DIY fan thermal coupling repair

In detail: do-it-yourself fan thermal coupling repair from a real master for the site my.housecope.com.

If you do not know how to repair the fan viscous coupling with your own hands, then you should familiarize yourself with this material. Most motorists, whose vehicles are equipped with such a device, recommend not to rush to throw it out, but to start repairing it. Most of them are sure that this is not so difficult to do. The first step would be to understand how this clutch functions, and then you can do repair work. As a rule, they begin to pay attention to the viscous coupling after the power unit overheats, but the thermostat functions normally along with other elements of the cooling system.

Do-it-yourself fan viscous coupling repairs sometimes have to be performed immediately after the car has not started at all for a long time, as well as for a number of other reasons. The installation of the clutch is carried out in order to make the fan run faster when the engine speed rises. Accordingly, the higher the temperature of the antifreeze, the faster the fan should spin.

Viscous coupling - this is the name of a device that is necessary in order to transmit rotation using a specialized fluid previously pumped into it. At its core, it is a one-piece chamber made of round, and inside it is a lubricant, the base of which is made of silicone. There is a pair of shafts in the chamber, and the principle of operation is as follows: the crankshaft rotates, transmitting force to the primary shaft of the clutch. The higher the load on the disc, the stronger the rotational speed will be, which means that the viscosity of the silicone will increase significantly.

The clutch will be blocked, and in the meantime, the second disc will begin to rotate, on the shaft of which there will be a fan cooling the radiator. Such properties are necessary in order to turn on the fan as soon as the temperature of the power unit begins to rise. With an increase in temperature, it will constantly turn on, and as soon as it reaches the desired level, it will turn off.

The clutch is actively installed on power units, as it has a high level of safety and reliability. If you use it not too carefully, for example, a hand gets into it, it will stop, but nothing will happen to the hand. That is, the blow will not be too strong.

Video (click to play).

In fact, there are not many such signs, but they still exist, and they should be dealt with. Most of the instructions say that you need to check how the fan functions on a cold engine and on a hot one. In the same literature, it is indicated that on a cold engine there are no serious changes in terms of speed, but on a hot one, there are still some changes - the frequency increases.

It is necessary to check the longitudinal backlash. If it exists, it must be gotten rid of. Noises during rotation will indicate that the bearings are broken. Probably, there are also certain problems with sealing-type oil seals - they could have worn out corny. One of the most common breakdowns is fluid leakage from the coupling itself.

Since the most popular type of breakdown is leakage, we will talk about it now. In order to refill the viscous coupling, it must be dismantled, and then disassembled. On the dismantled device, you can see a spring, under which a filler neck is located. When the sleeve is removed, pull the pin out of it, and add the missing lubricant with a syringe.As a rule, the best way to pour the clutch is usually the oil intended for the transmission.

When adding lubricant, it is recommended to put the coupling so that the filler neck is on top. It is enough for the syringe to contain about fifteen milliliters of oil. Insert the syringe into the holes and press it. You do not need to pull it out of the neck right away, you should wait a little. Now you can wipe off what has dripped onto the coupling, after which it is mounted in its place. That's it, the device can be installed back.

The fact that it is time to start such work is indicated by the noise that will come from the place where the fan is located. As already mentioned, in order to repair the viscous coupling, it must be removed. There is absolutely nothing complicated in this, because it is enough just to unscrew three bolts, after which it easily rises up.

Then you can replace the bearing. The procedure can only be done if the unit is disassembled and all grease has been drained from it. The liquid is then filled in with a new one, and the bearing is removed with a puller. Install the bearing carefully so as not to damage anything. This is how the fan viscous coupling is repaired by hand. If you want, you can do it in just a couple of hours. You don't even need to drive your car into the garage.

Since failures occur, many owners will be interested in learning how to repair a viscous fan coupling with their own hands. Many car owners with such a device advise not to rush to throw it away, but try to repair it yourself. According to many of them, this is not difficult to do.

To begin with, it is advisable to get acquainted with its device and the principle of operation, and only then proceed with the repair work. The reasons for which they begin to pay attention to the viscous coupling are usually engine overheating during normal operation of the thermostat and other elements of the cooling system.

