A Whole Lot of Noise: The Truth Behind What Causes Engine Knock

Engines make a lot of different noises, but it’s the knocking which often stresses drivers out and leads them to make an expensive mechanic’s visit. There’s more to engine knocking than impending engine failure, though, and just because the noise sounds terrible, that doesn’t always mean it is. Here’s the truth behind what causes engine knock, plus a few simple ways to remedy the knocking.

What Does it Mean When an Engine Knocks?

Do you need to shell out for a complete engine rebuild or merely finance a small repair? It’s hard to know when your engine starts knocking whether it’s a severe problem or a minor annoyance. Typically, the engine knocking means the car needs some attention. But it will take a bit of investigation to determine whether it’s a simple solution or a complete engine overhaul that will fix it.

Types of Engine Knocks

A single, loud knock can mean something just blew up under the hood. But when it’s a continuous, regular noise with no apparent source, it’s sometimes hard to discern what type of knock you’re experiencing.

A detonation knock is when something blows up or cracks under the hood. The detonation type knock may even sound like a part blew off—which is also possible. You may find your vehicle dies after this happens, or starts making other types of noises, too. In this case, it’s vital to pull over and check everything out as soon as is possible and safe.

On the other hand, a crankshaft knock tends to happen when you accelerate or are working the engine particularly hard. Valvetrain noise can come across as clicking or chattering, and it usually happens at lower speeds but fades as you accelerate.

Piston ring noise often sounds like tapping or ringing—a metallic tone—and can happen with broken piston rings, low tension, or even worn cylinder walls.

But in addition to these specific types of knocks, which can indicate a need for significant repair, there are also minor knocks that crop up over time and become more and more noticeable. In many instances, you may not notice the knocking until a passenger mentions it, simply because you become accustomed to the noise.

Thankfully, this type of knocking isn’t usually an emergency. But it’s still important to understand what causes engine knock and how to fix it.

Why Engine Knock Happens

You’re driving down the highway when suddenly, your pickup truck engine starts making a knocking sound. Do you assume it’s past due for a checkup or decide that it’s probably time for a trade-in? Or maybe you think it’s your engine rebelling against the low-quality fuel you just purchased? The answer is it could be any of these things.

Skipping Regular Maintenance

Depending on the type of engine knock (whether it’s a true knock of metal on metal or simply a pinging noise), it could be due to skipping regular maintenance. If it’s a newly purchased vehicle (whether new or used), it’s possible the maintenance hasn’t always happened on schedule.

Checking a car’s vehicle history report before purchase typically tells you whether it has seen regular maintenance. But unfortunately, you don’t always know the precise history of your vehicle—or maybe you are the owner who has neglected standard upkeep.

Regardless, skipping regular maintenance can lead to broken or loose parts flip-flopping in the engine compartment. Of course, that’s not the only cause of engine knock—just one potential explanation.

How to Fix It:

Engine knock from lack of regular maintenance is more common in older vehicles, but a trip to the repair shop can often help. Costs associated with vehicle repair vary widely, but regular upkeep is often more affordable than complete engine rebuilds or other drastic measures due to neglect.

Low-Quality Fuel

Some drivers assume that higher-priced fuel is a scam and that all fuel meets minimum standards, so any type is adequate. But for some vehicles, the quality of the fuel can make a significant impact on regular performance.

High-pressure engines (and often the more complicated ones) require higher-octane fuel, so skipping this recommendation in favor of saving money at the pump only leads to knocking and repair bills later. A high-performance engine needs higher-octane fuel to avoid prematurely igniting the fuel before the spark plug does.

How to Fix It:

If the vehicle manufacturer says to choose higher-quality fuel, doing so is one way to help mitigate engine knock in your high-performance vehicle. Even in typical cars and trucks—not necessarily high-end models—using better quality fuel can help preserve engine life.

Also consider the type of fuel you purchase and whether there are additives in the formula. If you notice your engine knocking after filling up with fuel from a particular gas station or with a certain brand of gas, it’s worth noting.

Engine Deposits

Another harmful side effect of cheap or low-quality fuel is that it can leave buildup inside your engine’s cylinder walls. Deposits block normal engine functions, clog fast-flowing channels, and raise compression. Blockages like these can cause knocking, mainly as pressure builds, and can even lead to total engine failure if you don’t address the issue.

How to Fix It:

Once you confirm that engine deposits or carbon buildup are responsible for your engine’s odd noises, a thorough cleaning can help resolve the knocking. Removing the carbon and other deposits, whether through an automotive store additive or a physical scraping process, can prove feasible even on the lowest budget.

Incompatible Spark Plugs

Using the wrong spark plugs can also cause knocking in your engine as an incorrect fit can impede performance. Engines are precise machines, meaning you can’t swap out your spark plug for an aftermarket option that almost fits because the performance will likely suffer.

How to Fix It:

Use the right spark plugs—per the manufacturer—even if they are more expensive, and you’ll likely see an end to the knocking. Even if the spark plugs are standard issue, consider checking them anyway. You should switch out the spark plugs about every 30,000 miles, and if it’s been longer than that, they could be due for replacement.

Other Solutions for Engine Knocking

If your engine is running roughly overall but it isn’t a sudden or new issue, consider some alternative steps toward clearing the noise up. Using higher-octane fuel is always a boon for your engine, according to experts, so that’s a smart (if pricey) first step.

You should also consider using an additive in your gas tank to help prevent buildup and clean out troublesome deposits. Fuel additives are typically available at auto parts stores and aren’t terribly expensive, especially if cleaner-burning fuel helps you avoid a visit to the mechanic.

Keeping up with regular vehicle maintenance is yet another fix that’s advisable no matter the age or condition of your vehicle. Standard oil changes, multi-point inspections, filter changes, and hose checks can ensure your vehicle stays running (knock-free) for years.

Costs Involved with Ending Engine Knock

If your vehicle is older and begins experiencing engine knock, you may assume it’s time to buy a new car. Fortunately, by taking the above measures, you can often resolve the issue without heading to a used car lot.

However, even a “new” used car can have engine knock and related problems. Used car values depend on market conditions, demand, and a whole host of other factors, so even a reasonably priced vehicle may still need maintenance to run smoothly off the lot.

In general, preventative maintenance is far more affordable than emergency roadside service and shop repairs. Consider the difference between a reasonable oil change at $50 versus a completely new engine for your rare Ford or replacement parts for diesel Ram trucks.