How to Fix a Leaking Radiator Drain Petcock

January 27, 2012

The radiator drain petcock is the valve that helps you drain the coolant when you need to change it or work on it. However, this drain valve can begin to have leaking problems over the life of your car. Fixing a leaking radiator drain petcock is a simple process that requires some basic tools and time.

Tools and Materials

  • A new frain petcock
  • A socket wrench
  • Coolant
  • A screwdriver
  • A plastic container

Drain the Radiator
Place the plastic container underneath the radiator drain valve. Loosen the drain valve and let the coolant run into the container. Remove the radiator cap to allow the air to push the coolant out quicker.

Remove the Radiator Shroud
To save some time while the radiator is draining, you can remove the radiator shroud. Depending on the type of vehicle you are working on, there can be up to eight screws holding this in. Remove the screws and lift out the shroud.

Remove the Radiator
Unhook the upper and lower radiator hoses. They are connected with simple hose clamps. Loosen the pressure screws in order to loosen the clamps. Unbolt the radiator by the mounting bolts that are located on either side. Once all the bolts are removed from the radiator, carefully lift it out of the vehicle and set it on a work bench. Make sure to cover the bench with a cloth or tarp. You don't want to leave any type of coolant on the surface.

Remove the Retaining Clip
Since you already have the radiator drain petcock out of the radiator from draining it, you now have to remove the retaining clip. This is usually the part that fails and causes the drain valve to start leaking. Use an ice pick or something pointed to get in under the plastic and pop out the retaining clip. Clean the area of any debris with a clean rag.

Install the New Retainer
Unscrew the retaining clip from the new drain plug and place into the radiator. Place a small amount of sealant around the lips of the clip and push it into the drain hole. This simply pops into place. Make sure it pops in securely and flat.

Install the New Radiator Drain Petcock
Screw in the petcock. Rub a little Vaseline around the rubber gasket of the drain valve before you screw it into the retainer. As you screw the valve in, be careful not to overtighten. If it goes too tight, you will have problems with leaking again after the engine heats up a few times.

Replace the Radiator
Place the radiator back into the vehicle by reversing the removal instructions. Run water through the radiator to flush it out of any dirt or contaminants.

Check for Leaks
After you've run the engine a few times, continually check for leaks of the drain valve. If you see some drips, you need to tighten the radiator drain petcock a little. If there are large puddles, you will need to replace the valve again, as it is damaged from overtightening.

Related Questions and Answers

How do You find Your Radiator Petcock?

A radiator petcock must be located in the bottom of the radiator core in order to perform correctly. It is true that today's cars have cooling system overflow tanks, but they cannot be used to drain a system. To find a petcock, first check the car's owner's manual where schematic diagrams with callouts of various key parts are mapped. You will likely find the petcock marked on the engine schematic. If you cannot, then you will have to get under your car with a flashlight and find the winged butterfly nut that serves as the petcock. It will likely be in the front or rear face of the radiator.

Why is it Important for a Radiator Hose to be Flexible?

It is important that a radiator hose be flexible for several reasons. The first is the temperature ranges it must withstand. In the summer, one can find underhood temperatures to be almost 300F, a heat level that can easily deform a radiator hose. While in the winter, underhood temperatures can be a 0F or below where standard rubber can become brittle and break. A flexible radiator hose can withstand this wide range of temperature and the pressure within the system. A secondary reason flexibility is needed is because radiator hoses must be fit into some very interesting engine areas where fixed hoses would fail, because they cannot bend adequately.

Aluminum or Copper Radiator: What's Better for Cold Weather?

In general, a copper radiator is better for cold weather. Copper is a far better conductor of heat than aluminum. Aluminum radiators tend to be used as oil system intercoolers or turbocharger intercoolers where a more gradual heat exchange is perfectly acceptable. Copper systems tend to be more flexible and extract a higher amount of heat for a given area than aluminum systems. Also, aluminum systems can become brittle when exposed to the chemicals used in standard copper core radiator systems. Interestingly, because a copper radiator can have its heat exchange area expanded by using thinner walls and more vents, it is far more valuable as a radiator than aluminum.

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