Why Does My Car Make a Rattling Noise on Cold Start?

Is your car making a rattling noise on a cold start? Any kind of noise can be an indicator that something has gone wrong inside the engine. But, why do cars make a rattle noise specifically on a cold start?

I will go into detail and try to explain as much as possible. So, if you wish to learn why your car makes a rattling noiseOpens in a new tab.

Why Does My Car Make a Rattling Noise on Cold Start?

Why Does My Car Make a Rattling Noise on Cold Start

Why does my car make a rattling noise on cold start? Your car makes a rattling noise on a cold start because the moment you crank your engine, there is no oil at the top of the engine. The variable valve actuator requires oil to move the position of the camshaft and without oil supply, the actuator inserts a pin and locks it in one position. Over time, the actuator becomes damaged and starts to make a rattling noise on a cold start.

Variable valve actuator uses oil to move the position of the camshaft. When an engine is first started in the morning, the oil is typically on the bottom of the engine.

However, the actuators need oil to properly work. With a sense that the oil pressure has dropped, the variable valve actuator inserts a pin and locks the actuators in place.

So, when you start your car in the morning, the actuator is in one position and it’s not moving when you crank the engine without any oil pressure up at the top of the engine.

The actuator can become damaged over time. That pin can come out or shear and produce a rattling noise on a cold start. Depending on how damaged is the pin will depend on how many seconds the rattling noiseOpens in a new tab.

Usually, the rattling noise on a cold start goes away after one to two seconds. However, if the noise is still there after a couple of seconds, the actuator is probably damaged and needs to be replaced.

What Causes Damage To Variable Valve Actuators?

The biggest cause for causing damage and eventually making a rattling noise on a cold start or any other time during driving depends on how long you go without changing your oil.

If you don’t change your oil often enough because regular maintenance can get expensive, this will lead to extra strain on the variable valve actuator, and over time, it will wear it out.

What Is a Cold Start?

Why Does My Car Make a Rattling Noise on Cold Start

A cold start is when you first turn on a vehicle’s ignition, and the vehicle has been sitting outside overnight or all day long. For most people, “cold” means under 50 degrees Fahrenheit, but it can be as low as zero degrees depending on where you live.

If you take an engine and put it in a freezer for example, and then try starting it up. It will take much longer for the engine to turn over and build enough power to get going because freezer air is much denser than outside air.

The thicker the air is, the harder your car’s engine has to work in order to produce enough power so that your car can drive down your street or highway at an acceptable speed.

So, if you leave your car overnight in freezing weather and try to start it in the morning, it will take much longer for the engine to start up because your cold engine is having to work against that cold air.

Older vehicles can take longer to start up because their engines are dirty inside and need more lubrication from the oils that get deposited there over time. This is why older vehicles can be harder to start if they haven’t been driven for several months during warm weather.

The opposite holds true when you have a brand new or nearly brand-new vehicle that doesn’t have thick built-up oil deposits in its engine yet.

What Happens During a Cold Start?

Why Does My Car Make a Rattling Noise on Cold Start

The first thing that happens during a cold start is that the engine will try to start, and then stop. This is because when a car is starting from a cold state, it uses more fuel because the engine needs to heat up before it can run efficiently.

If you own a modern luxury vehicle, you’ll see your dashboard light up as soon as you turn on the ignition, which shows that your computer system has already taken control of everything in order to comply with emissions regulations mandated by federal law.

The reason those systems kick in during a cold start is to make sure the catalytic converter gets hot enough so that emissions are reduced without having to use extra fuel.

After about thirty seconds or so after turning on the ignition, if no one has turned the key to the off position, then you’ll hear your car’s starter motor trying to engage.

This is another step that some luxury cars take in order to meet more stringent emissions requirements which state that a vehicle can’t be driven for longer than sixty seconds without starting up.

In short, because modern cars don’t start as quickly as older models, they use less fuel because it takes them less time to get going from a cold start. And that’s good news for anyone who wants their car to run efficiently and still have a powerful engine.

Is it Bad To Cold Start a Car?

Yes. Cold starting an engine damages the oil and other fluids, wastes gas, causes undue wear on the starter and battery, shortens battery life, and reduces service intervals.

If you do not let an engine idle long enough for the heat to build up or if you start it too frequently while the engine is still cold then it will never reach normal operating temperature.

When this happens unburned hydrocarbons are emitted into our atmosphere which contributes to air pollution. It also causes excess load on the alternator because of increased electrical resistance in cold parts resulting in a higher current draw than normal running conditions would cause.

The buildup of acids in gasoline results in lower octane levels than specified by the manufacturer so not only does it waste fuel but hurts performance as well.

As the engine warms up, the efficiency of internal parts increases so it takes less energy to turn them over and they wear less. The litany of problems caused by cold starting highlights why you should warm your car up before driving it.

Not only will this ensure that its operating temperature is normal but it also gets oil flowing throughout the engine which reduces internal friction and wears.

This results in better fuel economy, smoother operation, longer engine life, and more power output under all conditions. As an added bonus idling uses far less gas than constantly accelerating or cruising at high speeds because idling doesn’t require any throttle input from the driver which means no fuel is being used for acceleration or high-speed travel during idle periods.

How To Fix a Rattling Noise on Cold Start?

A rattling noise on a cold start is caused by two things – an oil problem and a break or tear of the variable valve actuator O-ring seal. It’s not normal for your car to make a rattling noise during regular driving because this means there is something wrong with the internal parts of your engine.

Since the rattling noise happens when you first start your carOpens in a new tab.

In simpler terms, you shouldn’t be running oil that’s 5W40 or 10W40 because these engine oils probably aren’t thick enough to sufficiently lubricate your engine during low temperatures.

If you use 5W40 or 10W40 oil, then changing to 0W30 or 5W30 will stop your rattling noise on cold starts because these types of oil are thicker and more viscous.

Do Cars Rattle More When Cold?

Most definitely. Cars tend to rattle more when they are cold. Some cars tend to be a bit quieter after being run for a couple of miles as the engine and exhaust system heat up and expand slightly allowing some movement in the pipes.

This loosens any bits which may have been rattled loose by the vibration from running down the road at speed even if only briefly. Depending upon how tightly things were assembled, this could last anywhere from a few days to a couple of months before it all starts rattling again – particularly after the car is turned off and everything cools back down again.

The bigger issue with cold weather is that oil becomes thicker as its temperature drops. This means that all of the little components in your engine which are suspended on a film of oil will sink lower into the crankcase and get closer to whatever they’re bolted or clamped to.

When this happens, there is increased pressure between the moving parts and any nearby objects and this can cause them to rattle.

I did some research and it turns out that automakers do take note of whether their cars tend to rattle more during colder months. It’s just another one of those things that we consumers would never know unless somebody told us!

Igor Iwanowski

I am a certified Automotive Service Excellence (ASE) mechanic since 2018. I specialize in Brake systems, dashboard warning lights, EGRs, general engine problems, EVAP and Emissions issues.

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