Replace My Car Or Auto Engine / Motor? Understanding Pinging, Knocking & Other Sounds in my engine.
This post is applicable to petrol and gas / LPG engines. (The diagnosis of diesel engines is different and will be the subject of a further blog post.)
So there is a strange noise in your car-auto engine or motor? Perhaps you had heard it before but wanted to ignore it? A noise like this can be very annoying. It is possible to diagnose what is going on, with some understanding of the the sound and what the various sounds may mean. Let’s go through some of the noises and their possible cause and solutions.
So what does the engine-motor noise sound like?
Not all engine knocking sounds are the same. It’s a little bit like when your doctor listens to your chest for the sound of the heart. It’s exactly the same principle. The doctor is listening for tell tale sounds that may indicate the heart mechanics, including valves, are not opening and closing as they should be. How amazing is that? A skilled ear can make quite an accurate diagnosis! So what does a skilled ear listen for when diagnosing an engine knock. If you imagine that there can be a tonal scale to the knock and its like tuning a piano. There are keys that are high pitched and there are low pitched or deep sounding keys. With various problems in a motor that cause a knock there is also the very high pitched metallic sound right down to a dull hard knock. We are going to categorise these sounds into two possible categories and keep this at the basic level:
Knocking implies a much stronger sound. A mechanic that might say that an engine has an ‘engine knock’ is referring to a strong sound almost like you were hitting a very solid metal object with an equally hard metal hammer. If the sound is like that; very low in tone, it could be a very bad sign. This indicates that the engine has something possibly going very wrong. An engine has a lot of moving parts, they are covered in a film of oil where they come into close contact. The parts must also have the correct tolerances to function properly. If something starts to fail, it will usually be associated with some kind of warning sound. Here are some of the possible points of failure in an engine that will often cause a ‘knock’:
Big end bearing failure
Engine oil pump failing
Wear gets to a point that engine oil pressure cannot be maintained
Valve sticking and hitting the piston
Broken piston or valve
And of course many others
So as we can see there are lots of points for failure. Any one of these, will generally be associated with a pretty definite engine sound. Usually something broken will sound pretty loud and become more pronounced under revs even with no load. Usually getting much, much worse as you pedal the accelerator. Of course there is cases where these sounds are not so pronounced even in a motor that is failing. But generally they get worse progressively and without too much time. If you start hearing a dull, deep knocking sound in any motor the first thing you should do is look for any engine warning signals on your interment cluster. Immediately stop the motor. Once stopped, you should check the engine oil level carefully. If you are driving, of course pull over where it is safe to do so. The procedure for this is important to get a good reading of your oil level, don’t short cut it as it is possible to think your oil is good when it is indeed low:
Stop the engine
Pull the dipstick
Clean it or all oil, with a lint free rag (Observe the high and low points on the stick for future reference, they are usually stamped into the stick)
Insert the dipstick and count to 10
Pull it out again carefully without touching any part of the car or your hand on the reading end
Check the low and high points for oil mark
If the oil is not bang on the high point, add oil in small amounts to get it to the high point following steps 1-5 until it is exactly on the right mark. NEVER over fill the engine with oil! It can damage the motor.
If the engine oil was too low, it can cause the knocking noise. It can also do major damage to the engine. So if that was the problem, you need to get the engine checked out for the following:
Wear, creating bypass where the oil gets burned up or blown out in smoke
If the oil level is ok and the knock is still there. Then there may still be some other major problem. If the knock is getting progressively worse or perhaps is worse under load then these may also not be good signs. It is best to get the engine checked out by a professional. If you are pretty sure that you need a replacement engine then you can check out our preferred suppliers on our partner page to get some help. This company has a lot of low mileage engines car parts and are happy to help.
What if the sound is not so loud and is not so low in tone? If it almost sounds like the hammer is a much lighter one and it is tapping very fast on aluminium. If this sound is also not always there, but can be heard under load or high revs. It can be something quite different. It may be ‘pinging’.
It can be a big mistake to over react to pinging. So let’s summarise the sounds and conditions of pinging.
The sound is more like a higher pitch tap of light metal on metal. It can even sound like something is rattling or lose in the motor. It can be much worse under higher revs and under load. It may be completely non existent at low revs with no load on the engine. The sound may also get worse as the engine runs in very hot conditions.
So what is pinging caused by?
The pistons in the engine are forced down in the cylinders by the explosion of fuel within the cylinders. The idea is that the triggering of this explosion at the right time is critical to the motors proper functioning. You can imagine what would happen if the explosion happened too soon? It causes the rising piston to hit a wall of gasses. This is called pre-ignition. In simple terms causes the piston to ‘rattle’ in the bore and slap the sides of the metal bore as it rattles. It results in pinging. What causes this?
Here is a picture of what is going on inside the motor.
In general a couple of things:
Poor quality fuel
Bad engine timing
How much of an issue is poor quality fuel?
Well it’s a big one, if you are located in Australia like me. The quality of fuel we get is massively variable. This can be a clue to your problem. If you recently filled up your fuel tank, then very close to this event the ‘pinging’ started; it is a dead give away. Often we get fuel that has been sourced from lower quality sources. These fuel sources may have lower ‘octane’ levels than what your car can handle. This can lead to pinging. The other thing can be accidentally putting the wrong fuel into your car. Some cars are mean’t only to be run on the higher octane or premium fuels. This will cause these higher specification engines to have difficulty adjusting to the lower octane fuels. (Octane level is in simple terms how much explosive force in the fuel. The higher the octane, theoretically the higher the energy output for the same amount of fuel.)
Not all engines are the same. Some are far more prone to this engine pinging issue. For example, I have a BA Ford Fairmont and this vehicle is very prone to the affects of pre-ignition or pinging, when it gets bad fuel and when its a very hot day. This combination seems to really bring on the issue. It is nearly impossible to accelerate and put the car under load without hearing some pinging. The car has been for multiple tune-ups and it seems that the engine is not able to adjust its computer enough to correct the ignition to the right point. Ideally pinging should not be left unattended to. Obviously if your pistons are rattling in the bores constantly there is damage done to the motor. The engine will also not be developing full power. So get the engine looked at by a professional mechanic. Or of course change your fuel if you think that could be the cause. I would also encourage you to experiment with various fuel providers. If you have a vehicle you think may need high octane fuel, make sure you give it only that.