The principle of operation of the viscous cooling fan UAZ Patriot

How the device works

It was invented in the USA in 1917 by engineer Melvin Severn. This product did not immediately find its application, so it was not recognized for a long time. In 1964, a viscous coupling was installed in the Interceptor FF, where it acted as an automatic differential lock. Only in 1965 did this mechanism take its place in the engine.

A viscous coupling is a device that is responsible for rotating a special fan that cools the system thanks to a special liquid. It looks like a round mechanism made of a silicone base and filled with a lubricant. The viscous coupling ensures smooth fan control.

There are flat disks inside the product body. Some of them are connected to the drive shaft, while others are connected to the driven shaft. There are various protrusions and holes on their surface. Design features place these elements in close proximity to each other. The silicone liquid located inside tends to thicken with strong stirring. It also expands when heated, so it creates a lot of pressure on the disks when the engine is running and compresses them together.

Features of the mechanism

At first glance, the operating principle of a viscous cooling fan coupling seems complicated, but it is not. The movable crankshaft is driven into rotation and transfers its energy to the clutch. This makes its silicone base softer and more viscous. The clutch begins to block, causing the second disk with the fan to rotate.

Almost every engine has a viscous coupling. This is due to the importance of its functions and the quality of the device, because it is at a fairly high level. The viscous coupling has an excellent safety mechanism: when a person, through his own negligence, puts his hand into the moving element, he will stop to prevent injury.

The essence of the problem

Let's start with the fact that the engineer of the Ulyanovsk Automobile Plant equips UAZ Patriot SUVs with radiator cooling fans, which are driven by a viscous coupling.

A viscous coupling is a mechanism presented in the form of two flat disks. Viscous coupling allows you to transmit torque using a special silicone-based fluid.

The operating principle consists of several plates mounted on the driven and drive shafts. They rotate in a container with liquid, which changes its properties when heated. When the liquid is mixed while the drive shaft rotates, it changes its properties (expands) and thereby creates pressure in the chamber. As a result, the disks of the driven shaft engage, causing it to move.

This viscous coupling drives the fan on the UAZ Patriot SUV. Everything would be fine if it were not for such a minus, which gives impetus to the search for its elimination. This disadvantage is that the viscosity of the liquid depends on the mixing speed. When the UAZ Patriot vehicle is braking and the engine is idling, the fluid loses its properties as a result of the rotation of the drive shaft slowing down. This causes the cooling fan to slow down and the temperature in the engine gradually rises. This phenomenon occurs when you have to stand in a traffic jam in the summer heat or move over rough terrain at low speed. Although the viscous coupling is an innovation, its use on the UAZ Patriot SUV is unsuccessful. We will look at how to eliminate the problem of engine overheating below, but for now we will list the disadvantages of using a viscous coupling.

Flying impeller blades

Disadvantages of viscous coupling

The disadvantages of using a viscous coupling on a UAZ Patriot SUV include the following factors:

Engine temperature instability, which varies depending on crankshaft speed.
Engine load.
Difficult access to rollers and belts.
There is no way to force the engine cooling fan to turn on.
Inconsistent fan speed. It is possible that the fan blades may come off, which could result in a hole in the radiator. As a result, it becomes necessary to replace the radiator and install a new fan.

There is no way to repair it. If the product does not function, then repair is no longer appropriate and it must be replaced with a new one.

Theoretically, it is impossible to repair the product, but in practice it is possible. To do this, two holes are drilled in the viscous coupling hole, through which bolts are threaded and fixed to the drive disk. This repair allows the fan to rotate regardless of changes in fluid viscosity.

To get rid of this problem, it is necessary to install an electric fan instead of a viscous coupling. Such a system is much more reliable, efficient, and, most importantly, rational. We will consider the advantages of such a system further.

