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Which Forces Keep Car Running Or Fan Circulating After Switch Off


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#1 newrobert

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Posted 17 November 2014 - 12:16 PM

Hi guy,

 

Please help me to understand that which forces help car still running even after switching off ignition or fan keep circulating even switching off button.

 

Thank you

 

Robert

 



#2 BrettNortje

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Posted 19 January 2015 - 09:46 AM

Hi guy,

 

Please help me to understand that which forces help car still running even after switching off ignition or fan keep circulating even switching off button.

 

Thank you

 

Robert

 

It is most probably momentum or the battery not being put off fully.



#3 SwoopdeSwoop

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Posted 29 January 2015 - 05:20 PM

It heavily depends on the car.

 

When you turn the ignition all you are doing is cutting electrical power to the spark plugs and fuel injectors/pump. Until that power turns off, your engine is still spinning around ~10 times a second. That's several pounds of metal flying around at 10 times a second. It won't just stop instantly. Frictional forces along the drivetrain and internally within the engine take some time to work to stop the motor. The flywheel assembly (assuming it is a manual transmission) also maintains momentum of the drivetrain.

 

The fan keeps circulating as a part of a safety feature in some cars. If you just shut your engine off immediately after driving it very hard, it remains extremely hot. But the fluid stops circulating since you've stopped your engine. This is extremely bad for the oil, coolant, and metal surfaces that undergo heavy friction. So to keep your car from cooking in its own juices, some manufacturers have included a feature that detects coolant temperature and keeps the fan and coolant circulating to help cool the engine down quickly after shutdown.

 

Note that this feature does not continue to circulate oil within the engine and may still ruin some of the oil and metal within hot-spots of the engine. This is why high-performance turbocharged engines include things like turbo-timers which keep the engine running after turning the key for a short while. This will allow the engine and turbocharger to cool down before stopping completely.

 

I hope this helps!


Edited by SwoopdeSwoop, 29 January 2015 - 05:21 PM.


#4 Ludwik

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Posted 30 August 2015 - 12:03 PM

Hi guy,

 

Please help me to understand that which forces help car still running even after switching off ignition or fan keep circulating even switching off button.

 

Thank you

 

Robert

What do you mean by "keep running"?



#5 Turtle

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Posted 30 August 2015 - 12:42 PM

... 
When you turn the ignition all you are doing is cutting electrical power to the spark plugs and fuel injectors/pump. Until that power turns off, your engine is still spinning around ~10 times a second. That's several pounds of metal flying around at 10 times a second. It won't just stop instantly. Frictional forces along the drivetrain and internally within the engine take some time to work to stop the motor. The flywheel assembly (assuming it is a manual transmission) also maintains momentum of the drivetrain.

The flywheel is on the engine, not the transmission, and cars with automatic transmissions have a flywheel just as do manual. The flywheel smoothes the jerky action of the pistons and provides the momentum for pistons to get over the top and bottom dead-center positions. Otherwise you are right; the engine can spin for a few seconds after turning off the ignition.
 

The fan keeps circulating as a part of a safety feature in some cars. ...

Correct. To clarify, this is true of newer cars that use electric cooling fans. In older cars the cooling fan is driven by the engine and when the engine stops, the fan stops.

#6 EngineerJosh

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Posted 15 January 2016 - 09:58 AM

To clarify, this is true of newer cars that use electric cooling fans. In older cars the cooling fan is driven by the engine and when the engine stops, the fan stops.

Yeah agreed - newer cars have a lot of stuff like lights, cooling fan etc powered from the 12V battery, older cars are mechanically driven like the fan. 

 

Turtle is spot on. :good:



#7 EngineerJosh

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Posted 15 January 2016 - 10:00 AM

Hi guy,

 

Please help me to understand that which forces help car still running even after switching off ignition or fan keep circulating even switching off button.

 

Thank you

 

Robert

Are you wanting to stop this Robert?  If so you will need to take the battery terminal clamps off the battery which will stop an electrical supply to the car.