Engine Knocking Sound - What Does It Mean?

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Nobody wants to hear an engine knocking sound when driving, but unfortunately it may happen, and you need to know what to do if and when it does. A "knocking" sound is the most common engine noise, and indicates a mechanical problem that can be fixed if diagnosed correctly and early. In this article, we will look at three causes of an engine knocking sound, and what to do next. If you need more information about engine repairs and vehicle safety, trust Hansma Automotive and book an appointment today.

Engine Knocking Sound - What Does It Mean?

Contrary to popular belief, a knocking sound in your engine isn't linked to the type of oil you're using. In fact, the only engine-related noises that would have anything to do with oil would be a lack thereof, and you should have plenty of warnings before it gets to that! Here, then, are three lesser-known areas to examine with respect to an engine knocking sound.


1. Gas Octane

When your engine is working properly, the spark plugs ignite the gasoline in perfectly-timed waves that move the pistons. But if the gasoline ignites on its own before the spark plug fires - be it due to engine pressure or engine heat - it will cause a knocking sound. The gasoline's octane rating reflects how quickly it will ignite; if an engine is designed for premium (91), using a cheaper, lower-rated gas may cause the knocking. When the fuel burns this way, it burns incompletely, and the leftover fuel components and compounds cause debris that sticks to the inside of the chamber, according to How Stuff Works.

According to the Globe and Mail, experts suggest trying a lower octane gas in vehicles calling for premium (as long as higher octane is recommended but not required), and switching back if knocking occurs. Additionally, an octane booster - which can be purchased at an auto parts store - can help restore the correct octane rating and get rid of the knocking.


2. Spark Plugs

An engine knocking sound can occur if any spark plug other than what is recommended by the manufacturer is used in your engine, per YourMechanic.com

"The spark plug has a certain heat range, which means it withdraws heat from the combustion chamber. Using the wrong part can prevent it from working correctly. It's also common for engine knocking to occur when the spark plug gap is not correctly set."

If you have faulty spark plugs, your engine eventually won't start at all. Now, replacing spark plugs can be an easy job IF you have the proper tools, equipment and expertise. Check to make sure you have the following before attempting the job:

  • Spark plug wrench, or a spark plug socket and ratchet

  • Spark plug gap gauge

  • Torque wrench

  • Rag or brush

  • 5/16″ rubber hose of approximately 6″ long

Reader's Digest offers the following steps for removing spark plugs:

  1. Allow the engine to fully cool before removing the old plugs.

  2. Adjust the new plugs to the proper gap beforehand. The correct gap for your engine can be found in the owner’s manual.

  3. To avoid mixing up the spark plug wires, remove and replace one plug at a time, or use tape to label each wire.

  4. Carefully remove the spark plug wire from the end of the spark plug by pulling the rubber boot, not the wire itself.

  5. Clean off the old plug and the area around it with a rag or small brush. This will prevent any foreign material from falling into the cylinder when the plug is removed.

  6. Remove the plug by turning it counter-clockwise with a spark plug wrench.

As far as installing new ones, here's what you need to do:

  1. Make sure that the area around the spark plug port is clean.

  2. Insert the plug into the spark plug hole by hand and turn it clockwise until it’s snug.

  3. After installing the plug by hand as far as it will go, firmly tighten it with a spark plug wrench or socket.

  4. Re-attach the plug wire to the new plug. Use a twisting motion on the boot until it’s firmly seated on the top of the plug.

If you have any reservations about attempting this job on your own, leave it to the professionals and contact Hansma to take care of it.


3. Carbon Deposits

Fuel for our cars is required to include carbon cleaning detergents to help prevent carbon deposits from clogging up the cylinders. Unfortunately, some deposits still form, and when they do, there’s less room for the fuel and air to reside, leading to increased compression. With increased compression comes knocking sounds, and if the compression ratio remains off, it will affect your fuel efficiency.

The fix is to have your cylinders cleaned by a professional. Engine manufacturer Briggs and Stratton recommends that you check your cylinder for carbon build-up every 100 hours of operation, just to be safe. Most can't meet that expectation, but it's better to be safe than sorry, so drive down to Hansma today or book an appointment.

Here's a handy video that puts another spin on much of the above:

Engine Knocking Sound? Choose Hansma Automotive!

At Hansma, we offer service with a difference. We have worked hard to gain a reputation for honesty and quality work.  You can trust us to only recommend and carry out the repairs that you actually need. We will let you know what you need done and when it should be done. Our customers have come to consider us as their mechanic friend, and as such, we promise to give you top-notch service at reasonable and competitive rates. Click here to meet our friendly team, read our testimonials, and contact us today and find out about the Hansma service difference for yourself.  

We are open every weekday from 8 AM to 6 PM. Come see us at 88 Shoemaker St. in Kitchener, Ontario.

"I am a single mom and I find a lot of shops will try to take advantage of women because they think that we don't have a clue. I have found at Hansma Automotive they take the time to explain options and prices and only repair what needs to be done. A good mechanic is hard to find. I came here because they were highly recommended by a friend and haven't been disappointed" - Sue  

Read more testimonials here.



Posted on October 1, 2018 .