I have a Caswell-lined fibreglass tank and wondering if I should, or need to, remove fuel mix while storing over the winter (Canadian) and if so, should I replace it with something or okay to leave empty. For my street bikes I just top up tank and add a bit of stabilizer. I asked my neighbour who owns a boat and he says it should be fine if it's treated/lined as it protects from ethanol. Thanks in advance.

Edited December 3, 2025Dec 3 by Blanco

I would not leave fuel with ethanol in any motorcycle over the winter regardless of the tank material. Stabilizers may be helpful in preserving fuel but I would not count on them. Even though your tank is coated I think it is still a bit risky to ever use ethanol containing fuel in a fiberglass tank.

While it's probably OK to leave fuel in it, it would be kinder to the tank liner to store the tank dry over winter. Nowadays after a ride, I drain and dry out my lined fibreglass tanks if it will be more than a few weeks until the next ride. My oldest epoxy tank liner is about 20 years old now. For the first 15 years I left that one with fuel in between rides and it gradually changed from honey colour to dark brown over the 15 years. After I noticed this happening I started draining it between rides and now at 20 years it is still working fine. It may still have been OK if I had continued leaving fuel in it, but the colour change made me wonder if it was being gradually damaged structurally. 

For info, Caswell liner is epoxy resin

Thanks for the advice. I will drain for storage. And draining between trials events probably is a good habit in season. I'd consider replacing with aluminium tank if not so pricey! Cheers.

I don't know for sure but I have heard the welding on the seams of the aluminum tanks is poor.