Chapter 5 Fundamentals of Engine Construction and Operation 87
service classification is SM for most gasoline engines and
CH4 for most diesel engines. Oils with other classifications
are only for use in older engines. However, older engines
can use engine oil with the newest classification.
In addition to the API grades, the International
Lubricants Standardization and Approval Committee
(ILSAC), made up of American and Japanese vehicle manu-
facturers, classifies oils according to manufacturer test
criteria. Classifications are called GF for gasoline fueled. At
the present time, GF-4 is the latest standard.
Oil Pan
Oil that drips or is squirted out of any part of the lubri-
cation system eventually drains into the oil pan. The oil pan
is a reservoir for engine oil and helps the oil to lose the heat
that it picked up in the engine. The air passing underneath
the vehicle removes this heat from the oil pan, Figure 5-25.
Most oil pans have a drain plug at the lowest point of the
pan. Some models have two drain plugs.
The oil pan is made of stamped sheet steel or cast alu-
minum. Aluminum pans may have cooling fins cast into the
bottom. The cast pan also adds some rigidity to the engine
block.
Some manufacturers are implementing a dry-sump
oiling system. In a dry-sump system, oil that reaches the
bottom of the pan is immediately pumped to a separate oil
reservoir. This leaves very little oil in the pan. The advan-
tage of this system is that it allows the engine to be set
lower, which allows a lower hood profile. Dry-sump oiling
is a proven system that has been used for many years in
auto racing and motorcycles.
Oil Pickup Screen
The oil pickup screen prevents any large particles,
such as dirt, sand, or metal shavings, from being circulated
in the lubrication system. The oil screen is installed on the
intake side of the oil pump, Figure 5-26. It is always located
at the lowest point in the oil pan. In this way, the screen is
always covered by oil. This keeps the oil pump from draw-
ing in air if the oil level drops because of oil consumption
or sloshing during turns or hard braking.
Since it traps only large particles, the oil screen usually
does not become plugged until the engine reaches very high
mileage. Most oil screens cannot be removed and cleaned
unless the oil pan is removed.
Figure 5-24. A—Oil containers carry an American Petroleum
Institute (API) marking indicating the oil viscosity and classifi-
cation. B—Oil temperature range chart.
Figure 5-25. The oil pan serves as the reservoir for the engine
oil as well as providing a surface for heat dissipation. Most
engines have a pan with a single sump. However, some engines
use either a dual- or dry-sump pan. (BMW)
Oil pan
Oil pump
Bottom of engine block
B
–
– – –
A
SM
Figure 5-26. The oil pickup screen is either bolted or pressed
onto the oil pump. The pickup reaches into the bottom of the oil
pan sump to draw oil into the engine. (Chrysler)
Intake
Oil
pump
Oil pickup screen
Bolt