Section 03 ENGINE SYSTEM
Subsection 03 (COOLING SYSTEM)
CIRCUIT
A closed loop cooling system is utilized on the
1503 4-TEC engines, which offers an efficient en-
gine cooling while keeping dirt and salt water out
of the cooling system. This system keeps the
temperature constant and prevents internal en-
gine corrosion.
A separate coolant expansion tank ensures that
enough engine coolant is in the circuit during any
operating condition.
The coolant flow comes from the coolant pump
impeller into the cylinder block. It goes around the
cylinders and straight up to the cylinder head. A
smaller quantity of engine coolant enters the cylin-
der block on the exhaust side for a better cool-
ing. In the cylinder head the water channels flow
around the exhaust and then the intake valves and
leave the engine through a large hose. From there
the coolant goes back to the coolant pump hous-
ing and depending on the engine temperature, it
flows through the thermostat directly back to the
coolant pump impeller, or it takes its way through
the ride plate which operates as a heat exchanger.
Engine coolant is also directed towards the oil
cooler (coolant type).
Coolant temperature sensor and bleed nipple are
located on the cylinder head.
1
F18E0XA
2
1. Bleed nipple
2. Coolant temperature sensor (CTS)
CAUTION:
Never modify cooling system ar-
rangement, otherwise serious engine damage
could occur.
COOLING SYSTEM LEAK TEST
WARNING
To avoid potential burns, do not remove the
expansion tank cap or loosen the ride plate
drain plug if the engine is hot.
Install the test cap (P/N 529 035 991).
529 035 991
NOTE:
It is not necessary to install a hose pincher
on overflow hose.
Connect the vacuum/pressure pump (P/N 529 021
800) to test cap and pressurize system through
coolant expansion tank to 90 kPa (13 PSI).
1
F18E25A
TYPICAL
1. Vacuum/pressure pump
Check all hoses, ride plate, engine and oil cooler
for coolant leaks. Spray a soap/water solution and
look for air bubbles.
Check the leak indicator hole if there is oil or
coolant. If so, refer to the
1503 4-TEC ENGINE
SHOP MANUAL
.
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