Do-it-yourself fan viscous coupling repair often it is necessary to perform after a long idle time of the engine, its long-term operation, as well as for some other reasons. Its installation on an internal combustion engine has one goal, it is a smooth increase in fan speed as the engine warms up. With an increase in the operating temperature of the coolant, the fan speed should increase.

A viscous coupling is a device, the principle of operation of which is the possibility of transmitting rotational motion by means of a special fluid that is pumped into it. It can be thought of as a small circular chamber filled with silicone-based grease. There are two shafts inside this chamber, and the principle of operation is as follows. The crankshaft makes a rotating motion, which is transmitted to the first shaft of the clutch. With increasing loads on the disc, its rotation speed becomes higher, this leads to an increase in the viscosity of the silicone inside the coupling.

The clutch is blocked, which leads to the rotation of the second disc, on the shaft of which the radiator cooling fan is mounted. Another principle for turning on this device is the temperature properties of the injected silicone grease. These properties are used to turn on the cooling fan when the motor temperature rises. With an increase in temperature, it is turned on, and when it is lowered, it is turned off.

The widespread use of the clutch on modern motors is due to its high reliability and safety. In case of careless handling of it, when the hand enters the rotation zone, it stops without damaging the hand.

There are very few such signs, but they exist, let's try to understand them. Most manuals for the operation and repair of cars advise you to check how the fan rotates when the engine is cold and hot.It is also stated there that on a cold engine, no special changes in the rotational speed are noticed during gas overload, but on a hot engine, on the contrary, it increases.

It is necessary to check the longitudinal play of the fan of the clutch, if any, it requires treatment. The appearance of extraneous noise during rotation may indicate a failure of the bearings. Faults also include aging of the packing glands. However, the most common type of malfunction is leakage of silicone fluid from the coupling housing.

Since fluid leaks from the clutch most often, let's talk about it first. To replenish it, you need to remove the viscous coupling from the water pump, and then proceed to disassemble it. On the removed device, under the spring plate, there is a filler hole for the working fluid. On the removed coupling, the pin is carefully pulled out and the missing amount of liquid is injected with a syringe. Most often, it is recommended to pour transmission oil into the clutch.

When refilling fluid, place the sleeve horizontally with the hole facing up. Approximately 10-15 ml is drawn into the syringe. liters of transmission oil and without a needle insert it into the filler hole. Squeeze out the liquid and wait for some time without removing the syringe from the hole. After that, wipe off excess oil from the surface of the clutch housing and put the pin in its place. The product is ready for further use.

The signal for such an operation is the noise in the area of the radiator cooling fan. To repair it, the viscous coupling must be removed from the car. In most cars, it is mounted on a water pump pulley. This ensures reliable thermal contact with the coolant. It is necessary to unscrew the three bolts of its fastening, and it easily comes up from the engine compartment.

After that, you can start replacing the bearing. This operation can be performed only after complete disassembly of the unit and draining the liquid. In the future, it will be replaced with fresh one. The bearing must be removed only with a puller, otherwise the entire assembly may be damaged. After installing a new bearing, it is collected and filled with fluid.

Whatever happens, do not rush to throw away the old node and buy a new one, if it has not scattered at all. Do-it-yourself fan viscous coupling repair is an affordable operation that does not require special knowledge and tools. A bearing puller can be found from colleagues in the garage cooperative, the rest is not in short supply today.

The background is as follows: the engine began to overheat, the temperature went off scale to 110 degrees. Looking under the hood, I noticed that the fan rotates rather slowly for this temperature. Unfortunately, there was no newspaper at hand, I had to check it by hand - the fan stopped! (for safety reasons, it is recommended to check not with your hands, but with a newspaper rolled into a tube, if the thermal coupling is faulty, it will stop, if the newspaper is torn to shreds, everything is in order)
We skip the dismantling process, since there should not be any special difficulties (we unscrew three bolts with an internal hexagon securing the fan, then with a 36 key the thermal coupling itself).
And here it is in front of us - thermal coupling No. 111 200 04 22

