Engine Cooling System; Cleanliness; Gaskets And O-Rings; Capscrews And Metric Parts - JLG sky trak mmv Service Manual

8.5.2

Cleanliness

Cleanliness is very important during engine repair. Con-
tamination of the engine during repair will reduce the life
of an engine. Thoroughly clean the engine and engine
compartment area before attempting to service or repair
the engine.
DO NOT steam clean the following parts:
• Electrical Components
• Wiring
• Injectors
• Fuel Pump
• Belts and Hoses
• Bearings
During reassembly and inspection, thoroughly clean all
parts, and, where present, remove burrs and scales.
8.5.3

Gaskets and O-rings

NEVER re-use a gasket or o-ring. Use new gaskets and
o-rings. Thoroughly clean sealing surfaces before install-
ing a new gasket or o-ring. ALWAYS install new flat-faced
o-rings when servicing hydraulic fittings.
Cover any open ports of high-precision components
(such as fuel system equipment) exposed by removal or
disassembly to help prevent the entry of foreign material.
8.5.4

Capscrews and Metric Parts

When replacing capscrews, ALWAYS use a capscrew of
the same size and strength as the capscrew being re-
placed. Incorrect capscrews can result in engine dam-
age. Return capscrews removed from the engine to their
original locations.
The Cummins 4BTA 3.9 engine uses parts that are of
metric dimensions. Metric capscrews are described, in
millimeters, in terms of major thread diameter, distance
between threads, and overall length.
Metric capscrew dimensions:
M8 x 1,25 - 25
Length, in millimeters
Distance between threads, in millimeters
Major thread diameter, in millimeters
Verify that the correct type of part is used at all times.
Model MMV Rev. 12/04
Engine: Cummins 4BTA 3.9
8.6

ENGINE COOLING SYSTEM

The engine cooling system is a closed, pressurized sys-
tem that consists of coolant passages in the engine, plus
the oil cooler, thermostat, water pump, engine block heat-
er, hoses, radiator and radiator overflow bottle. The en-
gine is cooled by the circulation of coolant through
passages in the cylinder block, engine head and radiator.
Circulation is by thermo-siphon action, assisted by an im-
peller-type water pump, driven by a fan belt from the
crankshaft pulley. The water pump bearings are pre-
packed with a special grease and DO NOT require ser-
vice. Replace a faulty water pump. General engine
cooling specifications and maintenance procedures are
listed in Section 2, General Information, Specifications
and Maintenance .
8.6.1

Radiator Pressure Cap

The cooling system is designed to use a radiator pres-
sure cap to help prevent the coolant from boiling. In addi-
tion, the pressure helps to eliminate the formation of
steam pockets within the engine and ensures coolant cir-
culation throughout all coolant passageways of the en-
gine. For a 210° F (99° C) system, use a 13 psi (90 kPa)
radiator cap. An incorrect or malfunctioning cap can re-
sult in the loss of coolant and a hot-running engine.
8.6.2

Thermostat Replacement

Before considering thermostat replacement, check the
coolant level, fan belt tension and dash panel tempera-
ture indicator. If the engine seems to take a long time to
warm up, the thermostat may be stuck in the open posi-
tion and requires replacement. If the engine runs hot,
check the temperature of the upper radiator hose. If the
hose is not hot, the thermostat may be stuck in the closed
position. If the engine has overheated, performance may
suffer, indicating other damage including a leaking cylin-
der head gasket, cracked cylinder head or block, and/or
other internal engine damage.
a. Thermostat Removal
1. Level the vehicle, ground the attachment, place the
travel select lever in NEUTRAL [N], engage the
neutral lock lever, engage the parking brake switch
and shut off the engine. Secure accident prevention
tags to the steering wheel and ignition switch (refer
to Section 1.5, Accident Prevention Tag Usage ).
8.7