How to Repair a Cracked Coolant Reservoir

"Engine coolant only" printed on the side of a plastic coolant reservoir.
  • 3-6 hours
  • Advanced
  • 20-200
What You'll Need
Siphon hose
Drain bucket
Screwdriver set
Ratchet and socket set
Water hose
Plastic weld or epoxy
Radiator pressure tester

A crack in your car's coolant reservoir can mean bad news for the safe and efficient operation of your engine. As your engine heats up during operation, the coolant reservoir serves as a temporary container for your car's coolant as it is expelled from your radiator. Then, when the temperature of your engine cools, the stored coolant is replenished into the radiator itself. Although it is relatively easy to diagnose and even fix a crack in your radiator reservoir, extreme caution must be taken due to the intense pressure that this component is under during operation. It is almost always a better idea to replace a cracked reservoir entirely, but below you will find steps that you can use for a quick solution.

Step 1 - Remove Coolant

Using your siphon hose and bucket, the first thing you will need to do is siphon all coolant out of the reservoir itself.

Step 2 - Find Leak

Carefully examine the reservoir entirely. Once the leak is identified, you will want to mark it clearly with a marker so that you do not lose track of it in later steps.

Step 3 - Release Pressure

Since the radiator, and especially the coolant reservoir, will be under pressure when the engine is in use or has recently been turned off, be sure to complete this step when you are sure that the engine has cooled completely. Relieve any pressure in the radiator system by releasing the cap on either the radiator or the coolant reservoir itself.

Step 4 - Remove Overflow Tube

Looking at the radiator and coolant reservoir, you will see a tube connecting the two components, known as the overflow tube. You will need to disconnect this in order to continue. Often, there will be a ring clamp present that can be adjusted with pliers. Once the tube is clamped off, remove it where it connects to the coolant reservoir.

Step 5 - Remove Coolant Reservoir

A series of bolts and/or screws will typically attach your coolant reservoir to the chassis of your vehicle. You will need to carefully remove these one by one, making sure to keep track of them as they're removed since you will need them to reattach the coolant reservoir when you are finished. After removing the coolant reservoir, shake it upside down to remove any remaining coolant that is still left after siphoning.

Step 6 - Clean Reservoir

Wash the reservoir thoroughly, both inside and out with your water hose. Then, allow the reservoir to dry completely before continuing. Sand the area to be repaired for better epoxy adhesion.

Step 7 - Apply Epoxy

Prepare plastic welding product or epoxy according to the manufacturer's instructions, and then carefully apply it to the coolant reservoir as directed. Thoroughly work the plastic weld or epoxy into the crack to ensure a complete seal. Allow the product to cure for the recommended amount of time before continuing.

Step 8 - Replace Components and Test

Once the epoxy has been given time to dry, reattach the coolant reservoir by using your same method from earlier in reverse. Then, refill the reservoir with coolant and test the system with a radiator pressure tester to make sure your repair has succeeded and that the reservoir it is working properly.