I have compiled and investigated the most common reasons why the engine may rattle when idle. In short, here are the most commonly occurring problems that cause engine rattle:
- Timing chain problems
- Valve timing solenoid problems
- Damaged engine block
- Loose undercarriage protection
- Damaged engine mount
- Worn-out exhaust pipe mount
- Broken turbocharger
Understanding the engine rattle problem
First of all, we need to understand what the engine rattle is and how and when we hear it. Without this, you can spend hours and even days troubleshooting your car and still you will not be able to find the actual reason.
Your engine may rattle in certain conditions like when it’s cold or when it’s heated to the working temperature, or when you are accelerating. You may hear the rattle from under the car or in the upper part of the engine. The rattle can be noisy or quiet, it can resemble the sound of metal parts hitting each other, etc.
Here is what you should check before we start talking about the actual reasons for this problem:
- When does your engine start rattling? Rattle in cold engines may often show that the cylinder block or pistons are not healthy. Hot engine rattle may tell you about issues with valves.
- How persistent is the rattle sound? Constant rattling may tell you about problems with the timing chain or a fatal situation with the pistons.
- How loud is the rattle? If it’s very loud and you can hear it inside your car and outside it, the chances are some outer parts of the engine are in charge of the problem. For example, the heat shield on the exhaust system may rattle.
- Where exactly do you hear this rattle? You should investigate this problem and understand what part of your vehicle is rattling more than others.
After you answer these questions, you will have much more information to help you locate the problem and eventually solve it. Also, you may need to think of what you repaired in this engine within the nearest month. Very often, the problem happens because some of the parts weren’t fastened very well or some bolt wasn’t torqued properly.
Now we can move on to talk about actual reasons and how to solve these problems without breaking the bank.
1. Timing chain rattle
Timing chains are often said by manufacturers to last as long as engines do. But in reality, these chains may fail after about 80,000-120,000 miles. Before the timing chain fails it may stretch. Actually, timing chains stretch over time and there is a special tool called a tensioner that helps the system balance the timing chain stretch. But if the chain is stretched more than the tensioner can compensate, this will obviously lead to rattle.
Usually, this rattle is heard from inside. At first, it’s not very loud but pretty consistent. After some time, the rattle becomes louder and the chain may even jump. In most engines, timing chains are located on the right side. So, you will hear the rattle right from that side of the engine.
If you hear the timing chain rattle, it means that you should immediately replace the timing chain and the tensioner. Otherwise, the chain will stretch even more and jump. If the timing chain jumps, in most cases, your engine will be destroyed – it will have problems with valves and pistons. Repairing your engine after such an occasion is not always possible.
I recommend replacing the timing chain at about 100,000-120,000 miles, even though car manufacturers and dealers may tell you that the timing chain shouldn’t be replaced at all.
2. Valve timing solenoid rattle
The majority of modern engines will have a valve timing system at least in one camshaft. I will not dive into this technology because it will take a lot of time but you should know that the valve timing is controlled by special solenoids. After some time, these solenoids go bad and get stuck and this may cause the wrong timing of the valves.
So, the valves may start rattling as well as the solenoids themselves. One of the possible solutions to this problem is to clean the valve timing solenoids. But in some cases, they may only be replaced by new ones.
If your valve timing solenoids are in charge of the rattling noises, there also could be problems with the performance of your engine like power loss or bad gas mileage. It’s not really hard to clean the solenoids so you should check this possible issue in your engine before you agree to any more complicated repair.
3. Damaged engine block and pistons
Unfortunately, the engine rattle may show up because of the damaged engine block or damaged pistons. The majority of modern engine blocks are made of aluminum alloys to make them lightweight. But this material is less durable than cast iron which was used before for engine blocks and other components of engines.
If an aluminum engine block is overheated, it may change its shape and in the worst-case scenario, it can even crack. Even tiny cracks in the engine block or in the piston can lead to fatal engine damage. It may start leaking antifreeze, oil, and fuel and it may start literally falling apart.
If this happens to your engine, you better react immediately and have the engine inspected so that a professional mechanic would tell you if it’s still possible to repair it and save its life.
Pistons can also be damaged because of overheating or just because of the age and mileage of the engine. In some engines, pistons may rattle a little bit even when they are new and it’s OK. One of the examples is the 1.6-liter engine in the Ford Fiesta in the American market.
4. Damaged engine mounts
If one of the engine mounts is damaged, the engine will slightly change its location under the hood and will start vibrating heavily. One of the possible consequences of the malfunctioning or ruined engine mount is the rattle.
One simple way to check these is to open your hood, stand right in front of the vehicle so that you could see the engine, and ask someone to start the engine. If it shakes like crazy, you may say for sure that one of the mounts is broken.
Replacing the engine mount is certainly not a DIY job. Also, you should remember that it’s always best to buy an OEM engine mount because aftermarket mounts are not really durable and may fail a couple of months after you install them.
5. Broken turbocharger
Turbochargers in most modern engines are really tender and they need proper oiling and very clean air to function properly and for a long time. If something is wrong with the turbocharger, one of the common signs of this is rattling.
The turbocharger consists of a tube that the air comes through and the metal impeller that sends this air through to the engine. This metal impeller may start shaking and hitting the walls of the tube it’s located in and this will most likely convert into the rattling sound.
Broken turbochargers can be repaired but, in most cases, the price of the repair will more or less be the same as the price for the replacement of the turbo.
6. Exhaust pipe mounts
Your exhaust pipe is mounted on special rubber mounts that hold on prepared metal hooks welded to the car body. The other side of these mounts holds the exhaust pipe, the muffler, the catalytic converter, and other parts of the exhaust system.
When you are driving on the good road, these mounts basically don’t work and are not wearing out extensively. But when you drive on bad roads or when you are off-roading, these mounts are stretched and they get quite a lot of damage. After some time, these micro damages become real cracks and holes that just tier these mounts and destroy them.
If one of the mounts is broken, your exhaust pipe may start heating the car body from the downside. Given the engine always vibrates, the exhaust pipe may create something like a rattling sound.
Fortunately, replacing these rubber mounts is not a very hard task and you can obviously do it on your own – just buy the OEM mounts so that they could last longer.
7. Splash shield bolts
Some vehicles have plastic undercarriage covers under the engine and those will never create a metal rattling sound. But in other cars, you may find a metal splash shield or undercarriage cover. This part serves as a good protection for the engine from all kinds of road debris and also off-road obstacles that you can hit your engine over.
But these covers are not immortal. Once you hit them with something hard and heavy, they may change their shape, or one of the bolts that are holding them may go bad. If this happens, one of the sides of this engine cover will have some free play and will start hitting over the car body creating a rattling sound.
After some time, the damaged undercarriage cover may change its shape even more and eventually create dragging sounds because it will literally start dragging on the road. If this is the case in your situation, you may just take the undercarriage cover off the car and have it mounted back by a professional the next time you are in the dealership or in the repair shop for some maintenance.