Lesson 3/Learning Event 1
Once the engine starts, check the reading on the oil pressure gage right away. If the oil pressure gage does not
show pressure immediately, stop the engine and determine the cause before going any farther. Operating the
engine without oil pressure will ruin it in just a short time.
When the engine is cold and is first started, the oil pressure will be high because the oil is thick and does not
flow easily. Then, as the engine and oil warm up, the oil gets thinner and the pressure gets lower. The normal
oil pressure for each engine is listed in the technical manuals for the particular vehicle and for the particular
type of oil being used. The oil pressure specifications listed always pertain to readings that are obtained with
the engine at operating temperature. Make notes of oil pressure readings that do not agree with the
specifications in the proper technical manual.
Do not be too hasty in deciding the cause of faults if the oil pressure reading is not correct. The lubrication
system may be all right and the gage could be at fault. Look for simple things first, such as a loose wire,
components not grounded properly, and missing nuts and bolts. Little things are the problem more often than
Particular attention should be paid to unusual operating noises when the engine is cold and first started, as this
is when they are most likely to occur. Most noises, especially engine knocks, are caused by excessive clearance
between parts that work together. As the engine warms up, parts expand, reducing operating clearances and
noises. Here are some of the noises that you are expected to recognize as being uncommon.
A piston (wrist) pin knock. Loose piston pins will generally knock louder when the engine is not operating
under a load. A piston pin knock is sometimes mistaken for a connecting rod knock although the pin knock is
not as loud. If it is possible to adjust the exhaust valve so that it stays open all the time, the pin knock will
double up so it makes twice the number of sounds.