How to Repair a Leaking Filler Tube

a person working on a car
  • 1-8 hours
  • Beginner
  • 15-200
What You'll Need
Secure vehicle jacks or a hoist
Box socket wrenches, various sizes
Needle nose pliers
Trouble light
Replacement gaskets
Replacement O-rings
Replacement tube couplings
Replacement hose clamps
Replacement fluid for transmission or radiator
Replacement gas tank or radiator

In your vehicle a leaking filler tube can cause fluid loss from the radiator, the gas tank or the transmission. Any loss of these fluids can lead to reduced engine or transmission efficiency. Engine or transmission damage from coolant or transmission fluid loss can be severe, and result in costly repair and replacement. Follow the steps below to repair a leaking filler tube before major engine damage happens.

Step 1: Determine Where the Filler Tube Is Leaking

Figure out whether it is the coolant, the gasoline or the transmission fluid. Lift your vehicle securely off the ground with jacks or a hoist. Inspect the entire leaking filler tube with a bright light to determine where it is leaking.

Step 2: Drain Out Fluids

To repair a gas tank filler tube, drain out about 6 gallons of gasoline. Drain the entire transmission to repair a transmission filler tube. Drain about 2 liters of coolant to repair the coolant filler tube.

Step 3: Remove and Inspect the Filler Tube

With the correct sized box socket wrench, or needle nose pliers, remove the screws holding the filler tube to the applicable part. Set them in a container so they don't roll away. Inspect the filler tube couplings. Check for stripped screw holes, crimped metal or corrosion that could have started the leak. If the filler tube coupling is damaged, get a new filler tube and install it. Check for damage to the hose caused by the hose clamps. If the hose or clamps are damaged, replace them. Buy good quality rubber hoses and filler tubes for replacement instead of thin plastic tubing that can crack in either high or low temperatures. Examine the air vent on the filler tube to check for blockage. This may cause fluid to bubble back toward the radiator, transmission, or gas tank, starting a leak.

Step 4: Check Gaskets and O-Rings

After years of use, the gaskets and o-rings that help create a leakproof seal for filler tubes can stiffen and cause gaps in the seal. Check the gasket or o-ring at each end of the filler tube and replace if it is stiff, cracked or warped. If the new o-ring or gasket is dry, lubricate it with petroleum jelly or other approved lubricant before inserting into the filler tube coupling.

Step 5: Check at the Hose Connection for Corrosion

Examine the filler tube connection point to the transmission, gas tank or radiator. Check for corrosion, built-up dirt, or other problems. Clean the connection with a stiff wire brush to remove dirt and contaminants. If the filler tube connection to the gas tank or radiator is damaged, you may need to replace the tank or radiator.

Step 6: Reattach the Filler Tube

Reattach the filler tube at both ends and refill the fluid with new transmission fluid, coolant, or gasoline. Start the engine and check whether fluid is still leaking.

Step 7: If Fluid Still Leaks

Adjust the pressure in the applicable fluid pump, as it may be too high.