What is Rod Knock and How Do You Fix It?

Rod knocks refer to an engine’s rhythmic thumping sounds as you drive. It commonly manifests when you rev up the engine or remove your foot from the pedal.

This banging noise is created by rods hitting the crankshaft when there’s too much clearance in their respective bearings. These rods aren’t supposed to clang and rattle against the crankshaft. If you hear this noise, it’s possible that the rod bearings are damaged or worn.

Is Rod Knock Dangerous?

If your vehicle exhibits engine knocking, it’s important to address it immediately. Such sounds from the engine may indicate problems that can worsen and require expensive repairs if left unchecked.

In some cases, rod knock indicates poor lubrication of the engine’s moving parts. Issues causing rod knock can potentially make an engine overheat, leading to serious engine damage.

Though you can technically drive a vehicle with rod knock, it’s not recommended. If you hear knocking from within the engine, it’s a good idea to pull over and bring your vehicle to the nearest mechanic for diagnosis and repair.

What Causes Rod Knock?

It’s arguable that the most common cause for rod knock in engines is worn rod bearings, however, this problem can also be caused by insufficient engine oil. Contaminated engine oil is another major factor that leads to rod knock.

Worn Rod Bearings

One of the most common causes of rod knocking is worn connecting rod bearings. When these bearings are misshapen or damaged, the connecting rod becomes loose. This makes them rattle and bang against the crankshaft.

Insufficient Engine Oil

Engine oil plays a crucial role in your vehicle’s engine by helping different components move. The oil lubricates all moving parts, including the rod bearings. If there isn’t enough engine oil in the vehicle, rod bearings and other moving parts dry out and get worn down by friction.

Contaminated Engine Oil

If you don’t change your vehicle’s engine oil often enough, it might get contaminated by water, metal particles, and other unwanted substances. Contaminated engine oil doesn’t just lead to rod knock – it can also lead to other engine complications that might lead to serious (and permanent) damage.

Issues Commonly Confused with Rod Knock

Strange engine noises aren’t always caused by worn rod bearings. Issues like failing tensioner belts, malfunctioning knock sensors, and engine detonations may be mistaken for rod knock.

Bad Tensioner Belts

Though bad tensioner belts and pulleys don’t cause rod knock, these components can produce rattling noises in the engine. If you hear knocking from inside your engine, inspecting it or consulting a mechanic before attempting any fixes is a good idea.

Knock Sensor Malfunction

If your vehicle’s knock sensor malfunctions, it might struggle to determine whether or not fuel is being burned fully. Improper combustion can cause vibration and knocking noises inside the engine. These noises can easily be mistaken for rod knocks.

Engine Detonations

Engine detonations can easily be mistaken for rod knock sounds. These detonations are often caused by engines that run lean, which means there isn’t enough fuel and too much air in the combustion chamber. Detonation knocks sound identical to rod knocks.

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How to Fix Rod Knock: DIY or Hire a Mechanic?

Since repairing or replacing engine components is a delicate affair, it’s best to leave such procedures to trained mechanics.

A professional will be more equipped to inspect each rod and its respective bearings before draining the oil and checking the oil pan. If there are any shiny bits in the oil, there’s a good chance they’re from the damaged rod bearings.

The mechanic will then inspect other components affected by rod knock, such as the crankshaft and the fuel injection system, and make the necessary replacements. You can expect to spend between $2,000 and $7,000 to fix rod knock.