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How to detect and repair a radiator or coolant leak

Your engine's radiator performs the essential task of cooling the radiator fluid (or coolant) that keeps your engine running at the proper temperature, and in many cases it also cools the automatic transmission fluid. There are no moving parts in a radiator, but corrosion from both inside and outside eventually takes its toll, resulting in a leak. A green puddle of coolant under your car is usually the first sign of a radiator leak. In most cases, this leak is small enough that you can add coolant until a replacement radiator can be obtained.

Modern radiators typically have aluminum cores (the finned part) and plastic side tanks. When used with today's modern radiator fluids (and with proper preventative maintenance), these modern radiators can last up to 150,000 miles. This was not always the case. The copper core and brass side tank radiator of most older vehicles typically lasts half that long. However, when you consider that newer vehicles have much more complex engine compartments with tight access to radiators, at least it is much easier to replace a radiator on an older vehicle.  

Note that the vehicle shown in these photos is an older vehicle without the usual "nest" of hoses and wires, and without a fan shroud. Newer vehicles will present a much more complicated job that can take much longer.

Setup
Park your vehicle in a well-lighted area – outside in daylight is best – and let your engine cool down before performing the next steps.

The first thing you need to do is locate the source of the coolant leak. It might not be coming from the radiator. The best way to confirm the source of the leak is to wash the radiator and hoses with water, and then start the engine and look for new signs of coolant.

If you have determined that the radiator is the culprit, there are a number of connections to the radiator that you will need to identify – and ensure that you can access – before attempting to remove the radiator. Check for each of the following:

  1. Look to see if the radiator has a shroud (duct work) that directs the flow of air through the radiator. This shroud will have to be removed in order to get to the radiator.
  2. Find the upper and lower radiator hose connections. You will need to remove these hoses at the point that they attach to the radiator. Can you reach them and their hose clamps?
  3. Is the vehicle equipped with electric cooling fans? These fans typically attach to the radiator frame. They may need to be removed before removing the radiator.
  4. Is your vehicle equipped with an automatic transmission? If so, there may be cooling lines that attach to the radiator side tank.
  5. How is the radiator attached to the vehicle? There are many different mounting methods. The most common are bolts through brackets on the radiator. However, some designs have rubber pads or pins that have separate clamping pieces bolted to the vehicle.

Point of no return #1
If you cannot locate or remove these items, or if you do not have the tools to perform this service, take your vehicle to a reputable shop and have a professional technician handle the job.


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Tools required

  • Screwdrivers
  • Socket wrenches and/or combination wrenches
  • Flare-nut wrenches (for automatic transmission lines)
  • A drain pan

Materials

  • Replacement radiator (new or "rebuilt")
  • New antifreeze and fresh water (distilled is best)
  • Silicone sealant
  • Paper towels

Many auto parts stores and dealerships offer replacement radiators for most newer vehicles. You will need to provide information about the exact model, engine size, transmission and accessories (such as air conditioning) on your vehicle in order to get the correct replacement radiator.

However, if you own an older vehicle, you may need to consider having your radiator rebuilt. This is called "re-coring," and it is a process where the finned part of the radiator is replaced while keeping your existing side tanks, hose locations and mounting brackets. If you opt for re-coring, count on some vehicle downtime between when you remove the old radiator and when you install the rebuilt one.

The job

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  • Step 1: Park your vehicle on a level surface in a well-lighted area. Let the engine cool down completely.
  • Step 2: If your vehicle is equipped with electric cooling fans, disconnect the battery.
  • Step 3: Drain the coolant from the radiator. (See "The importance of coolant" for detailed information.)

  • Step 4: Unclamp and remove the upper and lower radiator hoses from the radiator.
  • Step 5: Remove the fan shroud. The shroud may be attached to the radiator or to the radiator-supporting frame. It is usually either clipped in place or is held by screws or bolts. You may have to wiggle the shroud back and forth around the fan blades and brackets to completely remove it. Some shrouds are multi-piece arrangements, so make sure you remember how the pieces fit together. Removing the fan shroud sometimes even requires the removal of the engine cooling fan. The fan is usually bolted to the water pump with four small bolts.
  • Point of no return #2
    If you cannot remove the fan shroud, stop and reassemble any pieces that you've removed and refill the radiator with a mix of antifreeze and water. Let a professional technician do the job for you.

  • Step 6: If your vehicle is equipped with an automatic transmission, check for metal lines running into the radiator side tank. There should be nuts at the end of these lines that disconnect the lines from the radiator side tank. You may need to use a specialty wrench, called a flare-nut wrench, to get a decent grip on these nuts without damaging the lines.
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  • Step 7: Now remove the radiator mounting bolts or clamps. These can usually be reached with a combination wrench or socket wrench. You may need an extension on the socket wrench to reach past the radiator side tanks.
  • Step 8: At this point you should be able to slide the radiator upward and out of the vehicle. Be careful, since there may still be some coolant in the radiator or the disconnected hoses.
  • Step 9: Be sure to save any rubber mounting pads that may be stuck to the radiator brackets. You will need these when you mount the replacement radiator.
  • Step 10: If you are using a replacement radiator, make sure that it is identical to the old one that you just removed. Compare the exact size as well as the placement and type of fittings, and the mounting brackets.
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  • Step 11: Install the replacement radiator using the rubber pads and mounting bolts and clamps that you removed. Tighten the bolts approximately as tight as they were when you loosened them.
  • Step 12: If equipped, reconnect the automatic transmission lines. Tighten them as tight as they were originally.
  • Step 13: If equipped, replace the electric cooling fans. Be sure to route the wires exactly as they were originally.
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  • Step 14: If equipped, replace the fan shroud. Try to recall exactly how you removed the shroud and reverse the process. Again, you may need to jockey the shroud around to get it in place again. If you had to remove the engine fan, replace it.
  • Step 15: Reconnect the upper and lower radiator hoses. Use a silicone sealant to help seal the hoses and prevent future leaks at these connections.
  • Step 16: Refill the radiator with a fresh mixture of antifreeze and water. Distilled water is recommended, since it has fewer impurities that could lead to corrosion.
  • Step 17: Check that everything is properly installed and tight. If you disconnected the battery, reconnect it now.
  • Step 18: Start the engine and visually check for leaks. Remember that you may need to look for both coolant and automatic transmission fluid leaks.
  • Step 19: Check to see that the fan blades are not rubbing against the fan shroud, indicating that the shroud is not properly located. If there is a problem, shut off the engine and reposition the fan shroud.
  • Step 20: If everything looks and sounds right, take a short drive around the block and keep an eye on the temperature gauge. Check for leaks when you return. During the next week, check your coolant level periodically to ensure that the entire system is sound.

  • Cleanup
    Clean and store your tools. Dispose of any used coolant properly. Remember: Antifreeze is both attractive and poisonous to many animals. Most local or county governments have recycling centers that will accept used coolant. Any antifreeze that may have dripped on the ground should be flushed thoroughly with a hose.

    Return your used radiator to the shop where you bought the replacement or re-core, or dispose of it properly. Now you're ready for both summer's heat and winter's cold.

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