···
Log in / Register

Why does the car make a rattling sound at idle when hot but not when cold?

4 Answers
MacIsabella
07/24/25 11:52pm
Here are the reasons for the "abnormal noise" during cold starts: 1. Oil pump: After the car has been parked for a day, the engine's lubricating oil has mostly flowed back into the oil pan. During a cold start, the oil pump cannot immediately establish oil pressure, and oil films cannot form between components, especially the valves in the cylinder head (upper part). Whether it's hydraulic lifters or mechanical rocker arms, there will be some valve clearance, resulting in a rattling sound. 2. Charcoal canister solenoid valve: Besides the oil issue, another component that can cause a rattling sound is the charcoal canister solenoid valve (purge valve). Its function is to open the solenoid valve between the charcoal canister and the intake manifold after the engine starts, allowing the gasoline vapor adsorbed by the charcoal canister to be drawn into the cylinders by the vacuum in the intake manifold to participate in combustion.
Was this review help?
19
5
Share
BraxtonDella
08/10/25 10:43am
The other day my car made a ticking noise at idle when warmed up, but was completely silent when cold, which really puzzled me. When the engine heats up, components expand, possibly increasing valve clearance or causing insufficient oil supply to hydraulic lifters, leading to metallic knocking sounds. It's like how people tend to stretch more in hot weather—thermal expansion increases friction. When cold, the oil is more viscous and lubricates better, so the noise is minimal. I recommend first checking if the oil level is adequate and whether the oil is clean; dirty oil has poor flow properties, and when hot, dropping oil pressure can cause noise. Sticking piston rings can also cause this, common in older cars. Don't drive recklessly when you hear such noises—safety first. Take it to a repair shop to have them use a stethoscope on the valve area; don't try to save money by guessing and risk bigger problems. Regular oil changes and maintenance can prevent this issue.
Was this review help?
5
4
Share
Expand All
CarsonMarie
09/26/25 7:25am
As a female driver, I was terrified when I encountered the situation where the engine made a ticking noise when hot but was silent when cold. Later, after learning some mechanical knowledge, I understood: when the engine heats up, metal expands, increasing the gaps, and if lubrication can't keep up, the valve system or pistons start knocking. It's like the sizzling sound of stir-frying in a hot pan—quiet when cold. The most common issue is with the engine oil—low viscosity or insufficient quantity causes oil pressure to drop, and the oil pump can't maintain adequate pressure. Try switching to a better quality oil and avoid using inferior products. Also, check if the timing chain is loose; in older cars, wear can cause the chain to make noise when hot. This is a significant hazard, especially if the noise suddenly appears while driving at high speeds—get the chassis and lubrication system checked on a lift as soon as possible. Don’t slack on daily maintenance; choose the right oil brand to prevent degradation and easily extend your engine’s lifespan.
Was this review help?
18
4
Share
Expand All
MacAaliyah
11/10/25 2:41am
With decades of car repair experience, I've seen it all: Ticking sounds when the engine is hot but silence when cold are caused by thermal expansion and lubrication failures. Internal components like valve lifters expand with heat and contract when cold—when the gap widens and oil pressure can't keep up, they rattle. Low oil viscosity or a weak oil pump can also cause this. Stuck piston rings create friction noises when they expand under high temperatures. This sound is common in older cars, but even new vehicles can develop it due to poor maintenance. Check oil level and quality—top up if low, replace if dirty. Avoid immediate starts; warm up the engine before driving to reduce thermal shock. Poor lubrication can destroy an engine—early intervention saves money.
Was this review help?
17
2
Share
Expand All
More Forum Discussions

Should I Continue Practicing Driving After Failing Subject Two?

Subject Two is inherently challenging, placing certain demands on both driving skills and mindset. Regardless of the reason for failing, it is still necessary to continue practicing. Below is relevant information: Subject Two: Also known as the small road test, Subject Two is part of the motor vehicle driver's license examination, specifically the field driving skills test. For the C1 license, the test includes five mandatory items: reverse parking, parallel parking, stopping and starting on a slope, right-angle turns, and curve driving (commonly known as S-curves). Some regions may include a sixth item, such as high-speed toll collection. For the C2 license, the test includes four mandatory items: reverse parking, parallel parking, right-angle turns, and curve driving (commonly known as S-curves). Teaching Objectives: Master the basic essentials of driving operations and possess fundamental vehicle control abilities; proficiently grasp the basic methods of field and road driving, with the ability to reasonably use vehicle controls and correctly manage the vehicle's spatial position, accurately controlling the vehicle's position, speed, and route.
3
0
Share

Where is the charging port of a tricycle?

