viscous fan

[CarloL]

Hi

Quick one , I have a Toyota Supra with a viscous fan (OE) , the loom is 24 years old and heater control unit failed on me ; I have sourced 2nd hand 3-4 units (it is discontinued) but all had their own defects

In terms of running a PDM and new loom with a keypad ; I presume only electric fans are compatible as opposed the OE viscous fan; I would like to retain the viscous fan as it is more efficient and cost effective

Can you run the viscous fan via a PDM & keypad ? or what are my options

[SportsCarRacer]

Hi Carlol.

Viscous fans (especially Toyota!) Are mostly mechanically actuated via a bimetallic "valve" on the fan...no wlectrical connection controls the oil flow...
However some vehicles use(d) an electrical PWM solenoid that pushes on the "valve lever" than controls the flow of the viscous fluid between the working chamber and the internal resevoir. Most of the elec solenoid ones i've experienced (eg Mahle style) also have a speed sensor to feedback to the PCM the fan speed for the pcm to control (via closed loop PWM control of the valve lever solenoid)...typically dc=1 is fully disengaged and dc 0.9~0.5 is varios levels of fan slip...limited of course by centrifugal effects on the oil based on enginw (fan pulley) speed.
This latter type is common on North American products.....but most (not all!) JDM stuff i have seen (even 2018my stuff) has the more conventional bimetallic control of the fan (no wires!)
The former can be controlled by 1A output of any m1 (eg hb) that can do duty cycles 0-100%, but be aware some have pwm freq as low as 2hz, although 5-10hz is more common.
If its bimetallic pcm cant touch it!!!
Ps some modern OEM electric fans can move incredible amounts of air..and draw incredible currents too..one mainstream OEM elec fanis 1040w (most light commercials are only 800w max), pulling just over 80A...it was designed to replace sn electrically controlled Mahle viscous fan....more aur with much better control on demand (ie low eng spd)..as long as you can tolerate the current draw.
Viscous is old, relatively undurable at high time in service, compared to elec fans...

My 20c worth after 20 years of OEM experience with them

[CarloL]

Thank you , great response!

[Sydney Anders]

I've had this issue too!
Thanks for the response.