Fuel Leak Repair for Toro Proline 21" Recycler II Mower

You smell the strong odor of fuel. Look for the telltale signs of a leak

In this photo there are dark stains on the hull of the rotary mower directly beneath the fuel tank. Grass clippings are stuck there. The dark stains are caused by the 2-stroke oil in the gas.

A closer look shows that the fuel line looks damp starting at the base of the tank. Grass clippings are stuck to the fuel line. The leak is here.

Wiping off the fuel line shows that a while plastic elbow exits the bottom of the plastic fuel tank. Hose clamps attach the black plastic fuel line to the elbow and to the fuel filter.

Look carefully to see what might be causing the fuel leak. The plastic tank could be cracked, if something heavy fell on it.

If the tank looks okay from the outside, empty the tank and look inside through the fuel filler cap.

In my case the leak started after decades of light usage. Removing the white elbow showed that the O-ring was flattened. This is my prime suspect for the cause of the fuel leak.

Fuel is getting past the flattened O-ring, passing through the threads, and running down the outside of the fuel line. The easiest repair is to replace the O-ring. I happened to have some O-rings that are the right size, but don't know if these are made from special ethanol-resistant material.

One possibility is to use regular plumber's pipe dope to seal the threads. My tube says it is good for pipes carrying a variety of substances, but doesn't say what those are.

Another possibility is to use plumber's teflon tape on the threads. Gasoline attacks regular white teflon tape, which will could eventually cause a piece to break off and cause engine trouble. Yellow teflon tape may be rated for use with gasoline, but only on metal threads. It isn't recommended for plastic parts.

A third possibility is to apply some kind of thread locker like blue Loctite to the threads of the white plastic elbow and the black plastic fuel tank, but blue Loctite is specifically not recommended for plastic threads.

As far as I can tell, the only non-hardening thread sealant that is resistant to gasoline AND also rated for plastic threads is Permatex 80019 Aviation Form-A-Gasket No. 3 Sealant. This wasn't available at my local hardware store, but it came in two days via mail order.

There is a brush attached to the container lid. Brush a thin coat onto both sets of threads, wait several minutes, and then screw the parts together.

Caution: Permatex Aviation comes with all sorts of warnings. It causes cancer. Do not touch it, ingest it, or inhale fumes. Wear disposable plastic gloves, protective eyewear, and a mask when using it.

Wait. According to the online instructions, Permatex Aviation fully cures in 24 hours, forming a gasket. The bond is not permanent, which is good if like me you anticipate needing to remove the elbow again in the future.

While you are waiting for the Permatex to cure, do some maintenance. Gently clean the air filter sponge with soapy water (do not wring: instead, press between towels) and re-oil it. Using a grease gun, shoot two pumps of grease into each of the three zirt fittings: the gearbox and behind each of the two rear axles.

You're done! Fill your tank up with the gas/2-stroke oil mixture, and resume cutting your lawn. Check the fuel line for leakage over the next few days, to make sure you fixed the problem.