Catalytic Converter Rattles: What Causes & How to Fix the Issue

The catalytic converter is an essential component of any car, and just like any other vital part, it can sometimes become a cause for concern. Car owners sometimes hear rattling and other noises from their catalytic converters, which are bound to ring alarm bells on their heads. Fortunately, the issue is easily fixable most of the time.

A catalytic converter may rattle because the heat shield has become loose or the honeycomb has started deteriorating. You can solve the problem by tightening the heat shield and cleaning the cat. You may have to replace it. It’s usually not dangerous to drive with a rattling catalytic converter.

Let’s look at some of the most common causes of catalytic converter rattle and what you can do to fix and prevent the issue.

Why Does My Catalytic Converter Rattle?

Your catalytic converter rattles because the heat shield has become loose and starts clanging against the cab floor. Alternatively, the honeycomb structure inside can become blocked or damaged, causing the noise you’re hearing.

Let’s briefly examine these two problems.

Loose Heat Shield

Every catalytic converter has a heat shield to prevent the extreme temperatures generated in the converter from damaging your car’s floor. Without it, the head could be enough to melt through it or cause damage in some other way.

The heat shield is usually screwed on, and the screws may become loose over time, they can be eaten away by corrosion or even fall off. This will cause the heat shield to move around as you’re driving, hitting the floor of your car. If the rattling is louder while accelerating, it strongly indicates that there’s something loose in your exhaust system.

A loose heat shield is not particularly dangerous in and of itself. However, driving around with it may cause it to become loose and eventually fall off, so you should take action and fix it as soon as possible to prevent the problem from worsening.

Cracked Honeycomb Structure

The ceramic honeycomb structure inside the catalytic converter is prone to damage over time. You may have accidentally smashed it against something and cracked it while driving, without even remembering, causing the cracked pieces to rattle.

Alternatively, the high temperatures in the converter may cause the honeycomb structure to crack, which you may hear when the different pieces move around the converter. In some cases, the heat may even fuse some parts of the honeycomb, or they can be blocked by build-up.

If there’s a problem with this structure, you might be in trouble, as issues with a honeycomb are far more dangerous than those you might experience with a heat shield. Issues with the structure can lead to engine problems and serious damage to your car, so they need to be fixed with even more urgency than the heat shield.

Let’s look at what other noises you can hear from a bad converter.

Other Noises From the Converter

A bad catalytic converter can produce other noises apart from rattle. It’s important to know what these noises mean, so you can be proactive regarding your cat’s maintenance.

These noises include:

  • Ticking: You can hear this noise when the converter is burning off oil, fuel, or coolant. It can also be caused by a leak somewhere in the converter. It’s often heard during a cold start, acceleration, or idling.
  • Pinging: A pinging sound from your converter usually indicates clogging because of age, overuse, or fuel contamination.
  • Knocking: This is also often caused by a loose shield or a leak.
  • Popping: This noise usually occurs because there is a clog in the converter and it’s restricting exhaust flow and causing backpressure.

Now that we’ve established what noises a catalytic converter may make, let’s take a look at other signs that there’s something wrong.

Other Signs of a Bad Catalytic Converter

Apart from rattling and making other noises, a bad catalytic converter may send you a few different signals telling you that something is wrong.

These signs include:

  • A failed emissions test: Since a catalytic converter reduces pollutants in your exhaust, failing an emissions test (if it exists in your district) is a clear sign that there is something wrong with it and that you have to fix it. Furthermore, if the exhaust has suddenly become darker, it’s another tell-tale sign that your converter is not working properly.
  • Poor engine performance: If your converter is leaking or is clogged, the engine won’t be able to expel the exhaust properly, leading to problems with its performance. You might notice that acceleration is slower, stutters, or that it’s increasingly difficult to go uphill. Sometimes, there may even be a complete loss of power.
  • Rotten egg smell: Hydrogen-sulfide is a byproduct of gas that contains sulfur. It has a distinct rotten egg smell (like anything with sulfur). A properly working converter converts hydrogen-sulfide into sulfur dioxide, which is odorless and unnoticeable. If your exhaust has a rotten egg smell, that means that your cat is not working as it should.
  • Lower gas mileage: A bad cat can make your car spend more gas per mile because of problems with the engine and combustion. The engine will struggle to expel exhaust gasses or it may experience problems with starting, which reduces fuel efficiency. If you’re suddenly guzzling more gas than before, it might be because of your converter.
  • Check engine warning: Since a bad catalytic converter may cause engine problems, the “check engine” light will probably turn on. If it seems like there’s nothing wrong, you might have a problem with your converter. Alternatively, the sensor may be dirty, but that option is not very likely.
  • Engine misfires: A clogged converter may cause back pressure and a lack of oxygen necessary for combustion in the engine, causing the engine to misfire. If your engine has been misfiring often recently, it might be due to a problem with the cat.

How to Fix a Rattling Catalytic Converter

To fix a rattling catalytic converter, you can try cleaning it, tightening the heat shield, using better fuel, or replacing the converter altogether. If all fails, don’t hesitate to consult with a professional.

