[star_aqua]

Originally Posted by MileCruncher

So what you mean to say that there will be instances when the fan shouldn't be moving right. But I have never seen that happen i.e. the fan actually not rotating while the engine is on.

Could you please explain further.

to add more, just observe the fan while switching off the engine. the fan stops later after the engine is shutdown.
The viscous coupled clutch along with the thermostat can maintain the engine temperature at constant value through out the engine operation with various loads and conditions.
where as the electric fans are hysteresis type if not calibrated well, keeps the engine temperature varying between a specified range.

[headers]

Originally Posted by SPIKE ARRESTOR

The fan for the Radiator in a Bolero is of Viscous clutch type.

WOW - thats nice..

Originally Posted by SPIKE ARRESTOR

b) The viscous fan is engaged only under 5-15% of normal operating conditions, otherwise the radiator is cooled through Ram air cooling, this is done to reduce the parasitic losses resulting due to parts coupled to the power plant. The viscous fan engages and disengages in accordance with the bimetallic coil placed inside the assembly. This happens when a pre-set temperature is reached.

Spike

BTW, what is THAT preset temperature Spike??

Originally Posted by MileCruncher

So what you mean to say that there will be instances when the fan shouldn't be moving right. But I have never seen that happen i.e. the fan actually not rotating while the engine is on.

You can see the fan not moving if you are travelling at 100kph and have a peek at the fan from the front

Originally Posted by SPIKE ARRESTOR

@MC, have you seen it when the Ram air is actually in full swing ? No, you must have seen it while in Kerb idle, in most conditions the fan is just freewheeling and not actually engaged. During freewheel the fan rotates but only at ~ 800 RPM, it is only when the engine is loaded the fan engages. This is felt when:-
1. The engine sound increases to a slight roar
2. Fan spins faster ~ 1800 RPM and above.

Spike

Yes you can easily hear the fan roaring above the diesel clatter..

Originally Posted by star_aqua

to add more, just observe the fan while switching off the engine. the fan stops later after the engine is shutdown.
The viscous coupled clutch along with the thermostat can maintain the engine temperature at constant value through out the engine operation with various loads and conditions.
where as the electric fans are hysteresis type if not calibrated well, keeps the engine temperature varying between a specified range.

super explanation sir. you are a true engineer.

[ex670c]

Originally Posted by SPIKE ARRESTOR

b) The viscous fan is engaged only under 5-15% of normal operating conditions, otherwise the radiator is cooled through Ram air cooling, this is done to reduce the parasitic losses resulting due to parts coupled to the power plant. The viscous fan engages and disengages in accordance with the bimetallic coil placed inside the assembly. This happens when a pre-set temperature is reached.

Hi Spike,

What about 4WD-Lo Trail Driving or worse conditions, when there is no "Ram Air Cooling"

What will happen if the VC Fan is replaced with a conventional fan?

Regards,

Arka

[Samurai]

Originally Posted by star_aqua

where as the electric fans are hysteresis type if not calibrated well, keeps the engine temperature varying between a specified range.

Oh! Thanks for reminding that word, hadn't heard since college. For a moment I wondered, then the image hit me from the memory lanes.

Originally Posted by headers

You can see the fan not moving if you are travelling at 100kph and have a peek at the fan from the front

I am shocked that you would try something like that, peeking at the fan from the front at 100kmph.

[MileCruncher]

Originally Posted by SPIKE ARRESTOR

@MC, have you seen it when the Ram air is actually in full swing ? No, you must have seen it while in Kerb idle, in most conditions the fan is just freewheeling and not actually engaged. During freewheel the fan rotates but only at ~ 800 RPM, it is only when the engine is loaded the fan engages. This is felt when:-
1. The engine sound increases to a slight roar
2. Fan spins faster ~ 1800 RPM and above.

Spike

But I thought the fan speed was directly proportional to the engine RPM. So If the engine is at 3k RPM will the fan rotate at K X 3K RPM (where K = PUlley factor) or still rotate around 1800 or thereabout RPM

[SPIKE ARRESTOR]

^ Arka, even without "Ram Air cooling" it will work without breaking any sweat. What do you think will happen if it is replaced with a conventional fan?

Spike

[ex670c]

Originally Posted by SPIKE ARRESTOR

^ Arka, even without "Ram Air cooling" it will work without breaking any sweat. What do you think will happen if it is replaced with a conventional fan?

Hi Spike,

If replaced by a Conventional Fan, the vehicle will run cooler.

Regards,

Arka

[SPIKE ARRESTOR]

Originally Posted by MileCruncher

But I thought the fan speed was directly proportional to the engine RPM. So If the engine is at 3k RPM will the fan rotate at K X 3K RPM (where K = PUlley factor) or still rotate around 1800 or thereabout RPM

Yes!

Originally Posted by ex670c

Hi Spike,

If replaced by a Conventional Fan, the vehicle will run cooler.

Regards,

Arka

The system becomes an open loop type without any feedback. What will you gain with this setup?

Spike

[ex670c]

Originally Posted by SPIKE ARRESTOR

The system becomes an open loop type without any feedback. What will you gain with this setup?

Hi Spike,

The gain is the ability to run cooler or cool down faster, especially in very slow and hot situations.

A minor gain will be drag caused by the VC fan.

Regards,

Arka

[Jaggu]

Wont the cooling be too much also sometime especially places like BLR etc ?? ie if its running same speed through out.

[Samurai]

Originally Posted by ex670c

The gain is the ability to run cooler or cool down faster, especially in very slow and hot situations.

Even a close-loop system (with feedback) achieves the same thing. Try turning on AC in a car kept under hot sun for hours.

1) In case of climate controlled AC, the blower will go insane to achieve fast cool-down. The blower will slow down, once the cabin is cool.
2) In case of regular AC, the blower will blow at the same rate, when the car is hot and when it is cooled.

[Jaggu]

But in 2) the AC if it does not have any thermostat wont it chill to kill?

[headers]

Hey guys,

The VC fan is installed to reduce the work on the engine. Most modern vehicles have a electric VC fan to ensure the fan does not work when NOT needed. It will work as a normal fan if the temperature exceeds the preset point.

During High speed crusing, especially in vehicles such as the THAR, great work is established breaking the wind. Some of it is let inside to help cool the engine via the radiator and VC fan.

Not having this VC fan will not have any issue apart from the engine having to move the fan under all circumstances.

@Spike: please elaborate post #113 as to how the system becomes an open loop when the VC fan is replaced by a regular fan!!!

It becomes open loop only if the thermostat is removed IMO.

[MileCruncher]

Originally Posted by headers

@Spike: please elaborate post #113 as to how the system becomes an open loop when the VC fan is replaced by a regular fan!!!

It becomes open loop only if the thermostat is removed IMO.

Technically it shouldn't. All it should do is making the thermostat close faster during the long runs. But removing the thermostat will reduce the thermal efficiency of the engine and is not good at all in cold climes.

[Samurai]

Originally Posted by Jaggu

But in 2) the AC if it does not have any thermostat wont it chill to kill?

Yes, it will, if the human in the car doesn't lean forward and reduce the AC. In non climate control AC, it is the human who closes the loop.