Over Heating

In 1st gear, the engine can reach higher rpm in lesser time. so the temperature exceeds normal operating temperature and also velocity of air flown on the radiator is less due to low speed of the vehicle(ie. convective heat transfer is less).

Nagarajamoorthy

In 1st gear, the engine can reach higher rpm in lesser time. so the temperature exceeds normal operating temperature and also velocity of air flown on the radiator is less due to low speed of the vehicle(ie. convective heat transfer is less).

Am sure that the excessive consumption of fuel when the car is on first gear is as a result of the gear ratio...in the gear box....the engine will turn to it normal rpm...if there is no obstacle but the gear ratio will let the engine breath more..... I hope am right

Safo Kofi

..... I hope am right

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You are not right.

Yes there will be more fuel used than when a more appropriate gearing is used, but the amount of fuel used is not the cause, and neither is the amount of intake air or exhaust volume.
For example, when running at high speed in 'high gear', the amount of fuel, air, and exhaust would be more than when running at high rpm in a low gear - but the engine would not overheat. At high speed there is adequate airflow thru the radiator (and/or around the engine) to remove enough heat so the engine does not overheat. At low speed and high rpm the amount of airflow is NOT ADEQUATE.

Overheating occurs when the cooling system cannot prevent continual heat increase in the engine. The cooling system is designed to be adequate to maintain a stable engine temperature WHEN THE VEHICLE IS USED AS INTENTED. Running at high rpm in low gear violates the usage instructions in the vehicle's USER MANUAL.

Jay Kosta
Endwell NY USA

Jay Kosta

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You are not right.

Yes there will be more fuel used than when a more appropriate gearing is used, but the amount of fuel used is not the cause, and neither is the amount of intake air or exhaust volume.
For example, when running at high speed in 'high gear', the amount of fuel, air, and exhaust would be more than when running at high rpm in a low gear - but the engine would not overheat. At high speed there is adequate airflow thru the radiator (and/or around the engine) to remove enough heat so the engine does not overheat. At low speed and high rpm the amount of airflow is NOT ADEQUATE.

Overheating occurs when the cooling system cannot prevent continual heat increase in the engine. The cooling system is designed to be adequate to maintain a stable engine temperature WHEN THE VEHICLE IS USED AS INTENTED. Running at high rpm in low gear violates the usage instructions in the vehicle's USER MANUAL.

Jay Kosta
Endwell NY USA

Does is it mean that airflow through the radiator varies with respect to gear

Safo Kofi

Does is it mean that airflow through the radiator varies with respect to gear

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Only to a minor amount.

Typically there is a fan mounted near the back of the radiator. On some older engines the fan was driven by a belt (the fan belt) directly from the crankshaft. In some cases there is a temperature sensity mechanical clutch that engages the fan blades only above a certain temperature.
On other engines the fan is powered by its own electric motor, and the fan only receives power if the engine is above a certain temperature.

Such a fan is most helpful for drawing air through the radiator when the vehicle is stopped, or moving slowly - such as in heavy stop-and-go traffic. But the fan would not be able to draw enough air for adequate cooling if the engine rpm is overly high and the vehicle is moving slowly.
When the vehicle is moving faster than about 20 kph, I think the airflow through the front grill is enough to cool the radiator.

Some 'special purpose' vehicles have heavy-duty radiators and fans that can provide adequate cooling at slow speed.. For example taxicabs, and police cars that often spend a lot of time moving slowly, or idling while stopped with air conditioner running.

I don't know of any vehicle application where the gear ratio or engine rpm is directly monitored to control the air flow. The gear and rpm would affect the engine temperature, and the engine temperature IS monitored and controls the cooling system.

The cooling system uses engine power, so it can reduce the amount of power that reaches the wheels. For best efficiency, the cooling system should only actively use power to prevent the engine from getting too hot. And the components of the cooling system shoud not be overly heavy.