(photo is not native)

After rereading the articles on the repair of thermal couplings, it was decided to try to revive it. The principle of its operation is as follows: a thermal spring located in the center of the clutch under the influence of temperature starts to move and moves the disk inside the clutch, which, in turn, drives the gel from one cavity to another, thereby forcing the clutch itself (and the fan, respectively) to rotate. It was not possible to find out the exact reason for its failure, and most likely this is due to the gel inside. Either it flows out, or evaporates, or something else. unclear. The optimal substitute for the gel was silicone oil PMS-100, which is sold in any radio parts store (our price is 150 tenge per 10 ml).3 10-milligram syringes were purchased with this oil. After long deliberation and studying the photos of the other coupling in the section, a place was chosen for drilling the hole for filling the oil. I read that on some couplings there is even a special hole for refueling, I did not find one on mine.Take a drill for 2.5 and drill

Pour oil into the resulting hole with a syringe

30 ml was poured (in different articles they write differently, from 20 to 50, I decided to try pouring 30)

After refueling, plug the hole by screwing in a bolt of the appropriate size. (The bolt used inside the computer's system unit to attach the floppy drive, motherboard, etc. was ideal.)

As you can see in the photo, I also removed the thermal spring, deciding to try pouring oil through the hole, removing the stem. But the stock could not be removed

After analyzing the comments of motorists on forums and social networks, it became obvious that drivers have a very abstract idea of such a simple and interesting in many respects device - viscous coupling. So, read the details about the principle of operation, checking and self-repairing the viscous coupling.

Viscous coupling — it is a special device that rotates the cooling fan thanks to a special fluid. It has a round shape with a silicone base filled with grease; serves for smooth fan control. At first glance, the principle of operation will seem complicated, however, if you look at it, this is not so: the crankshaft rotates, transferring energy to the first shaft of the clutch. The device then accelerates, which makes the silicone inside it more viscous. The clutch is blocked, after which the second disc begins to rotate, on which the radiator fan is located.

The viscous coupling is used on almost all motors, since the device is reliable and safe. If a hand is inserted into a moving mechanism through carelessness or inexperience, the device will stop, thus preventing injury.

After a long period of inactivity of the car, the viscous coupling needs an oil change, as well as a check of the condition and operation in general. In addition, failure is possible due to wear or some other reason.

It is quite difficult to recognize a breakdown of a viscous coupling, but there are ways to check its performance.

Look at the speed of the device when the engine is cold and hot. In the first case, strange sounds are usually not observed, and the number of revolutions is correct. With a hot engine, the picture is different: extraneous noises are heard, and the rotational speed of the viscous coupling may not correspond to the norm.

Various noises are often caused by faulty bearings. Also, the cause of the device malfunction may be the gland seal, or the leaked special silicone fluid.

If you notice engine overheating, do not rush to do replacement viscous couplings. You may be able to repair the broken part yourself.

The most common cause of failure is silicone leakage from the base of the part. To fill in new fluid, you need:

Remove the viscous coupling from the water sediment, and then disassemble it.
On the disk of the device itself there is a plate with a spring, under which there is a hole for the silicone fluid. You need to use the utmost care to remove the pin, and then fill with a syringe with grease. Keep in mind that during such a repair, the part is laid horizontally.
It is enough to draw fifteen milliliters of oily liquid with a syringe.
Slowly pour the silicone inside.
Wait a few minutes without removing the syringe from the hole, so that the liquid has time to deeply flow into the viscous coupling.
Wipe the surface of the device from excess liquid if necessary.
Replace the pin and then install the part.

If you are not well versed in cars and do not know how certain parts work, it is better not to start repairing yourself. The point here is not the possible breakdown of parts of the vehicle, but the difficulty of putting everything back together.

Also, bearings are a common cause of viscous coupling failure. There is only one symptom of such a malfunction: various kinds of noises in the area of the cooling radiator.

