TM 5-2420-230-24-2
Coolant Thermostat (008-013)
B3.9 and B5.9 Series Engines
Page 8-10
Section 8 - Cooling System - Group 08
CAUTION
Always use the correct thermostat, and never operate
the engine without a thermostat installed. The engine
can overheat if operated without a thermostat because
the path of least resistance for the coolant is through
the bypass to the pump inlet.
An incorrect or malfunctioning thermostat can cause the
engine to overheat or run too cold.
As described in the coolant discussion, jiggle pins vent air
during filling of the coolant system.
After the engine is vented and filled, the jiggle pins act as
check valves to block the flow of coolant through the open-
ing during engine operation.
L-1066