Miscellaneous Cooling System Checks
In addition to the above cleaning procedures, the other components of the cooling system should be checked periodically
to keep the engine operating at peak efficiency. The thermostat and the radiator pressure cap should be checked and
replaced, if found defective. The cooling system hoses should be inspected and any hose that feels abnormally hard or
soft should be replaced immediately.
Also, check the hose clamps to make sure they are tight. All external leaks should be corrected as soon as detected.
The fan belt must be adjusted to provide the proper tension, and the fan shroud must be tight against the radiator core to
prevent re-circulation of air which may lower cooling efficiency.
A centrifugal-type water pump is mounted on top of the engine oil cooler housing, either on the right-hand or left-hand
side of the engine, depending upon the engine model and rotation. It circulates the coolant through the cooling system.
The pump is belt driven, by either the camshaft or balance shaft (In-line engines) or by one of the camshafts (V-type
An impeller is pressed onto one end of the water pump shaft, and a water pump drive pulley is pressed onto the opposite
end. The pump shaft is supported on a sealed double-row combination radial and thrust ball bearing. Coolant is
prevented from creeping along the shaft toward the bearing by a seal. The shaft and-- bearing constitute an assembly
and are serviced as such, since the shaft serves as the inner race of the ball bearing.
The sealed water pump shaft ball bearing is filled with lubricant when assembled. No further lubrication is required.
Contact an authorized Detroit Diesel Allison Service Outlet if more information is needed.
Raw Water Pump
The raw water pump (Figs. 20 and 21) is a positive displacement pump, used for circulating raw water through the heat
exchanger to lower the temperature of the engine coolant. It is driven by a coupling from the end of the camshaft.
Seal failure is. readily noticed by a flow of water visible at the openings in the raw water pump housing, located between
the pump mounting flange and the inlet and outlet ports. These openings must remain open at all times.
Figure 20. Raw Water Pump Used on In-Line Engine
Figure 21. Raw Water Pump Used on V-Type Engine
The impeller, cam and wear plate assembly, and water seal assembly may be serviced without removing the pump from
the engine as outlined below.
1. Remove the cover and gasket.
2. Note the position of the impeller blades to aid in the reassembly. Then grasp a blade on each side of the impeller
with pliers and pull the impeller off of the shaft.
3. The neoprene spline seal(s) can be removed from the impeller by pushing a screw driver through the impeller from
the open end.