To repair the device, the first step is to remove it. To do this, unscrew the three bolts that secure the part. After that, the viscous coupling can be easily removed from the engine compartment.
After removing the device, you can start replacing the bearing. Replace them only when you have disassembled the unit and drained the oil fluid. Use a special tool to remove the bearing - a puller. If you use the tools at hand, you can completely damage the node.
Having installed a new bearing, you can start installing the device. Do not forget to fill in new silicone fluid, which was drained before repairing the viscous coupling.

When you notice a "misbehaving" of a coupling, you do not need to change the entire part right away, as it can often be repaired. Special skills and abilities for this business will not be required.

The only difficulty that can arise is finding a puller to remove the old bearing. The tool is not sold in every car store, which makes it difficult to repair the viscous coupling on your own. If you have visited all the car dealerships you know and did not find a puller, ask your friends-drivers. The rest of the details are easy to find.

Not all such devices have a hole for filling oily liquid. If you are a "beginner", do not try to repair the device yourself. Experienced craftsmen make the holes themselves. You can, of course, also try drilling the hole at your own risk.
Do not use brute force when handling the disc. If the aluminum on the currency is bent, the viscous coupling cannot be repaired - only a complete replacement of the device.

Open the hood of the car and flip out some of the fan housing latches.
Unscrew the bolts with a 6-point hex wrench.
Remove the cooling fan.
Rotate the cover 180 ° to the right. There is no other way to remove the part. Therefore, it will not work to get to the viscous coupling.
Unscrew the viscous coupling with a 36 wrench. The tool jaws should be no thicker than 10 millimeters.
After taking out the device, clean it from dirt and dust.
Next, you need to rivet the bimetallic plate of the viscous coupling on one side.
Pull out the part disk and fill with a syringe with PMS-100 lubricating fluid.
Assemble the viscous coupling structure back; install the device in the car.

There are no fundamental differences in removing the device. You need to unscrew three screws securing the impeller and then three more to remove the cover.
Then, taking out the viscous coupling, carefully remove the upper disc, which serves to block the fan.
The entire device is lubricated with special oil. Repair the viscous coupling to preserve it. If you do not know the exact name of the liquid, it will be extremely difficult to find it.
Simply replacing the bearing will not work, since you first need to grind off the flare on the shaft.
Place the device in a vise for greater ease of repair.
The bearing also needs to be ground off. If this is not done, the base of the viscous coupling can be severely damaged.
Buy a sealed type bearing with no visible balls at any automotive store. Its cost is not more than 100 rubles.
Before seating the bearing, coat the seat with sealant.
Assemble the viscous coupling and then install it in the car.

The name of such a detail, and even more so how it looks, is not known to many. Basically, car mechanics and mechanics are engaged in repair and replacement.Experienced craftsmen make repairs with their own hands, for example, for a rigid connection with a fan shaft, holes are drilled in a viscous coupling, a thread is cut with a tap and bolts are screwed in. Let us examine in more detail what a viscous coupling is, signs of malfunctions, and methods of self-repair.

Viscous coupling, it is also a viscous muff (from the Latin viscosus - viscous) is a mechanical device that transfers torque using a viscous fluid.

In this video, see what is the clutch in the cooling fan device

The principle of operation of the viscous clutch is carried out thanks to the belt drive, which connects the clutch rotor and the crankshaft pulley of the internal combustion engine. Also, there are car designs in which the clutch is installed directly on the crankshaft or camshaft. Image - DIY fan thermal coupling repair

Spring.
Bimetal plate.
Inlet B.
Intake duct A.
Camera.
Check valve.
Check valve.
Rear springs.
Front reservoir.
Rotor.
The body of the device.
Rotor shaft.
Bearing shell.
Rear reservoir.
Back plate.
Rotor.
Front plate.
Lid.

Due to the complex design of the device, the price of a viscous fan coupling is relatively high.

In cars where rare models of the clutch are installed, if it is impossible to repair it and find a new such mechanical unit, the owners have to slightly re-equip and install an electric cooling fan.

