The fan is one of the many components in the motor car which functions unnoticed and unthought-of of until something goes wrong. It has a simple but crucial job to do in a water-cooled engine. It boosts the draught of cooling air through the radiator, so keeping the engine at its correct working temperature. The time when the fan is needed most is when the engine is being run at low speed or when the car is stationary in traffic. In these conditions there is little air flow over the engine. It is at these times that trouble is often first noticed as a result of the radiator boiling over.
There are four principal types of fan that will concern the owner of a classic car. The most widely used on post-war cars was the simple belt-driven fan which operated whenever the engine was running. There are two basic modifications of this design. One incorporated a viscous coupling, while the other was controlled electro-magnetically. These both had the advantage of operating only at slow engine speeds. The fourth type of fan was the electrically-driven fan operated when necessary by a thermostatic switch.
Servicing a Conventional Fan
In its simplest form the fan is a multi-bladed metal device driven by a V-shaped belt from the crankshaft. Generally it is bolted directly to the exterior of the water pump and driven by the same belt which also drives the generator or alternator. This classically simple arrangement was used for decades because it was simple, cheap and relatively trouble-free. The major cause of problems with this set-up was a loose or broken fan belt. The V-belt drove the fan through a pulley system by friction, consequently, as the belt stretched through wear, it could start to slip. Tell-tale signs were overheating in traffic, as the fan and water pump were not turning at the correct speed. If the belt also drove the generator a final warning would, on older cars, be a red ignition light coming on indicating a failure to charge the system, but the belt may have been loose for some time by then.
The good news is, if you own an older car with this type of
cooling fan, adjustment is simple. One of the pulleys will have some form of adjustable mounting. Usually it is on the generator or alternator where there is a slot instead of a bolt hole for the fixing bolt. This allows the unit to pivot when the remaining fixing bolts are slackened. Moving the generator away from the engine will then tighten the belt and it should be adjusted in this way until there is approximately 12 mm of downward deflection possible in the longest run of the belt. When performing any kind of overhaul of the fan it is sensible to replace the fan belt or at least to check it properly for fraying and cracks. Even if the old belt is not too badly worn, replacing it will give you a handy spare which could prove very useful. A new belt will stretch considerably after you first fit it, particularly if it drives a lot of ancillary equipment, so it should be checked after the first few kilometres.
The simple metal-bladed fan requires little attention itself, but if you are working in that area of the car it is worth giving it a few checks. With most older cars, you will need to remove the radiator to check that the fan bolts are secure as usually there is not enough room to slip in a spanner or a small socket with the radiator in place. A fan blade spinning at 3,000rpm could inflict a lot of damage if it flew off so make sure it is firmly located. Examine the blades for trueness. Sometimes they can be buckled by a stone thrown up from the road, although the fan is usually well protected by the car's under-tray. Look at the fan while it is spinning; any bent blade or uneven running will be quite apparent. Gentle bending with self-locking grips or pliers may be sufficient to straighten a blade, but the shape is quite complex so if it is badly distorted it is best to replace it. Removing this type of fan is simple enough. It can often be done without removing the radiator, but this will depend on the accessibility of the bolts holding the fan to the pump and the clearance between fan and
radiator.
If The Radiator Has To Be Removed
When small engines are fitted into large engine bays there is often a cowling to duct the air through the radiator and on to the fan. This is generally a simple, light device located by small bolts or self-tapping screws to the radiator surround or nearby bodywork and can be removed fairly easily. The next step is to slacken off the fan belt. The bolts locating the fan blades hold the fan pulley in place as well, so slackening the belt reduces the strain on them. Then remove the blades, but remember which way round they go for when it comes to replacement. In common use was a nylon version of the simple fan. It was generally moulded in a single, multi-bladed unit, and was slightly flexible to make it less prone to damage from flying objects. It was fastened and removed in a similar fashion to the metal unit.
These simple fans have their limitations, however, the chief one being that they absorb a sizeable amount of engine power (4 to 5 bhp on an average car) which could otherwise be used in giving improved performance or better economy. Moreover, for a large proportion of the time the engine is running the fan is not required at all. It is only really needed for cooling purposes when the car is stationary or being run at low speed. So several different systems have been devised to cut out the operation of the fan when it is not required. These fans are a little more complex to service but should pose few real problems if care and common sense are used.
