How to Fix Coolant Reservoir Tank Leaks

Coolant reservoir tank in a car.
  • 2-4 hours
  • Intermediate
  • 50-150
What You'll Need
Siphon hose
Water hose/water source
Radiator pressure tester
Ratchet socket set with extension

The coolant system in your car is a pressurized system. As you operate your car, the coolant in your radiator warms and expands, thus flowing into the reservoir tank. When your car cools, the excess coolant will cool as well and return back to the radiator, typically leaving the reservoir tank 1/3 full. A crack in the coolant reservoir could cause a slow leak of coolant and could also cause your car to overheat. You can easily diagnose and fix a coolant reservoir tank leak. This repair should always be made on a car that has cooled. Never open a radiator cap when the engine is hot.

Step 1 – Remove Fluid from Coolant Reservoir

Before you begin, make sure your car has been turned off for a while and has cooled. You do not want to work on your car and start to fix the coolant reservoir if your car is still warm.

Remove all of the coolant from the reservoir. In order to remove the coolant properly, use a siphon hose directed into a bucket and remove as much as possible. Remember to make sure your work area is clean and protected.

Step 2 – Note Leak Area

Examine the tank and determine where the leak is located. You should take a marker and circle this area.

Step 3 – Remove Radiator Cap

Remove the radiator cap from the cooled engine.

Step 4 – Disconnect Overflow Tube

Use a pair of pliers to move the clamp along the tube, and then twist the tube to remove it from the reservoir.

Step 5 – Disconnect Any Other Fittings and Remove Tank

You may find that your car has some additional fittings holding the tank. You will need to remove any of these before you proceed. You may even have to remove additional items to gain access to the tank and remove it.

Step 6 – Empty the Tank

You can now remove the remaining coolant from the reservoir into the bucket.

Step 7 – Wash the Tank

Use the water hose to wash the tank thoroughly inside and out. You will need to let the tank dry completely.

Step 8 – Apply Epoxy

Lightly scuff the cracked area with sandpaper for better epoxy adhesion. Blow sanding particles off area to be patched.

Mix the epoxy and allow it to set up according to the manufacturer’s instructions. When the epoxy is ready to apply, use an applicator and apply to the leak, pressing it into the crack as needed. Be sure the crack is completely filled. Allow epoxy to cure according to manufacturer’s instructions.

Step 9 – Replace Tank

Once the epoxy is dry it is time to replace the tank. Be sure to replace all fittings that you took out when you removed the tank.

Step 10 – Replace Coolant

Using a funnel, pour the coolant from the collection bucket back into the reservoir. Add new coolant to fill the tank to the fill line.

Step 11 – Retest the System

Retest the system using a radiator pressure tester.