STEM .................................................... 7-3
7.3 TH ER MO STAT ........................................................................................ 7-7
7.4 WAT ER PUMP ........................................................................................ 7-8
7.5 TYPES OF COOLING SYSTEMS ........................................................... 7-8
7.6 A IR-TO - AIR CHARG E CO OLING ........................................................... 7- 11
7.7 C OO LING SYST EM PERFO RMANCE REQUIREMENTS ..................... 7- 13
7.8 C HAR GE A IR C OO L ING R EQUIREMENTS .......................................... 7- 16
7.9 E ND PRO DUC T QUESTIO NNAIR E ....................................................... 7- 17
7.10 C OO L ING SYST EM D ES IG N CO NSIDERATIO NS ................................ 7- 17
7.11 C HAR GE AIR C OO LING D ESIG N GU ID EL INES ................................... 7- 24
7.12 H EAT EXCH AN GER S EL ECTIO N .......................................................... 7- 26
7.13 FA N SYSTEM RECO MM EN DAT IO NS AND FAN SE LECT IO N .............. 7- 27
7.14 R ADIATO R CO MPO NENT DESIG N ....................................................... 7- 34
7.15 D IAG NO STIC S A ND TRO UBLES HO OTING .......................................... 7- 53
7.16 M AINTENANCE ...................................................................................... 7- 57
All information subject to change without notice.
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7.1
COOLING SYSTEM DESCRIPTION
The MBE 4000 cooling system is comprised of two separate systems; the jacket water cooling
system and the Charge Air Cooling (CAC) system. Although these systems are separate, they
usually share the same space which makes each system's performance dependent upon the other.
A well designed cooling system is a requirement for satisfactory engine performance and
reliability. Thorough knowledge of the application, duty cycle, and environmental conditions is
essential in designing and packaging the total cooling system. A properly designed system should
still be able to perform within specifications after normal system degradation occurs.
The jacket water cooling system consists of a heat-exchanger or radiator, centrifugal type water
pump, oil cooler, thermostats, and cooling fan. The water pump is used to pressurize and circulate
the engine coolant. The engine coolant is drawn from the lower portion of the radiator through the
water pump and is forced through the oil cooler and into the cylinder block. The heat generated
by the engine is transferred from the cylinder and oil to the coolant. The heat in the coolant is
then transferred to the air by the cooling fan when it enters the radiator.
Two full blocking-type thermostats are used in the water outlet passage to control the flow of
coolant, providing fast engine warm-up and regulating coolant temperature.
The CAC system consists of the air inlet piping, the turbocharger, the cooling fan and the intake
manifold. Ambient air is drawn in through the air cleaner and piping to the exhaust driven
turbocharger. The turbo compresses the air which increases its temperature by about 300 F
(150 C). The charge air is then cooled by the air from the cooling fan as it passes through the
CAC to the intake manifold.
7.2
JACKET WATER COOLING SYSTEM
When the engine is at normal operating temperature, the coolant passes from the cylinder block
up through the cylinder head, through the thermostat housing and into the upper portion of the
radiator. The coolant then passes through a series of tubes where the coolant temperature is
lowered by the air flow created by the fan.
Upon starting a cold engine or when the coolant is below operating temperature, the closed
thermostats direct coolant flow from the thermostat housing through the bypass to the water
pump. Coolant is recirculated through the engine to aid engine warm-up. When the thermostat
opening temperature is reached, coolant flow is divided between the radiator inlet and the bypass.
When the thermostats are completely open, all of the coolant flow is to the radiator inlet.
The function of the engine coolant is to absorb the heat developed as a result of the combustion
process in the cylinders and from component parts such as the valves and pistons which are
surrounded by water jackets. In addition, the heat absorbed by the oil is also removed by the
engine coolant in the oil-to-water oil cooler.
The following illustrations show the coolant flow within the cooling system, when the thermostats
are closed (see Figure 7-1) and open (see Figure 7-2).
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Figure 7-1
Thermostats Closed
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Figure 7-2
Thermostats Open
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A pressurized cooling system permits higher temperature operation than a non-pressurized
system. It is essential that the cooling system is kept clean and leak-free, that the filler cap and
pressure relief mechanisms are properly installed and operate correctly, and that the coolant
level is properly maintained.
As the engine temperature increases, the coolant and air in the system starts to expand and build
pressure. The valve in the radiator pressure cap unseats and allows the trapped air to flow out
the overflow tube. See Figure 7-3.
Figure 7-3
Coolant Expansion
When the engine starts to cool down, the air and coolant contract, causing a void and creating a
vacuum in the system. The vacuum unseats another valve in the radiator pressure cap, allowing
the coolant to flow back into the radiator.
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7.3
THERMOSTAT
The temperature of the engine coolant is controlled by two blocking-type thermostats located
in a housing on the front of the cylinder head. See Figure 7-4.
1. Mounting Bolt
4. O-ring
2. Thermostat Housing
5. Thermostat
3. Upper Coolant Tube
8. Coolant Pump Housing
Figure 7-4
Thermostat and Related Parts
In addition to a rubber seal that is part of the thermostat, there is a lip-type seal for each thermostat
that is installed in a bore in the thermostat housing.
At coolant temperatures below the operating range the thermostat valves remain closed and block
the flow of coolant from the engine to the radiator.
During this period, all of the coolant in the system is recirculated through the engine and is
directed back to the suction side of the water pump via an internal bypass tube. As the coolant
temperature rises above the starttoopen temperature, the thermostat valves begin to open,
restricting the bypass system, and allowing a portion of the coolant to circulate through the
radiator. When the coolant temperature reaches an approximate fully open temperature, the
thermostat valves are fully open, the bypass system is blocked off, and the coolant is directed
through the radiator. Thermostat closing and opening temperatures are listed in the Technical
Data section of this manual (refer to section 14).
Properly operating thermostats are essential for efficient operation of the engine.
All information subject to change without notice.
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7.3.1
ENGINE VENTING
A single engine vent locaton is provided at the top of the EGR cooler. Vent lines from each
cylinder head are tied together with the EGR cooler vent. This is intended to be used to release
trapped air to the surge tank. This vent line should go to the top of the cooling system surge tank,
above the water line. The vent line must include a restriction of 4.5 mm diameter.
7.4
WATER PUMP
The centrifugal-type water pump circulates the engine coolant through the coolant system.
The pump is mounted on the front of the engine block and is belt driven by the crankshaft pulley.
7.5
TYPES OF COOLING SYSTEMS
Radiator cooling systems can be classified into two broad categories: rapid warm-up and
conventional. Only rapid warm-up systems are acceptable on the MBE 4000.
7.5.1
RAPID WARM-UP COOLING SYSTEM
The rapid warm-up cooling system eliminates coolant flow through the radiator core during
closed thermostat operation.
This reduces warm-up time and maintains coolant temperature near the thermostat start to open
value. Having the deaeration tank (internal or remote) separated from the radiator core will
accomplish this. External vent and fill lines as well as internal standpipe(s) (radiator core air vent)
are required in the deaeration tank. Proper size and location of these components are critical to
having a balanced system. The fill line coolant return flow capabilities must exceed the flow into
the tank under all operating modes. Positive water pump inlet pressure must be maintained in
all operating conditions. The rapid warm-up cooling system has also been called positemp,
continuous deaeration, or improved deaeration.
Another advantage of this system is its ability to place a positive head on the water pump, thus
reducing the possib