Transmission Oil Cooler Flush: What Happens When It Fails & What Can You Do?

transmission oil coolers
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Whether you’re always off touring or camping, or just like the odd weekend in the outback, knowing how to flush out your transmission oil cooler is essential for keeping your 4×4 in top condition and ready for action. However, when it comes to flushing out this important system, things can go wrong. So, what can you do? The answer to that and more are in this blog.

3 Reasons to Flush Your Transmission Oil Cooler This Weekend

Transmission oil coolers are an important component of your car’s automatic transmission system. They help to cool the transmission fluid, which in turn helps to prevent overheating and extend the lifespan of your car’s transmission. Over time, however, they can become clogged with debris. This reduces their effectiveness and can even cause damage to the transmission if left alone. 

When you flush your transmission oil cooler what you’re doing is:

  1. Removing debris: Debris such as dirt, metal particles and sludge can clog the cooler. Flushing it helps get rid of these nasties before they can do damage. 
  2. Restoring efficiency: A clogged transmission oil cooler will not cool the transmission fluid as effectively. For optimal performance, you want your transmission oil cooler to be clog free.
  3. Preventing transmission failure: If your car’s transmission fluid is not cooled properly, the chance of the transmission overheating or breaking increases as it is less lubricated and protected. This can lead to premature wear and tear and, ultimately, transmission failure.

If that isn’t enough to make you want to flush your transmission oil cooler, there’s some other things to consider too. If you don’t flush your cooler, then you’re:

  1. Reducing your transmission’s lifespan: When your transmission is damaged or becomes overheated, it is likely to last for a shorter period of time.
  2. Reducing your transmission’s performance: A transmission that is not properly cooled can experience a range of problems, including slipping, rough shifting, and other performance issues. This can be a serious problem when off-roading or on the highway.
  3. Setting yourself up for costly repairs: If your transmission gets damaged due to clogs, you might need to pay for expensive repairs or even a complete replacement.

Can’t I Just Replace the Oil Rather Than Doing a Full Transmission Cooler Flush?

While it can be tempting to just replace the transmission oil and declare the job done, it’s not as simple as that. Flushing the transmission oil cooler and replacing the oil are both important maintenance tasks that serve different purposes.

Replacing the oil helps keep the transmission properly lubricated, preventing wear and tear on the transmission components. On the other hand, flushing the transmission oil cooler aims to remove debris and contaminants from the system. This ensures that the transmission oil will be properly cooled to avoid overheating and damaging the transmission.

For many auto-experts and enthusiasts, flushing the oil cooler is seen as the more important of the tasks — but both should be done regularly.

What Can Go Wrong If You Incorrectly Flush Your Transmission Cooler Lines?

With that being said, however, when it comes to your transmission oil cooler flush, you want to be sure you’re doing it right. Otherwise, you’ll find yourself dealing with problems like:

  • Over-pressurization: If too much pressure is used during the flushing process, it can damage the transmission oil cooler or even rupture it, causing leaks or other problems.
  • Contamination: If the flushing equipment or fluids are not properly cleaned or contain contaminants, they can introduce new debris or contaminants into the transmission oil cooler, which can cause additional damage or clogging.
  • Insufficient flushing: If the flushing process is not thorough enough, it may not completely remove all the debris or contaminants from the transmission oil cooler. While you’ll likely see some improvement to your transmission cooling, the job isn’t finished yet.
  • Incorrect fluid use: If the wrong type of fluid is used during the flushing process, it can cause damage to the transmission or the cooler.
  • Improper reinstallation: If the transmission oil cooler is not reinstalled correctly, it can leak, work ineffectively or cause damage to the transmission. You want to be sure all transmission oil cooler fittings are properly replaced.

Issues like these are plenty of justification to make sure to get your trusted mechanic to flush your oil cooler or to be very thorough and cautious if you’re doing it yourself.

Help! I’m Not Sure If I Made a Mistake Flushing My Transmission Cooler.

As with most things automotive, you can look for certain signs to tell you if your flush was successful or not. If you notice any of the below, your flush likely wasn’t successful or was not properly conducted.

  • There’s leaks: If there are leaks around the transmission oil cooler, it may be a sign that it was damaged during the flushing process.
  • Your transmission is overheating: Flushing your cooler is meant to prevent overheating. So, if your transmission is overheating, it usually means the transmission oil cooler was not properly cleaned or reinstalled.
  • Your transmission is shifting poorly: If the transmission is shifting more roughly than before, it could indicate that the fluid was not properly flushed and there is debris remaining in the transmission oil cooler.
  • Your transmission is slipping: As with the above, a slipping or erratically shifting transmission is slipping or shifting erratically can mean something didn’t go right.
  • The fluid looks contaminated: If the fluid coming out of the transmission looks dirty or contains debris, the flush may not have worked as intended.

I Didn’t Flush My Transmission Oil Cooler Properly — What Can I Do?

Relax, it is usually possible to repair the damage to your oil cooler from your failed flush. For instance, you may just need to weld or patch a crack, hole or puncture. Alternatively, you may be able to replace a damaged section. 

Of course, while you can repair your oil cooler, it may not be the most cost-effective option. Similarly, depending on what went wrong, there may be issues to resolve with your transmission too. As a result, fixing your oil cooler only may not be the right solution.

Flushing Your Transmission Cooler the Right Way

If you aren’t a car expert, it’s best to visit your mechanic to get your transmission cooler flushed. However, if you’re curious to know what they’ll do, below are the general steps for flushing out the cooler.

  1. Safely and securely raise the vehicle: This ensures that you can reach the transmission and transmission oil cooler.
  2. Drain the old fluid: Locate the transmission fluid drain plug and drain the old fluid into a suitable container. If you are flushing the transmission for the first time, you may need to drain the fluid multiple times to remove as much of the old fluid as possible.
  3. Disconnect the oil lines: Locate the oil lines that connect the transmission oil cooler to the transmission and disconnect them. Be prepared for some oil spillage.
  4. Flush the cooler: Connect a flushing machine or a garden hose to the cooler inlet and flush the cooler until the fluid runs clear. You may need to flush in both directions to remove as much debris as possible.
  5. Reconnect the oil lines: Once the cooler is flushed, reconnect the oil lines to the transmission and tighten them securely.
  6. Refill the transmission: Fill the transmission with fresh fluid according to the manufacturer’s recommendations.
  7. Check for leaks: Once the fluid is filled, start your car and check for leaks around the transmission and the cooler.

Ready to Be on Top of Your Transmission Oil?

If things have gone completely off the rails, or it’s just time for a new transmission oil cooler, you can always trust the team at KAON. Passionate 4WDers themselves, they’ve created a range of quality transmission oil coolers for a range of Australia’s most popular touring 4x4s. Designed with real-world experience and quality materials, these coolers will have you back on any road, whether it’s beaten or not. So, explore their range today, and don’t forget to flush that new oil cooler.

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Mike Trans

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