Rod Knock Symptoms (Causes & Solutions)

Do you want to know about rod knock and the various rod knock symptoms so as to know when you might have a rod knock on your engine? If so, you are on the right page.

An engine problem is among the worst problems a vehicle owner can encounter. If an engine has issues and the engine is not given attention for a while, it becomes more difficult and expensive to repair. An example of one of these engine issues is the rod knock.

Engine problems can only be fixed by someone with adequate knowledge about the problem. For this reason, it is necessary to know about issues affecting the engine and other parts of a vehicle.

For vehicle owners that know little or nothing about rod knock, this article’s objective is to take a closer look at rod knock, Rod knock symptoms, causes, and how it can be fixed. So, do well to read and understand the content of this article.

A connecting rod is usually attached to the crankshaft and piston. Also, the bushing is referred to as a bearing between the crankshaft and the connecting rod.

The bearing is made with a metal that is not as hard as the ones used in making the connecting rod and the crankshaft.

Normally, vehicle engines have a clearance tolerance to properly allow the bushing slot into the crankcase journal. This clearance aids the flow of engine oil on the metal surface, which prevents it from wearing out quickly.

However, as time goes on, the bearing found between the connecting rod and crankshaft starts wearing off, which results in rod knock.

In any situation, normal wear does not usually cause rod knocks due to the distance (hundreds of thousand miles) it will take the bearing to start wearing off. Mostly, rod knocks occur as a result of premature wear.

Now, the question arises, “What causes premature wear?” Premature wear usually occurs when the engine oil is dirty, when the oil level is low, when oil pressure is low, or when the engine overheats, among other reasons.

Also Read: Engine Knock on Startup then Goes Away (Causes & Solutions)

What Does Rod Knock Sound Like?

Rod knock is easy to notice if it is not happening for the first time. The engine usually makes loud bangs when it is revved up and the leg is taken off the accelerator. This sound usually comes up immediately after taking the leg off the accelerator.

Rod Knock Symptoms

Rod Knock Symptoms

If a vehicle’s bearing wears out, there are two common signs that show that the vehicle is having a rod knock. These signs are:

1. Knocking Sounds

The main and obvious signal a vehicle with a rod knock problem gives is the knocking sound. A loud bang is usually heard immediately after the vehicle is started.

The noise would increase as the load increases on the vehicle or as the accelerator is pressed down.

2. Low Oil Pressure

When a vehicle’s bearing has started failing, the oil pressure becomes less than normal. It is usually seen immediately after the vehicle is started.

The Check Engine Oil signal may even show up on the dashboard, informing the driver about the level of oil pressure. If the sign does not show again after a while and oil pressure goes back to normal, this could be a big sign that the bearing has worn out or is damaged.

Causes of Rod Knock

Rod knock usually occurs when the bearings on the connecting rod wear out. Rod knock occurs as a result of just one problem. However, a number of factors could be responsible for this problem and show signs like that of a rod knock.

Some reasons why rod knock may occur in a vehicle or show signs similar to that of a rod knock:

1. Worn Bearings

The sole reason why a rod knock happens is when the bearings wear out. When pistons move around in the engine of a vehicle, they make the crankshaft spin, which sends power to the tires. The bearings ensure that pistons move smoothly and in a calm manner.

Although, bearings may get worn as time goes on and may also go out of their place or position. When a bearing wears out, piston rods begin to have a rough contact with the crankshaft, which results in a unique knocking noise.

There is only one way to fix this: To change the bearings, which run deep in the engine.

2. Low Octane

Detonation knocks do have a similar sound to a rod knock. The fuel and air mixture ought to burn in one detonation within every cylinder. Although, the detonation sound is only produced when the mixture detonates in multiple places at once, which is why the knocking noise is heard.

A detonation knock may occur when the vehicle has an octane that is not high enough for the engine. If a vehicle has a performance engine, it usually requires a high octane rating more than a lot of vehicles.

With a high octane, the mixture burns uniformly, which prevents that knocking sound from being made.

This issue can be fixed without too much difficulty. All that is needed is to start using fuel with higher octane when filling the vehicle subsequently.

