JLG G12-55A Service Manual - Manual (Page 108)

Engine
7-4 G10-55A, G12-55A
7.2 ENGINE COOLING SYSTEM
7.2.1 Surge Tank Cap
A 17.4 psi (1,2 Bar) cap is used on the surge tank. An
incorrect or malfunctioning cap can result in the loss of
coolant and a hot-running engine.
7.2.2 Thermostat Replacement
Before considering thermostat replacement, check the
coolant level, fan belt tension and instrument cluster
temperature indicator.
• If engine seems to take a long time to warm up,
thermostat may be stuck in open position and
requires replacement.
• If engine runs hot, check temperature of upper
radiator hose.
• If hose is not hot, thermostat may be stuck in
closed position.
• If engine has overheated, performance may
suffer, indicating other damage including a
leaking cylinder head gasket, cracked
cylinder head or block, and/or other internal
engine damage.
a. Thermostat Removal
1. Park machine on a firm, level surface, level machine,
fully retract boom, lower boom, place transmission
control lever in (N) NEUTRAL position, engage
parking brake, and shut engine OFF.
2. Place a Do Not Operate Tag on both the ignition key
switch and steering wheel.
3. Open engine cover. Allow system fluids to cool.
4. Properly disconnect the batteries.
5. Slowly turn surge tank cap and allow any pressure to
escape. Remove surge tank cap.
6. Place a funnel at the base of the radiator to channel
drained coolant into container. Loosen draincock
and slowly remove to allow the coolant to drain.
Transfer coolant into a properly labeled container.
Dispose of properly if coolant needs to be replaced.
Replace radiator draincock.
7. Loosen and remove the top radiator hose from the
thermostat housing.
8. Disconnect the engine water temperature sender (1)
if connected to the thermostat housing.
9. Remove the two capscrews (2) securing the
thermostat housing (3) to the engine.
10. Remove the thermostat housing, old gasket and
thermostat. Clean all gasket surfaces. DO NOT let
any debris into the thermostat opening.
Note: ALWAYS use the correct thermostat and install a
new gasket. NEVER operate the engine without a
thermostat, or engine damage will result.
b. Thermostat Installation
1. Install engine thermostat, thermostat gasket and
thermostat housing. Secure with two capscrews and
torque as required.
2. Connect the engine water temperature sender if
connected to the thermostat housing.
3. Properly connect the batteries.
4. Open surge tank cap, and fill system complete to the
“Full Cold” level with coolant. Replace and tighten
surge tank cap.
5. Run engine to operating temperature. Visually check
for leaks with engine running. Check coolant level in
surge tank and fill, or drain, as necessary.
6. Close and secure engine cover.
7. Remove the Do Not Operate Tags from both the
ignition key switch and the steering wheel.
MY4520
2
1
TYPICAL
THERMOSTAT
2
3