Electric fan instead of viscous coupling: advantages

The advantages of installing an electric fan instead of a viscous coupling are:

Maintaining a constant engine temperature.
When the car is stopped and idling, the engine does not heat up.
This frees up access to the belt and rollers, making them easier to replace.
Possibility of manually turning on the electric engine cooling fan.
In addition, if one fan fails to cope or it breaks down, then in this case two units are installed, which compensate for each other’s work if necessary.

So, we found out that instead of a viscous coupling for cooling an SUV engine, it is rational to install an electric fan. To do this, you need to remove the viscous coupling from the UAZ Patriot SUV.

Removing the viscous coupling

Removing the viscous coupling is not particularly difficult and can be done with your own hands if you have the necessary tools. But you still need to know the process of removing the product and some important points. So, removal of the product is carried out in the following order:

First you need to remove the fan shroud. Let's take a closer look at how to do this:

Using a small screwdriver, you will need to remove the spacer clamp pins. They are located on the top of the casing.
The clamps are then removed.
The casing is removed by lifting it up.

Checking the cooling fan

It is not always possible to use the car regularly, so it ends up in a state of downtime. At this time, the viscous coupling requires checking its performance. This will also help prevent damage from wear and tear.

Recognizing a malfunction is not easy under normal conditions, but there are methods for checking the viscous coupling of a fan. To inspect the mechanism, you need to check the speed of the product with the engine turned on, warm and cold. When the engine is cooled, there should be no extraneous sounds, and the speed should be normal. A hot engine can often provoke various noises and irregularities in the speed.

Such problems can arise due to faulty bearings or untimely oil changes. Also, sealed seals and leakage of silicone fluid can cause failure.

Solving the problem yourself

If defects in operation are found, the viscous coupling does not always have to be replaced. These problems can often be solved on your own. One of the most common problems encountered with this device is silicone fluid leakage. To make up for the deficiency, you need to do the following:

Disassemble the viscous coupling by removing it from the water pump.
It's worth taking a closer look at the product's disk. On its surface there is a special plate with a spring, under which there is a hole for silicone. It is necessary to remove the pin with extreme caution and pour lubricant inside using a special syringe. During this process, the part itself must be placed in a horizontal position.
It will be enough to pour 15 milliliters of liquid into the syringe.
You need to wait a few minutes until the substance flows into the viscous coupling without removing the syringe.
After checking that the procedure was performed correctly and that there is no excess silicone, the part can be installed back.

For those who do not consider themselves experienced motorists, it is better not to engage in such work, because this can cause complete breakdown of the device. Typically, the biggest challenge is putting everything back together.

Operating principle of viscous coupling

What is a viscous cooling fan coupling? This is a special mechanism that performs the function of selective transmission, which depends on external conditions and torque. The viscous coupling looks like a housing that is completely sealed, with two rows of discs located inside. One of them is connected to the driven shaft, the second to the driving shaft. These disks are interleaved with each other. Each of them has both holes and protrusions, and the distance between the planes of the disks is minimal. The viscous coupling body is filled inside with a viscous liquid, which is often made on a silicone basis. Viscous coupling fluid has specific features that allow it to be used effectively.

These are: An increase in viscosity with increasing stirring intensity. High coefficient of expansion during heating. When the car moves at a constant speed, the viscous coupling discs rotate evenly and the oil does not mix between them. When the speed of the driven and drive shafts differs, the speed of rotation of the disks also differs. As a result, the viscosity of the fluid increases, and it affects the transmission of torque to the driven shaft. When the disc rotation speed difference is very large, the viscous coupling oil becomes so viscous that it becomes blocked. The liquid turns into a state close to solid.

Features of repair work

As some motorists may have noticed, the viscous coupling does not always have a hole for filling silicone fluid. In this case, you can do it yourself, but beginners should not do this so as not to damage the product. It is better to turn to craftsmen who will do careful drilling.

Repair of the viscous fan coupling should be carried out without brute force. The main material of the device is aluminum, which can simply be bent and completely destroy the viscous coupling.