Electric tricycles generally have their charging ports located around the seat box or on the left or right side of the front lower part of the cargo bed. Below is relevant information: Additional Information: Electric tricycles typically use lead-acid batteries, with a charging time generally between 8 to 10 hours, and should not exceed 12 hours. It is recommended to charge for a limited time to better preserve battery life, as overcharging can cause severe water loss and negatively impact battery longevity. The optimal time to recharge the battery is when the remaining capacity is between 30% to 40%. Tricycle: A tricycle is a vehicle modified from a bicycle, capable of carrying passengers or goods. It became very popular after the 1930s and gradually replaced the role of rickshaws. Tricycles are a combination of rickshaws and bicycles. They can be categorized into human-powered tricycles, electric tricycles, children's tricycles, and battery-powered tricycles, among others.
14
4
Share

What Causes Delayed Ignition After a Car is Exposed to Sunlight?

Difficulty starting a car after prolonged exposure to sunlight is often due to a faulty carbon canister solenoid valve. If the carbon canister solenoid valve remains open, fuel vapors can enter the intake manifold through the carbon canister after sun exposure, causing an overly rich air-fuel mixture during engine startup, which leads to difficulty in starting the car. Here are some relevant solutions: Turn off the engine: If the ignition difficulty is caused by a faulty carbon canister solenoid valve, the solution is to turn off the engine, disconnect the connecting pipe, and attempt to suck air through it. A properly functioning carbon canister solenoid valve should not allow air to pass when closed. If air can be sucked through, it indicates damage and requires replacement. Cool down: If the external temperature is excessively high, it may affect the coolant temperature sensor, triggering the vehicle's protection program to prevent damage. This may keep the vehicle in a shutdown state until the external temperature returns to normal, allowing the car to start properly.
6
3
Share

What lights should be used when driving at night under poor lighting conditions without street lights?

When driving at night without street lights and under poor lighting conditions, high beams should be turned on. Here is some relevant information: Car lights: Car lights refer to the lamps on the vehicle, which are tools for road illumination during nighttime driving and also serve as signaling devices for various vehicle movements. Car lights are generally divided into headlights, taillights, turn signals, etc. Halogen headlights: Halogen lamps are actually a special type of incandescent lamp. Their principle is that when current passes through a resistor, it generates heat, and when the temperature is high enough, it emits blackbody radiation with wavelengths in the visible light spectrum. There are generally two types of halogen lamps: iodine tungsten lamps and bromine tungsten lamps, which operate on the same principle. When an incandescent lamp is lit, although the filament temperature does not exceed the melting and boiling points of tungsten, a small amount of tungsten still volatilizes at high temperatures. When the volatilized tungsten atoms encounter the cooler bulb shell, they condense and precipitate. Over time, a layer of blackened tungsten film accumulates on the bulb shell.
18
1
Share

What Are the Black Stains That Can't Be Wiped Off a White Car?

Black stains on white cars are mainly caused by calcium oxide carried in rainwater that settles on the vehicle, which can also appear on glass. If they cannot be removed with cleaning agents, polishing may be considered. Here is some related information: Car Window Tinting: Car window tinting (Auto-tint-film) involves applying a thin film to the front and rear windshields, side windows, and sunroof of a vehicle. This film is also known as solar film or heat-insulating film. Vehicle Body Maintenance: Vehicle body maintenance is commonly referred to as car detailing. Its primary purpose is to remove various forms of oxidation, corrosion, and contaminants from both the exterior and interior of the vehicle, followed by protective measures to enhance the vehicle's 'beauty'. It mainly includes: paint maintenance, interior maintenance, chrome plating maintenance, leather and plastic maintenance, tire and wheel hub maintenance, windshield maintenance, chassis maintenance, and engine exterior maintenance, among others.
4
1
Share

What are the reasons why a self-balancing scooter won't turn on?

Self-balancing scooter won't turn on may be due to abnormal power-on circuit or abnormal power supply circuit of the battery. Here is relevant information: Electric self-balancing scooter: Also called hoverboard, segway, or electric unicycle. There are mainly two types on the market: single-wheel and dual-wheel. Its operation principle is mainly based on a basic principle called "dynamic stability". Features of self-balancing scooters: Environmentally friendly. Powered by rechargeable batteries, they cause no pollution to the environment, are absolutely eco-friendly, and can be recharged repeatedly. Moreover, the electric motor operates with high efficiency and low noise, thus reducing noise pollution and saving energy.
14
5
Share
Cookie
Cookie Settings
© 2025 Servanan International Pte. Ltd.