What Causes Rod Knock? (The One True Cause)

When your engine starts to make an unfamiliar noise, this can be very unnerving. You wonder what is wrong and how much it will cost to fix. Your engine is the primary reason why your car runs smoothly and provides you with safe transportation, so an engine problem (like rod knock) is the last one you want to encounter.

In this article, we’ll take a look at what rod knock is, what causes the issue, and how much it costs to fix it.

Rod Knock: Understanding the Problem

If your car is experiencing rod knock, it sounds like a persistent tapping from the inside that gets louder when you speed up. There are other problems that can make a similar sound, but you need to determine if you actually have rod knock or not to truly fix the issue.

The name is very literal because rod knock is the action of a loose rod knocking against the crank as it rotates. An engine is crafted with gap tolerances, which allows oil to enter and create a barrier between these surfaces. When the barrier wears down, the gaps become wider and the oil will no longer settle where it needs to stay.

Without this protective barrier, rod knock can develop over time. Normal wear and tear can be a cause, but this often takes hundreds of thousands of miles before it occurs. There is usually another cause as to why rod knock happens.

When your engine warms up and the sound goes away, this means it is likely not rod knock. You still have an issue to identify, but at least you can rule out one of them to help you understand what is actually going on.

The Main Cause of Rod Knock

Although there are many things that can happen to your car that mimics rod knock, there is only one true cause. Below you will learn about this cause and some others that might mislead you because they cause similar noises to happen.

Worn Bearings

This is the only cause of rod knock. When bearings wear down, they are also notorious for shifting positions in the process. After this happens, the piston rods in the engine will begin hitting the crankshaft. This is the knocking noise you are hearing from the inside.

Low Octane

If there is low octane in your engine, this will create a similar noise. It is known as a detonation knock, and it happens when the air and fuel mix in multiple places at a time. This noise is often interpreted as rod knock, but it is a completely different issue.

Lean Air/Fuel Mixture

A “lean” mixture basically means there is not enough air and too much fuel being run through the engine. This problem might occur if the car’s oxygen sensors are not working.

Bad Belt Pulleys

Believe it or not, you might hear what you think sounds like rod knock coming from an unlikely place — the engine belt. This is the flexible piece that rotates around by way of pulleys. If these pulleys are bad, then the belt can slip out of place and create these noises.

Since there are several causes that can be responsible for the noise, you need to determine if it is safe to drive and how much the repairs will cost. Your next step is to get your car into the shop as soon as possible.

Is it Safe to Drive With Rod Knock?

In theory, your car is going to gradually get worse if you discover the noise is actually rod knock. Although you can drive it to the shop if you just started noticing the noise, you should not be driving it daily or for long distances.

It is the type of problem that will not go away on its own. The rod knock will eventually worsen to the point where it can potentially damage your engine permanently. This takes a small problem and turns it into a much larger one if you wait too long.

Even though it might be tempting to just ignore this noise and put off getting repairs done in a shop, the problem can turn catastrophic before you know it. This is when it becomes unsafe to drive because your engine will fail, which means it can stop working while you are driving. You definitely should not put it off if you can help it.

Although your car’s engine probably will not stop working immediately after you hear the rod knock noise, it only has about six months left before the engine fails. Keep in mind that this is also not a guarantee. It can happen a lot sooner, but you should not expect your car to continue running for much longer than six months.

How Much Does It Cost Fix a Knocking Rod?

To repair rod knock, you likely have to replace multiple parts. Since they have become worn down and are banging together, this can create damage even before the knocking sound is noticeable. You will typically need to bring it into the shop to be assessed for which parts are okay and which ones need to be replaced.

The mechanic will have to rebuild your engine and pull these clanking rods out. They will likely also have to replace the bearings since the wear and tear is the cause of the problem. There is also a chance that these rods being misplaced have also damaged the crank surface.

It is important to have a financial safety net when you own a car. In case of a rod knock issue, the rods themselves can cost between $2,500 to $4,000 to replace. This is not a small price tag, so having money saved up in case this issue arises is very helpful.

Remember that the rods might not be the only parts you need to replace. You will be looking at upwards of the quote above, plus you need to take labor into consideration. Getting the issue checked out right away is always going to result in a lower cost and a problem with your car that is still fixable.

These prices are not set in stone because car repairs are typically more complex than you think. Since there are so many moving parts working together, one small disruption can cause a huge problem. Only through a professional opinion will you get a quote that is accurate.

Being knowledgeable about cars might allow you to identify if your car has rod knock or not, but it is still advised to get a professional opinion since there can be multiple damaged parts. Rod knock is definitely not something to create assumptions about since it is your engine being put at stake.

The Overview

Rod knock is a very specific problem that occurs when your bearings become worn and the rods begin bumping around. This sound is something you will definitely notice while you are driving, and it can evolve into a very costly and dangerous issue if it is not addressed soon enough.

There are several other issues that can cause the same type of sound, but only worn bearings are responsible for rod knock. It is always a good idea to have a financial safety net to cover the cost of these repairs and to get a professional opinion when you start to notice the sound. By following these guidelines, you will be able to save your engine before unfixable damage has been done.

See also: How to Reduce Engine Noise in the Cabin

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