Getting rid of the noise from your catalytic converter usually doesn’t require a big investment, and you can do most of the fixes on your own. The only exception is replacing your cat since they tend to get quite costly, and it’s best not to do it alone.

Let’s take a deeper look at these fixes and see what you can do.

Cleaning Your Catalytic Converter

Over time, you might get a lot of build-up in your catalytic converter, which can cause poor performance and other issues. That’s why it’s best to resort to cleaning if you hear any noise.

You can choose from a few different products for cleaning your converter. There are cleaning products made specifically for this job, but you can also get away with using other items. The products you can use include:

  • Lacquer thinner: While this is not made specifically for cleaning your converter, it makes for a simple and inexpensive way to clean it, with great results. When your tank gets empty or almost empty, pour in a gallon of lacquer thinner, and then 10 gallons of gasoline. Go for a two-hour ride and make sure your engine is working at 2,500 rpm. After 50 to 70 miles, you should experience improved performance and the rattle should stop too.
  • Sodium hydroxide: This is a good fix for situations in which your exhaust smells like rotten eggs. Sodium hydroxide will remove the hydrogen sulfide that causes the smell. You should pour sodium hydroxide into a spray bottle and then spray generous amounts of it into the honeycomb from both sides. Let it sit for 20 to 30 minutes, and wash thoroughly. Reinstall the converter, and you’ll be good to go.
  • Sea Foam SS14: This is a dedicated cleaner for removing carbon and other types of residue from various parts of the car. You should warm up your engine before using it, and then attach the bottle to the spray canister and empty it into it. Run the engine for 10 minutes, let it rest, and then run it again for 10 minutes, revving periodically.
  • Cataclean: This is another great tool for cleaning all sorts of buildup in your engine and cat. When your tank gets down to four gallons, pour in a 16 oz bottle of cataclean and go for a 15-minute ride to get into the engine and converter. You should notice an improvement in the performance.

Tighten the Heat Shield

If a loose heat shield produces the rattle, then the only thing you can do is tighten it. Otherwise, it might fall off or trap small rocks between it and the catalytic converter, causing even more rattle. Thankfully, this is a pretty easy fix.

  1. Remove all corroded bolts. Use penetrating oil if necessary.
  2. Clean the heat shield and the converter’s body. Use sandpaper if necessary.
  3. Put the shield back in its place and use new bolts to bolt it into place.
  4. Tighten everything so it doesn’t get loose again.

If the heat shield is damaged, you might have to get a new one, so be ready for that expense. Hopefully, it won’t come to that, and you’ll get rid of the rattle in a few simple steps.

Use Better Fuel

This is the simplest fix that you can resort to. Low-quality, low-octane fuel tends to produce more build-up in the engine and cat, whereas high-quality, high-octane fuel creates less build-up and thus causes fewer problems.

Of course, this fuel is more expensive, but it can save you some money in the long run. It’s cheaper than a new catalytic converter, and it can also give you better mileage and reduce other problems that you might have.

Overall, switching to better fuel is a good idea even if you don’t have problems with your catalytic converter, and it may prevent you from having to deal with them in the first place.

Replace the Converter

Sometimes, the converter can be so damaged that there is no way to restore it to its former glory. In that case, the only course of action is replacing it, even though it can be costly. You might save some money if you buy an aftermarket converter and do it on your own, but the best thing is to get an OEM converter and pay a professional to do it.

On the other hand, if you’ve got some mechanical experience, you can do it on your own, especially if you’re confident in your skills. There aren’t many steps, but you have to be careful, so you don’t spend even more money:

  1. Cover the bolts in penetrating oil.
  2. Let the oil sit, then carefully unscrew the bolts.
  3. Set the converter in place, along with the bolts.
  4. Screw the bolts in, adding an anti-seize compound to each of them.

After that, you can go on a test ride and see if there’s any improvement in your car’s performance.

Is It Safe to Drive With a Rattling Catalytic Converter?

It’s mostly safe to drive with a rattling catalytic converter, but it’s not good for the environment, and it may cause further damage to the converter. If your converter is broken and causes back pressure, you should not drive, as doing so can cause engine problems.

If your heat shield is loose, causing rattling, then it’s technically safe to drive. However, the more you drive with a loose heat shield, the more it’s likely to fall off, and the cat is more likely to get damaged. Therefore, it’s best to get it fixed as soon as possible.

If there is something wrong with the honeycomb structure in the converter, it’s still mostly safe, but it’s bad for the environment, and you might also fail an emissions test. So, you should never waste time when it comes to fixing your cat.

On the other hand, if the converter is blocked, it’s not particularly safe to drive. It can make your engine perform poorly and cause misfires, starting problems, and stalls. This might damage your engine and cause further problems and expenses, so you should not drive if your catalytic converter is blocked.

Final Thoughts

A catalytic converter usually rattles because the heat shield has become too loose or something else is broken inside. You should invest in the maintenance of your catalytic converter and get it fixed as soon as you notice issues because even the most benign problems can progress to life-threatening dangers over time.

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