This video simply and clearly shows how to determine whether a viscous coupling is working properly or not. We do not miss the opportunity to glean useful information, look:

The resource of this device in the design of the machine is designed to cover 200 thousand kilometers. Image - DIY fan thermal coupling repair

To check if the fan and clutch are working well, you need to know the symptoms of faults in these parts:

If the engine heats up quickly, then this is the first sign of a viscous coupling malfunction. This appears due to the release of the gel or the inopportune actuation of the bimetallic plates. In this situation, when the motor is very hot, the fan or rotates at a low speed, or does not turn on at all.
The cooling fan starts spinning when the engine is still cold. This is due to a change in the properties of the gel, solidification of the lubricant and the failure of other elements of the viscous coupling.

A resource has been developed.
Mechanical damage.
The bearing has worn out or broke prematurely.
End runout of the fan impeller. Part of the propeller blade is broken.
Lack of lubrication of the coupling shaft.
Dirty coupling joint.

More reliable fan with viscous coupling than electric fan. It often happens that after winter, the fan electric drives fail and the electronic control circuit of the propeller is disrupted.

The advantage of the viscous coupling is that there is no electronics or electricity in it.

The viscous coupling provides more power, the fan rotates at a higher speed. If the clutch sits rigidly on the engine crankshaft, then the rotation speed is very high.

The power of the clutch connected to the crankshaft is several kilowatts (kilowatts). And the power of electric fans has a capacity of several tens of watts. Due to this, it is the viscous coupling fan that is used in agricultural machinery, military equipment, and special equipment.

Complex structure, more difficult to make repairs. It is cheaper to buy a new assembly.

Has a good mass. The weight on the ICE crankshaft is significant.

The temperature control of switching on is not entirely correct. There are errors in turning the cooling fan on and off.

There is an increased noise level at high revs.

According to the schedule, you have to refuel with gel or oil with the desired viscosity.

The viscous coupling takes up part of the engine power.

This list of viscous coupling shortcomings influenced the decision of the owners of auto concerns. They abandoned the use of such devices in passenger cars.If this device stops working, then first you need to fill it with gel or special oil.There are not many specialists who can fix a viscous coupling. Sometimes it’s cheaper and faster to buy a new device or switch to an electric fan.

Replacing the old one and installing a new viscous coupling is an easy job, even a beginner can do it. After dismantling the device, it is necessary to remove the fan impeller. Install a new clutch. When installing a new coupling, the bolts must be tightened firmly, but without stripping the threads. Then you need to install the fan in place.

I am writing a milestone time, about the fact that this topic was discussed milenon times!

The clutch is not repairable! It is not known where to look for such oil.
It remains only to throw it away.

Toyota Mark II E-GX100
2.0 Grande 1G-FE - Sold Out

Renault Duster 2.0 4 × 4 waiting

My temple was simply jammed, spun and cooled even at -15 overboard, so I drove for a while without a fan at all - it was very noisy.

Today I decided to return everything back, for some reason, having previously repaired the clutch. To begin with, I figured out the device and the principle of operation.

It is arranged simply, I will not go into details, I will only touch on the locking mechanism. It consists of a bimetallic spring fixed on the clutch housing and on a movable outlet from the clutch. The spring has a spiral structure, but when heated, it does not twist, and does not unscrew - but pulls the movable pin up (if it is necessary to block) and down (when unlocked). Accordingly, the malfunction was that the spinach was clogged with mud and did not move at all.

Solution: It is necessary to carefully remove the spring, or pry it from below, pouring brake air onto the spinning pin and develop the spinning pin. And that's all. The liquid inside is eternal, if it has not flowed out - so everything is fine, you shouldn't even climb inside.

At the moment, the clutch is working normally, it turns on for a cold one for 10-20 seconds, then it turns off itself and remains in this state until the need for cooling.
So go for it. It's simple!

Radiator fan viscous coupling theory

How is a Toyota fan clutch and how does it work? Since this topic still raises questions at times, let's try to figure it out.

A belt-driven fan, usually combined with a coolant pump, has traditionally been installed on most longitudinal powertrain models. If the fan impeller was rigidly connected to the drive pulley, then its rotational speed was directly proportional to the crankshaft speed - such cooling would be excessively effective, especially at high speeds and at low temperatures overboard.Therefore, to adjust the intensity of the air flow passing through the radiator, a viscous clutch is installed between the pulley and the impeller.

