Porsche 928 GTS 1994 Owner's Manual page 71

Engine oils
Use only engine oils which meet the specifica-
tions designated by Porsche. Your Porsche
dealer will be glad to advise you on the correct
type of oil for your engine.
These oils can be intermixed.
Since, however, each brand of oil has a special
composition, you should, if possible, use the
same oil brand if it becomes necessary to top
up between oil changes. Porsche engines have
long intervals between oil changes. You can
make best use of these long oil change intervals
72
by using multigrade oils or multigrade fuel effi-
cient oils since these are largely independent of
seasonal fluctuations in temperature.
If your vehicle is used in stop-and-go traffic in
winter, the engine will not always reach its op-
timum operating temperature.
from products of combustion may accumulate in
the oil. It is therefore advisable to change the oil
in spring so that your engine once again has a
100 % efficient engine oil.
Engine oil performance class
Engine oil is not only a lubricant, but also serves
to keep the engine clean, to neutralize the dirt
which penetrates into the engine through com-
bustion and to protect the engine against corro-
sion. To perform these functions, the oil con-
Look for
tains additives which
this label
developed for these functions.
So-called mineral oils are produced directly from
crude oil. The oils can be further refined (hy-
drocrack oils) or totally converted through a
number of chemical processes (synthetic oils).
These oils are structurally more efficient and re-
quire fewer additives than simple mineral oils.
Such oils are also known as non-conventional
oils.
The efficiency of an oil is expressed by classifi-
cations. The requirements for Porsche engines
are API class SG (US specification) and CCMC
G4/G5 (European specification).
Viscosity
Engine oil is viscous when cold, and thin-bodied
Condensation when warm. The viscosity of an oil is expressed
by its SAE class. For cold viscosity, the SAE
class is given as a number and the letter "W"
(as in winter); for hot viscosity, the SAE class is
given only as a number.
The viscosity of an oil is, therefore, always the
same for a specific temperature range if it has
the same number of an SAE class.
E.g.: A 10 W-30 oil and a 10 W-40 oil have the
same viscosity when cold; when hot the oil with
the number 30 is thinner than the oil with the
number 40.
have been specially
Single-grade/multigrade oils
Oils with two viscosities are called multi-grade
oils; oils with only one viscosity are termed
single-grade oils.
Single-grade oils can only be used for the nar-
row temperature range identified by their SAE
number; multigrade oils cover a wider tempera-
ture range (see chart).