Jay Kosta
Endwell NY USA

In Detail for better understanding
Engine is an Internal Combustion Engine. Diesel or petrol along with air is the FUEL for combustion. when the fuel ignite, explosion happens in an IC engine. which is a controlled Explosion. the explosion produce 1.Pressure forces which in turn create mechanical motion and 2.heat (around 1800 to 2500 c ). mechanical motion is the work done by pressure force
(chemical energy $$fuel &air$$ is converted into 1) mechanical and 2)heat or thermal energy) pressure forces released on explosion moves the piston and rotates the CAM shaft. only around 80 to 100 C is required for functioning and remaining heat produced is flushed out of the system by cooling system.
cooling of engine or excess heat flushing of engine is done by coolant liquid and air blown on engine and exhaust gas.
In IDLING or in neutral gear, petrol engine runs at 800 rpm. in 1st gear the engine moves the load with minimum effort as the power of the engine is used to produce more turning force or torque by GEAR BOX. on revving the engine RPM increase but speed of vehicle is between 0 to 20 in 1st gear.
coming back to cooling system
1.coolant liquid is pumped in * cool and pumped out
(hot )of the engine is by coolant pump operated by engine power
2. air blown or forced in to the bonnet cools the radiator and engine by taking away heat through conductive and convective heat transfer.
the rate of heat carried away is depending on the atmospheric temperature of air. and speed at which air is blown.
POINT IS at low speed of vehicle the speed of air at which it is blown in to bonnet is less and even zero in idling. at this point the electric fan comes to rescue the engine from over heating but the heat carrying capacity of air blown by fan is sometimes less
due to saturation of heat in air due to high temperature or heat or high latent heat.
so THE ENGINE OVER HEATS and damages the parts of engine due to high heat and even ceases motion of piston due to expansion

Nagarajamoorthy

...
pressure forces released on explosion moves the piston and rotates the CAM shaft.
...

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Very minor correction made to help avoid confusion about IC engine operation.

The piston is connected to the rotating CRANKSHAFT by a 'connecting rod', and the crankshaft connects to the transmission as the pathway for powering the wheels.

The CAM shaft is made to rotate by either gears, a belt or chain from the crankshaft.
The function of the cam shaft is to power the opening and closing of the intake and exhaust valves at the proper time, and is synchronized with the position of the .
pistons.

Jay Kosta
Endwell NY USA

Thank you kosta, for correction
In Detail for better understanding
Engine is an Internal Combustion Engine. Diesel or petrol along with air is the FUEL for combustion. when the fuel ignite, explosion happens in an IC engine. which is a controlled Explosion. the explosion produce 1.Pressure forces which in turn create mechanical motion and 2.heat (around 1800 to 2500 c ). mechanical motion is the work done by pressure force
(chemical energy $$fuel &air$$ is converted into 1) mechanical and 2)heat or thermal energy) pressure forces released on explosion moves the piston and rotates the CRANK shaft, there by producing rotational motion.which is then transferred to wheels through gear box . only around 80 to 100 C is required for functioning and remaining heat produced is flushed out of the system by cooling system.
cooling of engine or excess heat flushing of engine is done by coolant liquid and air blown on engine and exhaust gas.
In IDLING or in neutral gear, petrol engine runs at 800 rpm. in 1st gear the engine moves the load with minimum effort as the power of the engine is used to produce more turning force or torque by GEAR BOX. on revving the engine RPM increase but speed of vehicle is between 0 to 20 in 1st gear.
coming back to cooling system
1.coolant liquid is pumped in * cool and pumped out
(hot )of the engine is by coolant pump operated by engine power
2. air blown or forced in to the bonnet cools the radiator and engine by taking away heat through conductive and convective heat transfer.
the rate of heat carried away is depending on the atmospheric temperature of air. and speed at which air is blown.
POINT IS at low speed of vehicle the speed of air at which it is blown in to bonnet is less and even zero in idling. at this point the electric fan comes to rescue the engine from over heating but the heat carrying capacity of air blown by fan is sometimes less
due to saturation of heat in air due to high temperature or heat or high latent heat.
so THE ENGINE OVER HEATS and damages the parts of engine due to high heat and even ceases motion of piston due to expansion