A replacement requires a Toyota part costing £150 but is easy to fit without taking out the floor pan.
An alternative is to fit an electric substitute, but this must be big enough and reliable. The viscous-coupled fan drains some power from the engine at normal temperatures, even more when it is activated. An electric substitute will conserve some of this.
Dave Mason, editor, Sep 2002
Viscous-coupled fan mounting (top and lower left) and water pump (centre and lower right) . Note that these are quite separate components. The water pump is driven off the back of the cambelt.
David Miller (Oct 03) came up with this interesting morsel taken from the Mazda RF diesel section of the Grand Vitara's manual. It explains rather nicely the workings of the viscous coupling - which David says is identical to the one in Townaces ...
"COOLING FAN CLUTCH - Fluid is enclosed in the cooling fan clutch and at its center front, there is a bimetal whose thermal reaction and the engine speed control the cooling fan speed. The relation between the temperature detected by the fan clutch and operation of the fan clutch is as follows.
David adds ...
Obviously the temperatures and rpms may differ slightly on the Townace, but it does paint a nice picture of the control afforded by the coupling; engine torque and speed vs. fan loading = fan speed. Obviously one must bear in mind that the fan rpms are maximums and cannot exceed crank speed by more than pulley ratios.
In the cause of Ace Answers, John Davis DID disassemble his (old) fan clutch (Apr 2003) and reported ...
This view is of the outer half of the Aisin viscous coupling, as fitted to the Townace range. On the fan side of this half of the coupling (underneath in this view) is the temperature sensitive, bi-metallic spring, which opens and closes a reed type valve, allowing viscous fluid to pass from the reservoir, into the "driving" chamber of the coupling. Part of the reed valve can be seen in the centre of the coupling, and it is turned by the central spindle, which is connected to the bi-metallic spring. The "ports" can be seen at 5.00 o'clock and 11 o'clock. The inner pair of ports are opened when the air temperature, over the radiator, causes the bi-metallic spring to turn the central spindle through a small arc (approx 3 or 4 degrees). The reed valve uncovers the inner ports and viscous fluid flows into the "drive" chamber. At the same time, the two outer ports are closed.
The viscous fluid is flung outwards, by centrifugal force, to the outside edge of the couping body, where it is trapped between the outer bore of the coupling and the bevelled gear type "drive" teeth on the outside of the driven rotor. This "interference" drive drags the rotor, which is connected directly to the fan, up to somewhere near engine speed when the heated air, passing over the radiator, has opened the valve fully enough to fill the "drive" chamber with fluid. At the 6.00 o'clock position, you will see a small, drilled, port, just behind a "step" in the outer bore of the chamber. This, I think, is the "scoop" valve, which forces the viscous fluid, back into the reservoir chamber, when the radiator temperature has fallen low enough to allow the bi-metallic spring/valve assembly to close the two inner ports and open the two outer "return" ports. The two cross headed screws are to allow fine adjustment of the position of the valve relative to the two ports.
Another view of the rotor showing three milled apertures which, I think, are there to assist the fluid to pass to the small clearance between the rotor (fixed to the fan) and the coupling body, being driven by the fan belt.
On the two faces of the coupling halves is a square section groove, which takes a neoprene sealing ring. This is trapped between the two halves when they are bolted together and the groove can be seen just inside the mounting stud locations.
On test, with the bi-metallic spring/valve assembly heated via a hair dryer, the two reservoir ports, i.e. the ports allowing fluid to pass into the "drive" chamber, hardly opened. It took the temperature of an oven hotplate to get the valve to fully uncover the ports and, in my view, with an old coupling, the coolant temperature would get to a much too high figure before the fan started to "drive"and there would be great benefit in altering the position of the valve to allow these ports to be opened at a lower temperature. This can easily be done by adjusting the valve via the two cross head screws.