Thread: There was a question about a roar from a 300tdi

it will yes.

at speed, when the cooling system is worked up and the coolant is flowing its pulling heat from the metal of the block at rate X and the viscus hub gets itself into a state of equilibrium.

when you back off and slow down you loose airflow through the radiator, engine bay and slow down the flow of coolant so you get more heat transfer to the coolant because you still have the amount of heat in the block. This raises the temp of the coolant AND then slows the airflow through the radiator which in turn raises the air temp which quickly warms up the hub of the fan causing it to stiffen up which increases the drive to the fan which then pulls more air through the radiator which...........

from my MK I's on the puma the radiator appeared smaller in size but thicker in cross section than the tdi's

it will yes?

is that in anwser to my should my disco be roaring when coming off the freeway?

if so I will be buying a new clutch on monday

that was an answer to why the fan roars.

should your disco do it? thats a depends answer. theres a lot of variables. (plus the shrouding on a tdi appears less prone to amplifying fan noise than the puma one)


aircon on or off?
speed?
engine braking prior to slowing down (engine braking cuts the heat load because no fuel is going in but theres still plenty of movement of everything involved)
change in wind direction/speed
time of day/temperature?
were you travelling as fast? in close traffic or open?

my guestimate is that the disco will do it but less often than the puma.

Id do the standard paint brush when cold/hot test and if it was ok by that and roaring on start up Id say no, the hub is fine.

Hey DB, I asked the original question.

As blknight said, yes the hub will lock after a freeway run, but does this create a roar sound from a tdi fan?

From the responses I got, I believe the tdi fan does not actually make a roaring noise when it is fully locked up. Whether that be at startup, on a hot day, or after a freeway run.

I know my old D1 V8 made a real roar at startup and when hot.
The viscous units from a tdi and V8 have different part numbers and I understand the fans are different also.
No doubt the puma parts are different as well, although all the viscous units operate on the same principle.

As mentioned, I now think the tdi viscous fan does not actually make a roaring sound under any circumstances even when operating correctly (but I do stand to be corrected if someone's does roar).

the noise level does change its not as pronounced as a td5 or v8 tho.