Servicing a Viscous-Coupled Fan
The viscous-coupled fan makes use of a natural property of fluids which is that a liquid has only a limited tendency to stick to itself, a tendency which is greater in proportion to the thickness of the liquid. This property is employed on viscous-coupled fans by the provision of a barrier, in the form of an oil-like fluid, between the inner face of the fan, which is attached to the water pump, and the outer face which is attached to the fan itself. As the water pump and inner face is turned by the fan belt so this motion is transferred to the fan through the fluid, which is dragged round with the inner face by its own viscosity. But as the speed of the pulley builds up, usually to 1,000 rpm, the fluid's viscosity is not enough to hold the two faces together. So, even though the inner face spins the fan does not spin with it.
The viscous-coupled fan is a neat and effective system. It cuts out the fan or slows it right down and reduces both fan noise and the drain on engine power. The coupling is almost invariably housed in a specially designed unit, the fan blades being separately fitted nylon blades. It is a factory-sealed, maintenance-free unit which hardly ever fails. A quick spin of the fan blades with the engine switched off will show if it is working. The blades should run easily on their fluid face. You should also look for any signs of a fluid leak round the coupling. Should there be any problems then the coupling must be replaced. However, due to the complexity of the fan and coupling assembly it is unlikely that you will be able to replace the coupling separately. In fact most manufacturers did not supply spare parts for these fans so the complete assembly had to be renewed as a balanced unit.
Removal of a viscous-coupled fan was similar to that of a mechanical fan. The viscous-coupling was effectively the hub of the fan and was secured to the water pump shaft by a single centre bolt. After slackening the fan belt to relieve the strain on the system, the fan and its viscous-coupling can be removed by undoing this single bolt. Depending on the amount of clearance present you may have to remove the radiator first. If the bolt seems unusually tight, try turning it clockwise; the bolt may be on a left hand thread to prevent it from being thrown loose by the running of the engine. On re-assembly it is a good idea to apply a little locking fluid to the bolt to prevent it vibrating loose. Having removed the whole unit, the coupling can be separated from the fan blades by undoing a ring of bolts which join the two components. Replacement is the simple reversal of the dismantling procedure.
Servicing an Electro-Magnetic Fan
The electro-magnetic fan performs the same function as the viscous-coupled fan but in a more complex way. It is operated by a temperature-sensitive switch which is located in the base of the radiator. Above a certain temperature it switches current through a carbon brush touching the back of the water pump pulley. This brush bears lightly on a coil of wire and with current flowing through it, it becomes an electro-magnet. The fan, in front of this pulley, is pulled by the magnet and clamps to the pulley and begins turning with it. With the fan in operation the water temperature obviously drops. When it reaches a certain point the thermo-switch is turned off, the electromagnet cuts out and the fan separates from the pulley and freewheels to a halt. Being rather complex there is quite a lot that can go wrong with this system.
If it has failed, the first thing to suspect is the brush located behind the water pump pulley which is located in a quickly-detachable, spring clip holder. This brush is prone to corrosion and wear and if it is not touching or is barely touching the pulley, it should be replaced. The other most likely fault is that there is too large a gap between the fan assembly and the hub pulley. This is a critical gap; if it is too wide the electro-magnet will not be able to act across it. Your manual should give you a recommended gap figure which you should check. Such adjustment is feasible with the water pump in the car. But the radiator really needs to be removed for accurate work and once this has been done you may choose to remove the water pump and carry out the adjustment on the workbench. There are different methods of adjusting the clearance. The Simca system employs three adjuster screws which run through both parts and are locked by lock nuts. To adjust the clearance, turn the screws each by exactly the same amount. The
VW Golf Mk 1 and
Passat employed a similar adjustable screw system.
