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Thermo Fans

Being a rotary owner, one thing that always is in the back of your mind is "cooling". The factory fitted cooling may be adequate for "normal" driving, and given the Cosmo was only released in Japan, for their climate, the specifications may not meet an acceptable standard for our driving conditions.
As part of a two stage improvement, the mechanical clutch fan and OEM electric fans are going to be replaced with twin electric, thermostatically controlled fans. The benefits are manifold; through reduction of losses when the mechanical fan is operating (which is quite frequent), the clawing back of valuable engine bay space, aesthetic purposes, and access to the (future) Electric Water Pump (EWP) addition.

The OEM mechanical clutch fan is triggered by one condition - heat based expansion of a fluid housed within the fan mechanism.

The OEM electric fan is triggered by three conditions:
1. Temperature
2. Air conditioner operation, and
3. Fail Safe for loss of circuit integrity.

The design of this modification is to have both fans operate from a single thermo switch, but for a Fail Safe state, have each power supply sourced independently. To further meet a much as a fail safe operation, the primary fan can still be operated by the OEM temperature switch (in case of failure of the new thermo switch). This should provide accurate cooling control over radiator coolant temperatures.

Both fans are designed to operate regardless of ignition status; ie it will run with the ignition off.
* While this may mean considerable "run on" after the engine is switched off, this situation will be addressed effectively once an electric water pump is fitted.


The main materials:
2 x 14" fans
1 x Thermo switch

Most of the other materials come with these kits with the exception of a diode that I installed in the control circuit.



The thermostat:



The fans:

  The fans demonstrating the radiator coverage on a standard Cosmo 20B radiator:    

The following steps are required to prepare for the installation of the fans:
1. Remove the undertray
2. Remove the small shroud that covers the gap between the intercooler and radiator
3. Remove the intercooler pipes (the flexible hoses at the top (2) and the alloy pipes to the top of the intercooler)
4. Unbolt the radiator fan shroud - 3 x 10mm bolts along the top and 3 along the bottom (this will also release the OEM thermo fan)
5. Unplug and remove the OEM thermo fan
6. Unbolt the mechanical clutch fan and remove - 4 x 10mm nuts
7. Remove radiator fan shroud
8. Remove top (2) radiator brackets to allow better access to the front of the radiator.




Using the mounting kits supplied with the new fans, mount the fans to the radiator. Note: read manufacturers instructions to ensure fan blades are configured to "pull" air rather than "push".
(There is no point in going into detail of this step as installation will vary dependant on fan manufacturer.)




  The mounting hardware supplied with the fans I purchased do not meet an acceptable standard in my opinion. I ended up using 1/8" screws with nuts, fibre washers, rubber washers and steel washers. I also used high temperature sylastic to work as a locking mechanism, chosen as it can also be physically removed if necessary.



The installation is quite straight forward, and on completion the intercooler pipes, undertray and radiator brackets can be reinstalled.



The wiring of the primary fan is straight forward as it uses the OEM controls.
Cut the plug off the OEM fan with enough cable to extend the wiring from the new fan to the existing plug (I chose the drivers side as the primary for ease of wiring).
Cut the plug off the new fan and solder the OEM plug to the new fan. ** Take care to ensure correct polarity - refer to fan manufacturers instructions to ensure correct configuration regarding "pushing" or "pulling".
Plug this fan in and test by turning on the ignition and disconnecting the thermo switch on the water pipe adjacent the thermostat housing (the black spade lug type).
The fan will now operate as per the OEM thermo fan.




The main control requires the installation of the thermo switch, relay, fuse and wiring.
The best idea is to follow the manufacturers instructions regarding the installation of the switch. Power for the secondary fan can be sourced directly from the battery, through a fuse and relay. Power to the thermo switch can be sourced directly from the battery as well (so they operate regardless of ignition switch position) or from a ignition source.

Both fans should be set up to operate from the thermo switch. The primary fan will still operate from the OEM controls so will provide protection in the case of thermo switch failure. In my case, I installed a diode between the relay previously installed here and the new relay. There are too many options to go into detail or the pros and cons of any particular setup. If you'd like to discuss the best options for your situation, or require any wiring diagrams / advice, I can be contacted here.




** After some testing and adjusting, the thermo fans operate consistently within an acceptable range. This includes:
- generally off while driving
- start after 30 seconds idling (traffic lights, etc)
- Cycles while hot idling: 20 seconds on; 30 seconds off.
This meets / exceeds expectations.
When the fans are running there is a noticeable heat dissipation around the car. Warm air movement can be felt under the vehicle and to each side. The conclusion is that this cooling method is superior to the OEM method. (Note that the JC Cosmo was the last rotary engine produced that used a mechanical clutch fan. Subsequent models utilised thermo fans only.)
There is a noticeable change to engine load (alternator) as the fans activate - this variation is the same or less than the mechanical clutch fan loading.
A notable observation has been that the mechanical clutch fan was engaged for a significant period of time prior to this upgrade, much more than assumed and only obvious after its removal.
Throttle response has increased considerably.
Freed power through reduction of parasitic load can only be guessed at, but the word "substantial" may be apt.