At low temperatures, the fan speed is minimal, which allows the engine to warm up faster and at the same time reduces the noise from the impeller. As the temperature rises, the fan speed will also increase.

The clutch rotor is rigidly attached to the coolant pump pulley. Along the circumference of the rotor disc, oblique teeth are cut, which act as a pump for pumping oil. The clutch housing assembly (bearing housing and front cover) rotates around the rotor on a bearing.

On both sides of the rotor, plates are installed that separate the working chambers from the reservoirs. The front (with inlets A and B and the return channel) is fixed to the rotor cover, the rear (with the return channel) is fixed to the bearing housing.

1 - bimetallic spring, 2 - bimetallic plate, 3 - inlet B, 4 - inlet A, 5 - front chamber, 6 - return channel, 7 - return channel, 8 - rear chamber,
9 - front reservoir, 10 - rotor teeth, 11 - bearing housing, 12 - rotor shaft, 13 - bearing housing, 14 - rear reservoir, 15 - rear dividing plate, 16 - rotor, 17 - front dividing plate, 18 - front cover ...

Working chambers are “labyrinths” formed by ribs on the rotor and on the dividing plates. The torque is transferred from the rotor to the housing by means of “internal friction” in the silicone oil.

A bimetallic spring mounted on the outside of the clutch housing moves the plate, opening and closing the intake ports and adjusting the oil flow based on the air temperature.

1. Cold air.
When the rotor rotates, its teeth through the return channels “pump out” oil into the front reservoir from both chambers and the rear reservoir. As a result, its amount in the chambers decreases, the transfer of force through the liquid decreases, and the fan speed becomes much lower than that of the main rotor.

2. Warm air.
Centrifugal force forces the oil from the front reservoir into the front chamber through the open inlet A. “Viscous friction” between the rotor and the front plate increases and the speed difference decreases.

3. Hot air.
Both inlet channels open, after which oil flows into both working chambers. The volume of fluid in them and "friction" are maximum, so that the transmission of rotation through the coupling is also maximum.

Note. Since the speed control is due to a change in the volume of silicone oil in the cavities of the clutch, its leakage inevitably leads to a decrease in the fan speed and possible overheating of the engine.

Some couplings of the early design did not have a rear reservoir. Since after stopping the engine oil flows down to the lower part of the clutch, here its level in the chambers increased significantly, and immediately after starting the engine, when the “friction” between the rotor and the plates is high enough, the fan speed increased too much. If there is a rear reservoir, the liquid level in the chambers with the engine stopped is lower, and after starting it drops faster - as a result, the noise level from the fan is reduced.

A viscous clutch in the cooling system of a car engine is used as an alternative to an electric fan. Consider how the fan viscous coupling works, its structure, possible malfunctions, advantages and disadvantages.

The viscous fan is installed on vehicles with a longitudinal engine arrangement (usually all-wheel drive and rear-wheel drive models). With this arrangement, the radiator fan pulley is best connected to the water pump pulley. As you know, the rotation of the water pump is transmitted by the service belt from the crankshaft pulley.

The disadvantage of this design is that the fan impeller speed will always be proportional to the crankshaft speed. Such a device will lead to the fact that at high speeds in cold air conditions, the engine will be excessively cooled, which will reduce its efficiency. In addition, the permanent connection of the impeller and the crankshaft pulley will increase mechanical frictional losses, which will consume power and increase fuel consumption.

The viscous fan coupling allows you to adjust the impeller rotation speed depending on the engine temperature.

The difference in the design of viscous fan couplings Toyota, BMW, Mercedes, Audi. is minimal, since they are all arranged and work according to the same principle. Image - DIY fan thermal coupling repair

The shaft with the connecting flange is attached to the drive of the cooling pump, therefore its rotation speed is always proportional to the crankshaft speed. A drive pulley is attached to the shaft, which rotates in the working chamber. The working and reserve chambers are separated by plates. The transition between the chambers is possible only through the inlet valves and return ducts. The storage chamber is initially filled with a special silicone oil. The drive pulley, or disk, as it is also called, has oblique teeth around the circumference, which, when rotated, allow the oil to be expelled back into the backup chamber. The surface of the drive discs, like the dividing plates, has special ribs that turn the working chamber into a kind of network of labyrinths through which silicone oil circulates.

