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http://www.toyotasurf.asn.au/forum/viewtopic.php?p=121443

I was reading somewhere on this forum about changing WHEN the fan engages. It said to rotate it towards the direction where it wants to fight back. I moved it a TINY bit. The black lines are where it was originally.

You have added pre-load to the strip by moving it in the direction you did, the ports will now open at a higher temperature.

Now for the position of the bimetal.

Turn the position against the spring = engage fan later = hotter

Turn away from the spring = engage earlier = cooler

The petrol dissolves the fluid. Just take out as much of the fluid as you can, then wash the rest out with the petrol and a brush.

http://www.toyotasurf.asn.au/forum/viewtopic.php?t=12042&highlight=viscous+fan

he light finally came on after I spent some time looking at it. The strip of metal is a ROTATING VALVE. It controls a couple of orifices that change the fluid available to flow across the ribs in the plates.

Here is my best understanding of how this thing works. On the plate mounted to the water pump there is a series of vanes on the outside of the plate. These vanes try to pull the fluid from the area between the plates. The flow is from the inside of the plates to the outside.

When the clutch is cool, the orifices controlled by the rotating valve are closed. The fluid in the clutch has settled to the bottom of the clutch and some of it is between the ribs – this bit of fluid between the ribs is what causes the clutch to spin when it first starts up. Because of centrifugal force and the above mentioned vanes, it is quickly pumped out and the clutch can spin freely.

As the bi-metal strip heats, it begins to turn the rotating valve. The valve first opens an orifice that is located inside the area of the ribs of the outer plate. On this clutch, that orifice began to open (using the settings it came with) at 50C. That first orifice was fully open at 62C.

The opening of this valve allows fresh fluid to enter the rib section of the plates. The port is closed initially to allow the fluid which has settled overnight in the outer chamber to be pumped out via the two tiny holes on the outside of the chamber.

The bi-metal strip continues to expand with heat and at 70C it begins to open a bigger inverted ‘L’ shaped port that is located on the inside of the plates. This 'L' port is the port that controls the operation of the clutch. When it opens it provides fluid to the outer chamber. The fluid can then flow through the now open first port and into the ribs.

This ‘L’ shaped orifice starts out with the small leg of the ‘L’, then opens up to an even larger area. The second part of the opening to the larger area of flow occurs at 72C. The orifice is fully open by 93C. I suspect that the factory has provided a large enough port that the fully open temperature of 93C is excessive. That is, at some point the port will open far enough that no more opening will provide anymore flow.

It is possible to change the port opening times, however it is not possible to change the maximum resistance. The only way to increase the maximum resistance is by changing the fluid to a thicker fluid.

This clutch is designed so that it will always slip. The fresh fluid flow across the ribs can only be moved by the vanes of the inner plate when there is a difference of speed between the inner and outer plate, that is, when the plates are slipping.

Based upon what I have found, I am going to renew the fluid in the clutch. I am also going to make up the external mechanical ‘lock-out’ mod for use during hill climbs and other sever usage.

Using Matt’s idea of a couple of bolts through the back plate is an easy way to always have the clutch locked-out. Others have simply filled the clutch with epoxy. Either way, these two methods insure that the fan always turns with the water pump pulley. However, I want to be able to easily switch back and forth. I’ll let you know how the mods turn out.

It will be a little while before I complete the lock-out mod. In the mean time anybody with overheating problems could try this quick fix.

Take the fan off the clutch, open the clutch, loosen the two adjusting screws, let the pre-load on the bi-metal spring shift the adjusting plate to the end of the slot, tighten the adjusting screws, bolt the clutch back together, attach fan and bolt the assembly back on the engine.

This will allow the viscous clutch to 'come on' earlier with less heat.

Not a total fix, but it might help. I'm going to do it to my vehicle. Better too early, than a bit too late.

here are three separate chambers; the inner, middle and outer chambers. The inner chamber is closest to the engine and it contains the 50ml reservoir of fluid. The middle chamber has the ‘L’ shaped control port and the outer chamber feeds the port to the clutch ribs. There are also two small holes on the outer edge of the plates that vent the outer reservoir when the clutch is cold.

Here is how I believe the clutch will work under different conditions.

When it is cold, on first starting up, the clutch will run the fan for a short period, perhaps a minute as it drains away the last bit of fluid in the ribs. The fan will then spin freely as there is no fluid in the rib section. This will be the normal condition while the engine is running in cool operating conditions. As the temperature rises, the ‘L’ shaped port begins to open and a small trickle of fluid enters the outer chamber. This trickle will enter the ribs through the rib port and provide some resistance to spin the fan at a faster rate. As the temperature rises further, the remainder of the ‘L’ port is exposed and maximum flow is allowed to the ribs.

If there is inadequate fluid in the clutch, the fan will again first engage at start-up. After about the first minute the fan will no longer have significant resistance to spin – no matter how hot it gets.

