MOTOR TRUCK SERVICE MANUAL
Engine Water Jacket
3. Gaskets must be in good condition to prevent
The water jacket permits coolant to be circulated
both internal and external leaks. If there are
around the cylinder walls, combustion chamber, and
external leaks around gaskets, there may also
valve assemblies. Some of these coolant passages are
be internal leaks into engine. Proper tightening
small and can easily become clogged if cooling system
of the head bolts with a torque wrench is
does not receive the proper maintenance. Figure 2
essential for preventing leaks around head
illustrates how rust and scale deposits will accumulate
inside the water jacket on an engine that has been
The water pump which circulates coolant through the
cooling system is likewise a most essential part. The
pump should be checked carefully for leaks and proper
lubrication, and if leaking, cracked or in bad condition, it
should be rebuilt or replaced promptly. For rebuild of
water pump, see Engine Section.
Fan and Belts
The fan should be checked for loose or bent blades.
A loose blade might work free during operation and
cause damage. A bent blade will reduce the fan's
Fan belts must be adjusted for proper tension. A
belt adjustment that is just tight enough to prevent
slipping on pulleys maybe considered a proper
adjustment. A tight belt adjustment is to be avoided
Fig. 2 Cross Section of Engine Shoving Cooling System
Thermostats used in H trucks are of the non-
adjustable-type and are incorporated in the cooling
system for the purpose of retarding or restricting the
circulation of coolant during engine warm-up.
Engine overheating and loss of coolant is some
times due to an inoperative thermostat. To check for this
condition, remove thermostat and test by submerging in
hot water and noting temperature at which thermostat
opens or closes. Use an accurate high temperature
thermometer for making this test.
Hose and Clamps
Hoses and their connections must be checked
regularly because they are often the source of hidden
trouble. Hose can oftentimes appear in good condition
on the outside while the inside will be partially
Fig. 3 Installing Core Plug Using SE1725 Installer Tool
deteriorated. If there are any doubts about a hose doing
with SE1581B Handle.
its job, replacement should be made. The clamps
should be inspected to make sure they are strong
1. Core plugs these are sometimes mistakenly
enough to hold a tight connection.
called freeze plugs.
They do not provide
protection against freezing expansion but are
only pre sent because of engine block casting
methods. Remove and replace core plugs that
show signs of leaking or rusting through Use
installing tool for core plug replacement (Fig. 3).
2. Drain plugs the water jacket of each engine has
one or more drain plugs. These should receive
seasonal care and kept free of rust and scale.