or not to seal your motorcycle gas tank is different based on the situation).

The bottom line when it comes to using a gas tank sealer is that it is VERY hard to do it yourself and truly do a good job.

Why is that?

Because after cleaning the inside of the tank, the next step to seal your motorcycle gas tank is generally to “evenly swish” the sealer around inside the tank.

The challenges here are that the liquid sealer dries very quickly, it is hard to know if it is even (unless you are Superman and can see through metal), and the outdoor temperature and humidity impact dry time and quality – could cause cracking.

Thinking in terms of risk and reward – the reward is potentially a “pretty well-coated” tank (big air quotes on that one); while the risks include:

– You miss spots or entire sections of the tank interior

– The final sealant coating is clumpy/cracked

– The sealant flakes off the inside of the gas tank over time

Broken off sealant can flow into your carburetor and engine and cause expensive damage.  A very serious risk!

All that said, I have heard of radiator shops doing absolutely perfect, professional jobs for between $40 and $60.  That is really not bad.  They have temperature controlled foolproof methods for getting the job done right (plus they are accepting liability for a job well done).  And, in that fact lies the perfect compromise for the scenarios described:

1) A Brand New Tank – a brand new tank of decent quality generally does not need to be sealed.  A metal’s susceptibility to rusting will depend on its composition.  Again, in general, a tank will not rust if kept full of gasoline and used regularly.  Therefore, my suggestion for a new tank is either don’t get it sealed or get it sealed by a professional.  Nothing would be worse than to try and coat an expensive new gas tank yourself and it to turn into a clumpy, flake ridden mess.

2) A Leaky Tank – To really repair a leaky gas tank requires welding of the leaks.  Sealant alone WILL NOT plug a leak, and it may make the subsequent welding job (that will be required) more difficult.  I have heard horror stories about people trying to remove sealant after applying it.  The stuff wasn’t designed to be removed, so you can imagine how horrible, frustrating, and time consuming that might be.  In general, a restorer adamant on repairing a leaky tank has a good reason for sticking it out with the existing tank – that is, the tank probably can’t be replaced – for example, it is an early Harley box tank for which few originals exist.  Therefore, my reasoning here is the same as above – weld and don’t seal unless you are willing to pay a pro to do it.  It is worth spending the few extra bucks to get it done right (tank seal kits cost almost as much as the radiator shop job described above).

3) A Very Rusty Tank – A rusty gas tank, even one in the worst of condition can be treated with a combination of vinegar and backing soda (both super cheap items) – see my related post on how to remove rust.  Once done, keep your freshly de-rusted tank full of gas.  As an additional precaution, use an in-tank (petcock attached) fuel filter AND/OR an in-line fuel filter between the gas tank and the carburetor.  Both of these cost about $10 or less and are much lower risk than trying to coat the interior of the tank yourself.  Sure if money is no object, you can have a pro do a seal job; but if you are like me and looking to do things both right and affordably, the fuel filter option will prevent any minor lingering rust from flowing where it shouldn’t.

Thanks for reading this long post about whether or not to seal your motorcycle gas tank.

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Didn’t find what you needed in this particular post?  Check out the HappyWrench Motorcycle Repair Link Database.  It is a one-stop shop for all your DIY motorcycle repair information needs.

Also, forgive any typos or grammatical errors a I wrote this blog post from my phone.

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