Engine cooling fan always runs

[Matt1986]

Hi all. Is it normal for the belt driven fan to always run? Even from a cold start? 

Thanks. Matt

[ste42]

from memory mine always came on at start up

[Tinonline]

Yes they do although regulated by a spring thermo device, its a mechanical fan clutch.

[steve2006]

Mine is hydraulic drive with its own fluid reservoir, not sure how it works as there are also rubber pipes to the engine too.

[Matt1986]

OK thanks guys. Good to know that's normal 

[ambermarine]

Hi Steve

Your Celsior and the Soarers were the only engines fitted with hydraulic fans on the V8 ls400 engines they work through a pump within the fan hub that creates pressure using the fluid from the power steering reservoir ,this pressure engages a clutch that is activated via a thermo switch.

The Lexus LS400 is fitted with a standard mechanical expansion type clutch that engages or releases as the temperature of the engine rises or falls.

The fan runs on engine start up because there is no resistance to the blades the clutch is designed to operate if the car is stationary as the car makes forward motion the airflow coming through the radiator stalls the fan because until the engine temperature reaches  its ideal economical level extra cooling of the rad is not required .If the engine starts to overheat the clutch on the fan expands the fan starts to operate and creates more airflow through the rad.