Iscosities; Checking Engine Oil Level; Engine Oil Filter - GMC 4000 Series Service Manual

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LUBRICATION
IMPORTANT: Non-detergent and other lower
quality engine oils are specifically not recom ­
mended.
BREAK-IN OILS AND ADDITIVES
The use of proprietary blends of supplement­
ary additives or concentrates such as engine oil
supplements, break-in oils, tune-up compounds,
friction reducing compounds, etc., is not recom ­
mended in lubricating oils of the diesel engines
in GMC Truck and Coach vehicles. For gasoline
engines, if greater stability or detergency is de­
sired to reduce varnish and sludge formations, and
minimize wear, a thoroughly tested and approved
concentrate is available from GMC Dealers.
VISCOSITIES
Atmospheric temperatures and severity of
service determine the viscosity grade of engine oil
to use. Viscosity numbers constitute a classifica­
tion of lubricants in term s of viscosity or fluidity,
but with no reference to any other characteristics
or properties.
GASOLINE ENGINES
As a guide to the selection of the proper grade
or viscosity of oil to be used in gasoline engines at
various atmospheric temperatures, refer to "Vis­
cosity Chart" (fig. 4).
VISCOSITY CHART
For cold w eather, select visc osity b a s e d on low est an ticip ate d tem perature.
For hot w eather, select viscosity b a se d on h ig h e st tem p erature expected d u r in g
the d a y .
Figure 4 — G asoline Engine O il Viscosity Chart
G M C S E R V I C E M A N U A L
DIESEL ENGINES
around use. Where cold weather starting isa p ro b -
lem, it is suggested that other starting aids, oil
and coolant system heaters, as well as proper fuel
selection will be helpful. For further assistance,
consult your authorized GMC Dealer.
S.A.E. 10, etc.), and the m ulti-viscosity oils(10W -
30, etc.), are not recommended, except as a last
resort. If used, they should be replaced withS.A.E.
30 as soon as possible.
MULTI-VISCOSITY TYPE ENGINE OILS
are not normally recommended. However, some
may be effectively used to facilitate starting when
prolonged exposure of the engine to temperatures
below freezing is unavoidable. Consult your sup­
plier regarding the performance characteristics of
this type of oil and obtain his assurance of ade­
quate lubrication before subjecting the engine to
heavy-duty service.
have the first oil change at 3,000 miles.
decreased, depending upon experience with specific
oils or the recommendations and used oil analyses
as furnished by the supplier. Such a procedure
would be helpful in establishing the most practical
oil change period for the particular service.
Make the check perferably after a day's run and
after engine has been stopped for a few minutes.
Remove dipstick, wipe clean with cloth, reinsert
and remove again. The upper mark on dipstick is
"FULL," the lower "ADD." Keep level as close as
possible to "FULL" mark without overfilling. Do
not operate with level below "ADD" mark.
right side and engine can be filled at right filler on
valve rocker cover after removing filler cap (fig.
5).
door behind passenger seat. On other models, dip­
stick and oil filler are accessible when hood is
raised.
T_4 5 5 ,
related to crankcase oil changing periods, the qual­
ity of oil used, or the severity of the trucks service.
S.A.E. 30 engine oil is recommended for year
Lower S.A.E. engine oil grades (S.A.E. 20,
Multi-Viscosity lubricating oils, as a group,
OIL CHANGE INTERVALS
It is recommended that new engines should
The drain interval may then be increased or

CHECKING ENGINE OIL LEVEL

Daily, or oftener if necessary, check oil level.
On gasoline and diesel engines dipstick is on
On steel cab models, accessibility is through

ENGINE OIL FILTER

Oil filter element changing periods are closely