If there is too much fluid in the clutch, the fan will first engage at start up, drop back for about 5 minutes while the engine is warming up, then fully engage at operating temperatures and remain engaged.

If the internal adjustment to the bi-metal strip is set too low, it will again engage at start up, drop back for a bit, then the fan will engage early, perhaps even running all the time. If it is set too high, then the fan will only engage at the hottest temperatures.

Using a thicker fluid in the clutch appears to be a good idea. The thicker the fluid, the more resistance the clutch can have when the port opens. The internal adjustment to the bi-metal strip is what determines when the fluid from the inner chamber can begin flowing to the outer chamber.

Using the proper amount of fluid in the clutch is essential to its operation.

That's all I've got at this point, but I feel comfortable with that explanation. I'll let everyone know what the 10000Cwt fluid does. I'm going to pick some up next week.

also interesting to note the fact silicon oils ability to maintain stable viscosity over wide temperature range, quote......

"can be used from -40°C to +280°C

mechanical properties.....

the very high viscosity index, the thermal and chemical stability, shear breakdown resistance and the rubber compatibility as well as the compressibility make this fluid outstanding for mechanical and hydraulic uses."

this oil maintains its viscosity over a wide temperature range and while its viscosity may change slightly does not 'thin' any noticeable amount like 'normal' oils do that one is used to dealing with.

To adjust the pre-load on the bi-metal strip, here's what I did.

Once you get the clutch apart, MARK THE EXISTING POSITION OF THE ADJUSTMENT PLATE. If you loosen the adjustment screws the pre-load on the bi-metal strip will shift the position - remember the pre-load is pushing against the plate's position, so mark it first.

After you get the existing position marked, take the whole unit apart and clean it out. The fluid can be completely cleaned out using petrol.

Now that it is clean, put the adjustment plate back on and set it back where the initial adjustment marks are.

Get a big pot that the adjustment plate will sit down into the heated water. My pot was just the right size that the bi-metal strip was submerged, but the bi-metal strip was not touching the bottom of the pot (the bottom is where you heat the water, plus there is the issue of friction of the bi-metal strip rubbing against the bottom as it tries to expand/contract).

Get enough water in the pot to cover the bi-metal strip. Use a big enough thermometer that you can monitor the temperature.

Heat up the water - THERE IS A LAG IN THE MOVEMENT OF THE ROTATING VALVE AS THE WATER HEATS. Note the 'L' port start to open, when it is fully open, turn off the heat. Now with occasional stirring and monitoring of the thermometer SEE WHEN THE 'L' PORT CLOSES.

By using the temperature of the CLOSING of the port you can avoid the LAG issue. Use the closing temperature as your baseline setting, you can always reset it to any temperature you want you just want to have a consistent testing method.

I set mine at 70C, others are using 65C.

Get the temperature setting you want, then scratch some additional adjustment lines on the plate. If your setting is too low, then you can shift it to another line that adds a bit more pre-load. Or, if it is too high, shift it back to a lesser pre-load line.

You can take off the clutch, open it up, and shift the plate to a new setting without removing the fluid in the clutch.

If you want to bring in the fan as soon as possible, all you have to do is open the clutch, loosen the two adjustment screws, let the plate shift to the end of the adjustment slot (the pre-load on the bi-metal strip will move it for you), then tighten the adjustment screws, and bolt the clutch back together.

Mudança no marcador de temperatura

here are two components on the temp guage card. The tiny one is a Zener Diode and the bigger one is a resistor. What you do is to replace the Zener Diode by a 56 Ohm 5 watt resistor and replace the existing resistor by a 120 Ohm 5 watt resistor. These components are 30 cents each from Jaycar.

The results are excellent both in the truck and on a "test bed" involving the kitchen stove and a slowly cooling saucepan of oil.

The needle comes onto the gauge at 70 degrees. At 90 degrees the needle is in the middle, lining up exactly in the middle of the little thermometer symbol. At 100 degrees the needle sits exactly on the boundary between the white and red zone. Middle of the red zone is 110 degrees and end of red zone is 120 degrees. The needle moves progressively - in fact you can actually detect the thermostat opening when idling from cold.

The mod works well in conjunction with a different mod I did some months ago which was to wire the aux fan feed up to a lamp on the dashboard. This comes on at around 98 degrees so if I dont notice that the guage has moved to near the red I will when a bloody great red lamp lights up. The fact that the aux fan and temp guage senders are separate senders gives a lot of confidence

On normal driving the needle stays close to centre. But if the engine is loaded (all accessories on and driving up a long hill flat out, you see the needle move up and down between the middle and 3/4 positions (about 90 to 95 degrees). Simulating a failing radiator or a dodgy fan clutch by stuffing some cardboard in front of the radiator causes the needle to move quite quickly to the 98 degree position when the aux fan and red lamp kick in. I now see why so many owners get caught out with the unmodified guage and crack a head.

Having seen how the temp can increase, I strongly advise anybody to either fix the factory guage or install an aftermarket one.