Keep the tank empty and the saw out of the weather.

The best way to keep the plastic fuel tank from turning brittle is to drain it and keep the saw out of the cold as much as possible. If you have to leave a chainsaw outside all winter, an empty tank is your cheapest insurance.

Cold makes plastic stiff, but the real damage comes from ethanol fuel and sunlight. Ethanol pulls in moisture, which can freeze and expand inside the tank, and UV slowly attacks the plastic itself. An empty tank means there’s nothing in there to freeze, expand, or stress the material.

So before storage: drain the tank, run the engine until it stalls to clear the carburetor, and wipe the outside dry. Then keep the saw off the ground, covered with a tarp or in a plastic bin, away from direct sun. A shed is better than a fence. A garage is better than a shed. The less weather it sees, the longer the tank survives.

If you absolutely can’t get it indoors, an empty tank and a cover are still going to beat a full tank in a snowdrift. That brittle plastic isn’t going to heal itself.