The operation of a car depends on many mechanisms that must work as a whole. If even one element fails, the serviceability of the entire vehicle is disrupted. The viscous coupling is necessary for the normal operation of the cooling fan. The safety of the trip depends on this, so you need to monitor its performance.

Repairs to the viscous cooling fan coupling should only be carried out by specialists. Of course, you can do this yourself, but any mistake can damage the device. You need to take care of service work in advance.

Repair and replacement of viscous cooling fan coupling

In fact, viscous coupling repair consists only of replacing the bearings. If a characteristic hum or any similar sound appears when the fan operates, then the bearing needs to be replaced. First of all, you need to remove the fan from the drive mechanism. Most often, the drive of such a cooling fan is a pump, since it has closer contact with the coolant and, accordingly, more successfully transfers the coolant temperature to the viscous coupling.

Unscrew the three bolts securing the fan to the pump. After this, the fan is pulled out from above and disassembled. The fluid is drained and will be replaced with a new one in the future. Installation of the bearing and its pressing is carried out using a special puller or press. The use of percussion instruments is strictly prohibited. After replacing the bearing, new silicone liquid is poured in, and the fan is assembled in the reverse order.

Replacing a viscous coupling is much easier, which is an excellent and not very expensive alternative to repairing a damaged mechanism. Replacement occurs in cases where the liquid loses its properties and the fan does not work or when it begins to leak, which indicates poor sealing of the entire assembly. To change the coupling, you need to unscrew its entire assembly from the impeller and install a new one in its place. Thus, the viscous coupling of the car engine cooling fan is replaced.

As you can see, this is not a complicated procedure and is performed on your own with a minimum of effort and money. Therefore, problems with viscous couplings can be solved independently without the help of employees in the automotive service and repair industry.

How to check a viscous coupling

Step-by-step instructions for using a tachograph with a driver card

The performance of the viscous fan coupling must be checked on a cold and hot power unit. This is evidenced by operational manuals for vehicle repairs. When the engine is cold, re-gassing will not change the clutch rotation speed. In the case of a hot engine, this figure will increase significantly.

It is also necessary to check the longitudinal play; if it is detected, work will have to be done to eliminate it. The presence of extraneous sounds during clutch rotation will indicate a bearing malfunction.

Main causes of malfunction

The mechanism can fail for several reasons. We have identified the main and most common:

the use of tires of different sizes, which also have different levels of wear;
fluid leakage from the coupling;
wear of parts as a result of intensive use, exposure to aggressive factors and high temperatures;
incorrect alignment of the drive mechanism;
loss of properties of the bimetallic sensor, which can occur as a result of surface oxidation and jamming of the coupling;
faulty bearing condition.

Intake viscous coupling of an Infiniti car

Symptoms of a problem

The first and main sign that may indicate a faulty viscous coupling is excessive heating of the motor. This situation may occur as a result of a liquid leak or the failure of the bimetric plate to operate in a timely manner. The motor temperature rises, and the fan does not work at all or operates at low speeds, therefore, the unit is not cooled.

It also happens that when the engine is cold, the fan rotates at full speed. This situation may arise due to a damaged gel, breakdown of a number of mechanism components, or transformation of the lubricant into a solid substance.

What can a faulty viscous coupling cause?

The working reserve of a viscous coupling is on average 200 thousand km. After this, the mechanism requires increased attention. It is necessary to constantly monitor the moment of its operation, especially in the summer. It is also necessary to check the operating temperature of the engine in traffic jams. If values close to critical are observed, then you will have to seriously work on the viscous coupling. A new part costs a lot, and finding the right model is often not possible. That's why many car owners decide to install an electrical system. In any case, this situation cannot be ignored, since you may encounter the following troubles:

motor overheating;
reduced pump life;
increase in fuel consumption.

Each of you has been warned about the danger posed by a faulty viscous coupling of a car cooling system fan. Do not neglect checking and troubleshooting, otherwise you may face very expensive and time-consuming engine repairs.