3. Poor Engine Timing

Poor engine timing could also be the reason why the detonation knock occurs in a vehicle. The timing talked about here is the moment at which the spark plugs ignite. The computer regulates this timing.

With poor timing, spark plugs will not ignite at the moment they ought to, which will result in multiple detonations in the cylinders. This is why a detonation knock occurs. To fix this problem, fixing the timing becomes necessary.

4. Lean Air/Fuel Mixture

A small quantity of air and fuel mixture is another reason a detonation knock may occur. This issue usually occurs due to bad oxygen sensors, fuel injector failure, a defective fuel pump, or a malfunctioning mass airflow sensor.

A lean mixture is when the amount of fuel is really low while there is excess air. If an adequate quantity of fuel is unavailable, the mixture will not burn as fast as it should, which will cause several detonations.

6. Bad Knock Sensor

Detonation knock can also occur if the knock sensor starts to malfunction. Fortunately, this rarely happens to recent vehicles since their air and fuel mixture, fuel injectors, and timing is regulated by their computers.

Knock sensors detect any situation that causes the knock and notify the ECU, which takes corrective action immediately. Hence, if a vehicle has a defective knock sensor, it may result in the engine knocking as the computer will be unable to know what exactly is wrong with the vehicle.

Also Read: Bad Knock Sensor Symptoms (+ Replacement Cost)

7. Bad Belt Tensioner/Pulleys

The last reason which may cause an engine knock is something that does not constitute part of the engine in any way. An accessory belt without the necessary tension will create a sound similar to an engine knock.

While the engine turns, the belt also turns with it. The belt is linked to several pulleys in the engine bay, which are supposed to be pulled in the right manner to enable them to work smoothly without any disturbing sound.

Once the belt becomes loose, it is an indication that the tensioner is not working as it ought to. Although, problems may also occur if a pulley bends.

This situation will cause clicking, slapping, and rattling sounds that can easily be mistaken for an engine knock. To solve this problem, change one of the belts, pulley, or tensioner.

Rod Knock Symptoms

How to Fix a Rod Knock

Rod knocks usually indicate that something has gone wrong with one or more interior components of the vehicle’s engine.

As stated earlier, many factors may cause a rod knock. Some repairs come at a very high cost, while others are not so expensive. If this happens, it does not mean the vehicle’s engine can no longer be repaired.

However, going to a mechanic or a car dealer for assistance is essential. Taking these few steps can reduce the sounds and could even stabilize the engine before taking it out for a thorough repair.

Step 1: Carry out Oil Change service

Get under the vehicle and position a container straight under the sump bolt. Get a small wrench and socket size. Find the sump bolt on the crankcase, open it and take out the oil.

Take out the oil completely and put the bolt back in position (draining plugs are also known as sump bolts). Tighten the bolts to the specification of the manufacturer.

Take out the oil filter by holding it with a filter wrench, then turn it clockwise. Put a new filter in its place and tighten it as specified. Replace the motor oil with another one of a similar viscosity rating or any recommended oil.

Continue to check the oil while pouring the new one if uncertain about the number of quarts required by the engine. Four-cylinder engines usually take 4 to 5 quarts.

Step 2: Remove the Crankcase and Inspect the Cod Rod Bearing

A loose connecting rod cap will make the vehicle produce a knocking sound. Check the bolts keeping the connecting rod in position with the lid. If they are loose, tighten them. Try to inspect the connecting rod bearing and change it if necessary.

Step 3: Pour Fuel-Injector Cleaner Into Your Gas Tank

Dirt and particles could gain entrance into the fuel tank while refilling the tank at a gas station. In the process of

passing fuel into the engine, the fuel pump will also send the dirt and particles contained in the fuel tank to the engine, and this will cause the engine to knock.

If the fuel injection system is cleaned, it will clear the debris in the system and solve this problem. Using a fuel injector cleaner would be wrong in vehicles made years ago, which have carburetors and not fuel injectors. Rather than doing this, carburetor cleaners fit better and should be sprayed on carburetors.