The clutch housing, to which the fan impeller is attached, is connected to the shaft (viscous coupling rotor) by means of a conventional ball bearing. The intake valves are connected to a bimetallic plate, which is located in the front of the viscous coupling housing. When heated, the plate expands, which leads to an increase in the flow area of the valves.

The main feature of the silicone fluid used in fan viscous couplings is heat resistance and viscous stability. With a change in temperature, the oil only slightly changes its viscosity.

In the operation of the viscous coupling, silicone oil acts as a binding agent, which allows friction to be created between the drive disc and the spacer plates connected to the housing. Although there will always be some degree of slippage between the housing and the drive pulley, the friction coefficient created is sufficient to engage the clutch housing with the drive shaft.

Some sources indicate that as the temperature rises, the oil expands, which provokes the viscous engagement of the drive disc with the viscous coupling housing. Such an understanding of the principle of operation of the viscous coupling of the cooling fan is false and arose, most likely, due to the comparison of the viscous coupling of the fan with the viscous couplings of the transfer cases of all-wheel drive vehicles. In the viscous couplings of the differentials, a dilatant fluid is used, the viscosity of which is highly dependent on the shear strain rate.

When the working chamber is not filled with oil, the drive disc rotates freely in the working chamber. A small amount of oil is still present, but the coefficient of adhesion of the drive pulley to the viscous coupling housing is minimal, therefore, with an increase in engine speed, the impeller speed does not increase.

The process of warming up the engine and increasing the temperature of the antifreeze in the radiator is accompanied by the heating of the bimetallic plate. As the plate heats up, it expands, which leads to the opening of the inlet valve and an increase in the amount of working fluid that penetrates from the reserve into the working chamber. Friction between the drive disc and the spacer plates increases the speed of rotation of the casing and fan impeller.

When the engine needs maximum cooling, the bimetal plate is bent enough to provide maximum intake valve bore.In this case, the difference in the rotational speed of the shaft and the viscous coupling housing is minimal, therefore, an increase in the crankshaft speed leads to an almost equivalent increase in the rotational speed of the fan impeller.

A decrease in the temperature of the incoming air leads to a gradual return of the bimetallic plate to its original position. Accordingly, the flow area of the intake valves decreases, the liquid is distilled into the reserve cavity. A decrease in the adhesion coefficient leads to an increase in the difference in the speed of the drive shaft of the viscous coupling and the housing - the fan impeller slows down.

The device of viscous couplings of Toyota fans assumes the presence of two working chambers (in the first versions of the design there was only one chamber).

Bimetallic plate in the "cold" state.

The plate is heated with warm air, the inlet valve of the front chamber is open.

The coefficient of thermal expansion corresponds to the maximum cooling mode. Rear chamber valve open.

Many owners of cars with a mechanically driven cooling fan are likely to notice that after starting a cold engine, the fan rotates at a high speed. Some time after the engine warms up, the number of impeller revolutions decreases, so it may seem that a similar phenomenon goes against the above-described principle of operation of the fan viscous coupling. This effect arises due to the fact that during idle time the oil flows by gravity into the lower working chamber, therefore, immediately after starting, the impeller and the viscous coupling housing will rotate until the oil is pumped back to the reserve section.

The impeller speed is adjusted to the actual temperature conditions of the engine, which allows:

reduce fuel consumption;
reduce the noise level;
reduce power losses.

Installation of a viscous coupling in the cooling system allows you to reduce the load on the generator and reduce the cost of the car, eliminating the cost of the impeller electric drive and wiring.

Video (click to play).

Many complain about the unreliability of the viscous coupling, forgetting that the system with an electric fan also needs to be periodically repaired. The most common failure is fluid leakage. Despite the fact that most of the viscous type couplings are non-separable, there are proven technologies for restoring the system to work. In case of wear, the bearing is also recoverable. That is why it is important to know how to check and repair the viscous coupling of the radiator fan.