An alternative design employed shims between the bearings and lock nut of the fan assembly. This lock nut should be removed, which will allow the fan assembly to be removed from the water pump spindle. Then, by using a variety of shims, you should replace the fan assembly the correct distance from the pulley. Another possible source of failure lies in the winding of the electro-magnet itself in the back of the pulley. The winding can break down and short circuit. To check this properly requires knowledge of the winding current through the coil. But a check of a total short can be made with the pulley in place. Temporarily connect the live terminal of the battery to the brush and connect an ammeter between the pulley and earth. This will indicate the winding current. If it shows zero or a low reading, there is a fracture in the wiring. A high reading will indicate a short-circuit somewhere in the unit.
The final area to check for trouble is the temperature-sensitive switch itself. If you suspect it is faulty then remove it from the radiator by unscrewing it. Next connect its terminals to a battery and a 12-volt bulb and place it in water. Heat the water and then measure the temperature at which the bulb lights. Your manual may give the specific temperature at which it should operate. If not, then you should expect it to work at just below 100 degrees Centigrade (212 degrees Fahrenheit).
Servicing an Electric Fan
The most sophisticated form of cooling fan on a water-cooled engine is the electric fan, controlled by a thermo-statically-operated switch, but free from any form of belt drive. This type of fan is basically just an electric motor switched on and off by water heat, with fan blades on the motor shaft. It can be mounted either behind the radiator to draw the air through or in front of it to blow it through. If the fan has failed then the first step is to decide whether the trouble lies with the fan itself or with the switch unit. The switch is generally located at the base of the radiator, either screwed in or clipped in place. Pull off the two wires which plug into the switch and touch them together. If the fan operates then the switch is faulty. The switch can be tested as above, but usually it either works or it does not. An electro-magnetic fan can also be tested this way.
If the fan does not turn with the switch shorted out, first check the wiring between the battery and fan by connecting the fan directly to the battery. If the fan still fails to turn, it indicates that the fault is in the fan motor. The electric motor will be held firmly in a frame and shrouded by a cowl. You should first disconnect the battery then remove as much of the covering as necessary to remove the electric motor. The motor will be held to its mounting frame by small bolts or self-tapping screws. Whether the radiator has to be removed or not will depend entirely on the model of car being worked on, but it may be necessary to do this before the fan and frame can be freed. This is especially true of the "blower" type fan which sits in front of the radiator. The fan, a light, nylon, pre-formed unit, is removed from the shaft by undoing a small bolt or screw to leave the motor free for servicing.
Unfortunately, from the home mechanic's point of view, many fans which are fitted to cars today are complete units and cannot be serviced. So before dismantling the unit, check the availability of replacement parts. If parts are available, to dismantle the motor proceed as follows. The motor is held together by long through-bolts. Remove these and the front end cover will come free from the body of the motor. The armature and brush gear will come out attached to the end cap. At this point you may notice the most common fault with electric : motors-worn brushes. These spring-loaded pieces of carbon are the link between the wiring and the motor and pass current to the commutator, which they should touch. If they are worn, it may be possible to replace them without further dismantling, but check first what form the replacements take.
On some British Leyland,
Fiat,
Alfa Romeo and
BMW cars the brushes are replaced as a complete assembly on their carrier and the armature must be removed from the end plate so that this can be taken off its shaft. The armature shaft will be held to the cover by a circlip and spaced by shims, which must not be lost. While the motor is apart, clean the commutator with a petrol-moistened cloth. If it is burned from contact with worn brushes, refinish it lightly with fine glass paper. A good guide for brush wear is that they should have a minimum length of about 5 mm (3/16ins). When re-building the motor make sure that all the shims and washers are properly in place and that any guide pegs and slots between cover and plate are lined up.
Finally when re-connecting the wiring make sure that you get it the right way round or the fan will suck instead of blowing or vice versa. There will be an arrow on the blades to indicate direction of rotation. If the fan rotates the wrong way, reverse the wiring. Once you have completed the service on any type of fan it is advisable to check that it is operating properly before embarking on any journeys. Driving the car around the block a few times should soon get the engine up to normal operating temperature, which is when the fan must really start its work of cooling the hot water flowing into the radiator. If the water temperature gauge still rises or the car shows other signs of overheating, the engine should be stopped and the fault rectified.
