Porsche 928 S 1986 Driver Manual page 64

To guard against corrosion, the mixture
strength of the cooling fluid should not be al-
tered, so even in warm weather, never top
up the system with just water.
The system should only be topped up with a
mixture of soft water and cooling system addi-
tive. For mixing ratios see the chapter "Filling
capacities".
To avoid damaging the engine, cold fluid
should only be added to a cold engine.
Note: There should seldom be need to top up
this sealed cooling system. If there is a con-
siderable fluid loss, it probably means a leak
in the system. This should be checked imme-
diately by an authorized dealer.
60
Draining and refilling the cooling system
1. With the engine cool, set the heating
lever to 30° C (86° F) and switch on the
ignition. Remove the cap from the expan-
sion tank.
2. Remove the drain plug from the radiator,
and catch the fluid.
3. Remove the two drain screws located left
and right in the engine and catch the fluid.
4. Renew the sealing washers on the drain
plug for the radiator and the two engine
drain screws, and refit.
5. With the engine stationary, refill the system
as full as possible.
6. Run the engine until it reaches normal oper-
ating temperature, checking the fluid level
constantly. If necessary, top up the level in
the expansion tank to above the middle line.
7. Refit cap to expansion tank.