Engine Rattle On Startup (All You Need To Know)

If your vehicle’s engine is making that rattling noise, then there could be something wrong with your vehicle. A vehicle engine does not always sound smooth, but if it makes that rattling noise, there can be plenty of causes why your engine is doing that. 

If the engine of your vehicle is making that rattling noise during startup, idle, or if you are accelerating, then you might be having a faulty serpentine belt tensioner, a loose timing belt, a loose bolt on the mounting bracket, rusty or a broken flexplate, a loose fan blade, a faulty harmonic balancer, an engine knock or pinging, or a low level of your engine oil. These are the possible reasons for having an engine rattle on startup. 

Some car drivers might ignore this, but you should always have your vehicle on check for unusual sounds coming from your engine for your safety. As a car driver, you should know the basics of why your engine would rattle on startup. 

That is why we have made this article. In this article, we will talk about the reasons why your engine would rattle on startup. So without further ado, let us talk.

Engine Rattle On Startup

Why Does My Car Engine Rattle When I Start It?

A car engine does make its sounds, and it is not always smooth. The engine of a vehicle has many moving parts, and these moving parts make their noises and sounds. Of course, these sounds can be expected. But if your engine is making that rattling noise, these are the possible reasons behind the unusual sound.

1. You Might Be Having A Low Engine Oil

If your engine is making that rattling noise, your first suspect is that you may be having a low engine oil. If your engine has low oil, this can cause a rattling noise. There will be very poor lubrication to no lubrication at all for the engine components if you do not have enough oil. 

So you need to check your engine oil level and add oil as needed. If the oil level in your engine is shallow and the engine is rattling even after you added oil, there can be permanent damage that will occur. 

A replacement will then be needed depending on the part that was damaged. But you can just easily top up your engine oil.

2. You Might Have A Cracked Or A Broken Serpentine Belt

Diesel vehicles or gasoline vehicles have their serpentine belts. Some vehicles have one. Some vehicles have two, and some vehicles have three. 

The serpentine belt has a job to drive your alternator, your waste pump, and your conditioner compressor. Sometimes, your serpentine belt can be mistaken for a timing belt. What is different is that the timing belt is running the engine camshaft, and most of the time, you might not see it because it is hidden under that protective cover while the serpentine belt can be visible and visible. 

If your serpentine belt breaks, it can cause a rattling noise on your engine. Your vehicle will not be able to drive, and you might even have to call a tow truck. 

Also, if you drive your vehicle and have a broken serpentine belt, your engine can overheat. This is because the water pump is not working.

3. You Might Have A Broken Mounting Bracket

The third thing that could be making a rattling noise has a broken mounting bracket. A mounting bracket can support different accessories like the power steering pump compressor and the air pump, like attaching the engine to the frame of the vehicle. 

If any of these mounting brackets are broken, then the component that the brackets are holding will start to vibrate, and as a result, there will be a rattling noise. You will need to check every mounting bracket or bolt and check if there are any loose.

4. There Might Be A Broken Or A Cracked Timing Belt

The timing belt has its job of connecting the engine crankshaft to the camshaft that will allow the valve to open and then close at the right time together with the position of the pistons. The timing belt must be under a specific tension that will be allowed by the timing belt tensioner. If the timing belt or tensioner is damaged, it will get loose and vibrate. 

It will then make that rattling noise. Therefore, you must consistently change your timing belt if you think there are any cracks to avoid further damage to your engine.

5. You Might Have A Broken Flexplate

The flexplate or a flex shock device can be found in those vehicles that have an automatic transmission and those that have a function in connecting the crankshaft in the torque converter and then improving smooth running. If your car has a broken flexplate, the connection that the crankshaft and the torque converter have can be compromised, and it will not run smoothly. If that is the case, you will have to take off the flexplate cover and check for the cracks, rust, or if there are missing bolts.

6. You Might Be Having A Broken Crankshaft Harmonic Balancer

A crankshaft harmonic balancer is part of the crankshaft, and it has the job of absorbing and then reducing the vibrations from the engine if the crankshaft rotates. This is made up of rubber and metal. You can find them at the front of the crankshaft pulley. 

If the rubber and the metal on the crankshaft harmonic balance will wear off, and it gets dislodged, it will make a rattling noise and cause vibration. So it is an expendable item and could fail.

7. You Might Have A Faulty Fan Clutch

A fan clutch is a cooling system component, and it will regulate the engine’s temperature. It will engage and then disengage the engine’s cooling fan. Some vehicles have mechanical fans, and some also have electric fans, but they are both based on the engine’s temperature. 

If the engine’s temperature gets high, the thermostat will trigger the fan clutch and engage the cooling fans. If the fan clutch is broken and gets stuck in an engaged position, this will turn on the engine fans even if they are not needed and create a loud noise.  

If the cooling fans run for a long time, they will get loose and start to create a rattling noise. You have to pop up the hood and check the movements of the fan blades. 

8. You Might Be Having A Car Engine Knock Or Pinging

An engine knock or a pinging will happen if there is a mixture of air and fuel inside a cylinder, and if it is incorrect or unbalanced, it will make the fuel burn evenly. It will cause a shock wave at the wrong times and make a rattling noise. It can damage the cylinder wall also and the pistons. 

Is Engine Rattling On Startup Normal?

This will depend on the type of rattle the engine has. If it is a low knocking noise and you can hear it during idle, but it goes away if you rev the engine, then it can cause a worn or loose big end bearing. That means that the engine will need to be replaced or rebuilt. 

You might hear this sound all the time, but it will be less likely to happen if your engine is warm. If it is a high-pitched rattle that you hear in all engine seeds but goes away after startup, then it will sound like a loose cam chain. You have to change your cam chain, generally solving the problem. 

It is also cheaper than rebuilding your engine or swapping it. If your cam chain tensioner is a manual hit, it can be a matter of adjusting to remove the noise. If you hear a loud knocking or a rattling noise from under your vehicle, it can be a cause of an exhaust pipe that is coming loose and is striking the underfoot pan. 

This is a common situation on startup if the engine shakes. You might find one or more of your flexible exhaust hangers broken. So there are sounds that might be normal, but it is not normal if your engines are rattling.

Is Engine Rattling On Cold Startups Normal?

Starting for o PSI oil pressure in your stationary engine can be a surprise, and it might take a minute or two for the pressurized oil to go all around during a cold start. It is perfectly normal, though. 

The sound will go away immediately. However, if the sound continues even after the engine runs, it might be a good reason to look for any problems. 

What To Do When Your Engine Rattle On Startup?

You should know first the reason behind the engine rattle. There are many possible reasons why your vehicle engine would rattle on startup. 

You must first identify the specific reason why your engine is rattling up. After identifying the reason, you can now identify what to do for your engine rattle. It might require replacement or repairs.


In summary, an engine startup is not always smooth, and it has different noises. These noises can be expected. 

However, there are noises like engine rattle that are not normal. There are many different things why your engine would rattle.

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Image credits – Canva

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My name is Hank, and I've been in the automotive industry for 27 years. I've been working in my own auto repair shop for the last 13 years, and now I want to help you here, on my blog. Let me know if you have any questions. Read more