Check out this video for more tips on how to fix rod knock

Rod Knock Repair Cost

Reproducing a rod knock problem comes at a high cost of about $2,500 or more. Although for some vehicles, like the Subaru Forester, repairing the connecting rod cost a lot and can take up to $5,000 or even more, though this price includes labor fees.

To replace the bearing of a connecting rod is quite a difficult task. This difficulty is due to the defective component being rooted deep in the vehicle’s engine. This means there will be a few other parts that need to be changed asides from the bearings.

Some parts are bolts for the cylinder head, seals, and engine gaskets. Also, the cooler lines of the engine require flushing.

In certain instances, the crankshaft, connecting rods, timing chains, pistons, and bearings may need to be replaced. Considering these additional parts, replacing the whole engine may be a better option.

Also Read: Rod Bearing Replacement Cost

Tips to Prevent Rod Knock

There are quite a number of ways to prevent the engine from making the knocking sound. These ways include:

  1. Topping up fuel tanks at reliable stations
  2. Not using fuel with low octane ratings
  3. Replacing spark plugs from time to time, as instructed by the makers
  4. releasing engine throttle immediately once you hear a knocking sound
  5. Use effective fuel additives to take out carbon deposits or prevent their accumulation in the vehicle.

Frequently Asked Questions – Rod Knock Symptoms

Can you drive a car that has rod knock?

When the engine produces a rod knock noise, it is an indication that such a vehicle ought not to be driven. If a vehicle makes a rod knock sound, it may cause the engine to fail while driving.

What happens if you have a rod knock?

A rod knock indicates a serious problem with the engine’s engine (meaning there is a problem with how the engine works.) If a rod knock is noticed, it is better to swing into action immediately as this problem does not fix up with time. Change the bearing and fix any other components that may cause the sound.

How long can an engine last with rod knock?

Immediately an engine starts knocking, the rod can break without warning. The breakdown could be immediate, or it could take even six months before it happens. In the long run, the engine blows, and the vehicle’s occupants will become stranded.

Can a rod knock go away?

Rod knocks do not resolve themselves unless it is fixed. A total change of the oil could fix this. Pour 4 quarts of good oil with a bottle of oil stabilizer.

How much does it cost to fix rod knock?

If an engine rod becomes bad, it may be responsible for the engine knock problem. This noise is caused by a collision between the bearing and crankshaft journal. As this problem is difficult to repair and other probable issues it may cause, repairing it usually costs between $2,000 to $3,000.

Can you hear Rod knock at idle?

As a vehicle idles, a weird engine sound may appear. This sound is called a rod knock. It usually comes in the form of banging noise, loud enough to pause a heartbeat as the driver starts to think of the cost of an engine repair.

How does Rod knock start?

Rod knocks are deep, loud rattling noise the engine produces. It is usually caused by damage or wear. When the connecting rods of a vehicle in the bearings have too much clearance, it affects the movement. When pistons switch directions, metal contacts metal and make the knocking noise that is heard.

Does rod knock get louder with RPM?

Banging sounds that occur when a vehicle is started but resolves itself in no time could indicate early failure. Piston hitting the walls of the cylinder and wrist pin knock becomes persistent after the engine gets warm.

Conclusion – Rod Knock Symptoms

A rod knock is actually among the worst vehicle issues that may occur. However, it is usually considered an issue that cannot be resolved. Hence, when vehicle owners begin to hear the knocking sound, many conclude on the spot that their vehicle is about to die.

However, the reality is that a rod knock is an uncommon issue. Although, the knocking sounds coming from the engine may be common. This means that rod knock symptoms are not unique to a damaged rod only. It could result from a little problem like the engine oil level being too low.

Hence, there is a need to know how this problem can be detected. Going through the few easy solutions discussed earlier could help take care of the situation. After this, if the sound remains persistent and the source is unknown, having a mechanic check the vehicle will be the best in this situation.

Scott Greene is a seasoned automotive technician for over 5 years and has been deep into advanced automotive diagnostics for a couple of years. He Loves writing about Automotive Diagnostics and Repair, Trouble codes, Buyer guides for various car parts and accessories, and lots more. 

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