Engine Maintenance
100
Bleeding Air from the Cooling
System
Jiggle pin thermostats are original equipment on
units that have TK486V25 engines. Jiggle pin
thermostats make it unnecessary to bleed the air
out of the engine block because they keep air from
being trapped in the engine block. Normally, all
but about 1.5 qt (1.4 liters) of coolant drain out of
the cooling system when it is drained. If
approximately half of the Cooling System
Capacity (see Specifications Chapter) seems to fill
the cooling system after it has been drained, air
has been trapped in the block. Bleed the air out of
the block using the following procedure:
NOTE: If an engine runs with air trapped in the
block, the engine may be damaged. The high
water temperature switch may not protect an
engine that has air trapped in the block, because
the high water temperature switch is designed to
protect an engine from overheating due to
failures in the cooling system.
1. Remove the plug from the front end of the
water pump below the thermostat housing as
shown in Figure 162.
2. Slowly pour the coolant into the system until
you see coolant at the plug fitting.
3. Reinstall the plug.
4. Pour coolant into the system until it appears to
be full.
5. Make sure that the amount of coolant that
goes back into the system is approximately
equal to the amount of coolant that came out
of the system.
6. Start the engine. Monitor the coolant
temperature with the unit engine coolant
temperature gauge, or by using a non-contact
thermometer pointed at the thermostat housing
in the location of the high water temperature
switch or sensor. When the temperature
reaches 150 F (66 C), shut the engine off for 2
minutes. This allows time for the thermostat to
heat soak and open fully, ensuring that any
remaining air will be purged out of the engine
block when the engine is restarted.
7. Restart the engine and run it in low speed.
Remove the cap from the expansion tank and
slowly pour coolant into expansion tank until
it is full, then reinstall the expansion tank cap.
8. Repeat steps 6 and 7 until the coolant level
stabilizes.
Engine Thermostat
For the best engine operation, use a 160 F (71 C)
thermostat year-round.
CAUTION: Do not start the engine
without bleeding the air out of the block.
1.
Plug
Figure 162: Remove Plug from Water Pump
1
