Hi, my 4.6 has just started to overheat in traffic, there is no fluid loss so I was thinking it may be the viscous fan. The temp is ok when on the move. Would anyone know how I could test it (without loosing any fingers!) before I go to the expense of changing it. Any advice on the fitting would also be good. Thanks, Paul
rewmer
Well-Known Member
The 4.6 has a small rad for a big engine, so any weakness in the cooling system will result in raised tempretures, which as we all know, is bad news for these engines. Personaly I would change the unit as a matter of course, dont take any chances. Also think about a new rad - yes I know its a big expence, but warped heads etc are even more.
Turn the engine off and wait for it to cool down.
If the fan is not faulty then it should spin freely with just a push of your hand.
When the temp rises with the engine running fluid flows from the vanes and locks up the fan causing it to spin at the same speed as the engine therfore cooling the engine down.
Generally these fans will fail in the locked position meaning that they run all the time overcooling the engine.
If your fan is not locked hen you should suspect something else.
If the fan is not faulty then it should spin freely with just a push of your hand.
When the temp rises with the engine running fluid flows from the vanes and locks up the fan causing it to spin at the same speed as the engine therfore cooling the engine down.
Generally these fans will fail in the locked position meaning that they run all the time overcooling the engine.
If your fan is not locked hen you should suspect something else.
ramon.alban
New Member
Hello Paul,
I believe the viscous unit referred to is similar to the item fitted to earlier Rover SD1 Efi cars.
In my experience the most common of two fail conditions is when the fan does not speed up due to insufficient bond between the wheel and the housing resulting in overheating especially in slow traffic, urban driving, towing or running air-con.
Lightly loaded at normal driving speed there is sufficient air passing through the radiator to cool the engine.
There are three reasons for such failure. Faulty bimetal coil, oil control shaft/valve siezed, or loss of oil.
A simple check is to press a rolled newspaper against the fan blades when a HOT engine is idling. If the fan can be slowed or stopped it is probably faulty.
A second and less common fail condition when the fan becomes permanently locked is potentially very serious.
Because the internal grooves are thin they can break due to age, internal corrosion, vibration, etc, with debris jamming between wheel and housing resulting in an over speed fan. Also, the oil control valve can sometimes jam in the open position allowing too too much fluid into the housing.
The air roars loudly and continously, more so at high engine speeds and such a condition may result in a thrown fan blade, resulting in severe imbalance and further breakage. If this happens broken parts are projected forwards into the radiator.
Never drive a car with a locked-up viscous fan.
For a much fuller explanation of how the normal Rover Efi Viscous fan unit behaves go to this link:
Rover SD1 Efi Viscous Fan Coupling
Ramon
Vintage Model Airplane and Rover SD1 3500cc Twin Plenum Vitesse
I believe the viscous unit referred to is similar to the item fitted to earlier Rover SD1 Efi cars.
In my experience the most common of two fail conditions is when the fan does not speed up due to insufficient bond between the wheel and the housing resulting in overheating especially in slow traffic, urban driving, towing or running air-con.
Lightly loaded at normal driving speed there is sufficient air passing through the radiator to cool the engine.
There are three reasons for such failure. Faulty bimetal coil, oil control shaft/valve siezed, or loss of oil.
A simple check is to press a rolled newspaper against the fan blades when a HOT engine is idling. If the fan can be slowed or stopped it is probably faulty.
A second and less common fail condition when the fan becomes permanently locked is potentially very serious.
Because the internal grooves are thin they can break due to age, internal corrosion, vibration, etc, with debris jamming between wheel and housing resulting in an over speed fan. Also, the oil control valve can sometimes jam in the open position allowing too too much fluid into the housing.
The air roars loudly and continously, more so at high engine speeds and such a condition may result in a thrown fan blade, resulting in severe imbalance and further breakage. If this happens broken parts are projected forwards into the radiator.
Never drive a car with a locked-up viscous fan.
For a much fuller explanation of how the normal Rover Efi Viscous fan unit behaves go to this link:
Rover SD1 Efi Viscous Fan Coupling
Ramon
Vintage Model Airplane and Rover SD1 3500cc Twin Plenum Vitesse
