There are always various problems in a car engine. The “yes-yes-yes” engine sound on cold start is something that everyone often encounters, and car owners also consider it most annoying problem. Most car owners are more careful with their car, especially when car is cold starting, many car owners have a habit of warming up car, so why does engine make a “yes yes” sound when starting a cold car? Is this noise normal?
In fact, when engine is started cold, due to oil's thickness and poor fluidity, running noise may occur after a short period of time, as well as a slight noise when moving parts come into contact with each other. normal and no need to worry.
Cold starting a vehicle means that vehicle has been parked for a long time and engine starts when vehicle temperature is equal to ambient temperature. Many car owners hear a “yes-yes” sound from engine compartment when car is cold started, this sound is very abnormal, unlike car in normal operation. This is very puzzling for many car owners, and even for some new cars this situation occurs already during break-in period: sound of starting engine is loud.
What causes engine to make a rattling sound when starting a cold car?
Typically, main sources of abnormal cold start noise are poor engine valve seals and poor lubrication, a belt that is too tight, or abnormal bearing noise. If abnormal sound persists after engine temperature rises, owner needs to go to a service station for a more detailed inspection.
The belt is too tight and there is an "abnormal sound" when starting a cold car. Reason 1
When car is parked during day, engine lubricating oil mostly drains back into oil pan. When engine is cold-started, oil pump cannot immediately establish oil pressure, and an oil film forms between them. components, especially cylinder head (upper part) Internal valves are not lubricated at cold start, whether it is hydraulic tappet or mechanical rocker, there will be a certain valve clearance, resulting in rattling sounds.
When engine is running for a while, oil pressure rises and an oil film forms, engine oil temperature rises, and “yes-yes” sound disappears after engine runs normally.
(Attention, if engine continues to rumble on a hot car, take it to a repair shop for inspection as soon as possible)
Cause 2 of "anomalous noise" when starting a cold car
Besides engine oil, there is another engine component that will also make a rattling sound, charcoal filter solenoid valve (purge valve), which is installed in charcoal filter and intake manifold when engine is started. The solenoid valve between them opens, and gasoline vapors absorbed by carbon filter are brought into cylinder by air under vacuum of intake manifold to participate in combustion.
This not only reduces emissions, but also reduces fuel consumption, and rattling sounds will be heard during operation.
(Addendum: Oil quality problems can sometimes cause engine to rattle.) Therefore, a rattling sound when vehicle is cold-started is not a malfunction. If this abnormal sound occurs when car is hot, you need to pay attention. This phenomenon also occurs when starting.
Summary
When starting engine, a rattling sound will be heard, which disappears after car has warmed up or been driven for a certain period of time. This is normal and owner does not need to worry about it.
In general, when starting a cold car, engine sound will be slightly louder than when starting a hot car, as long as sound is smooth and soft, not harsh. This is due to fact that on a cold car, gap between cylinder wall and piston has not reached optimal size, and engine oil lubrication is not enough. Usually, when engine block temperature reaches 95 degrees, sound returns to normal.