93
Cooling system
General
The engine has two cooling circuits. The closed cir-
cuit is filled with coolant which is used for cooling
the cylinder block and cylinder head. This coolant is
also used to cool the exhaust manifold. The sea wa-
ter circuit uses sea water, which is drawn directly
from the outside of the boat, to cool the coolant in
the closed circuit and to cool the engine oil (only A-
engines).
The heat exchanger, exhaust manifold and coolant
tank for the coolant in the closed circuit are com-
bined in one unit. This is installed on the right of the
engine. On B-engines the oil cooler is also built into
the heat exchanger (MD22L-B has no oil cooler).
The coolant in the closed circuit passes from the
coolant tank to the intake side of the pump. From
the pump the coolant passes through the cylinder
block and cylinder head to the thermostat housing.
If the coolant is cold, it passes through the by-pass
connection directly to the intake side of the pump.
When the coolant temperature increases, the ther-
mostat valve opens, the by-pass connection closes
and the coolant passes through the heat exchanger.
In the heat exchanger the coolant passes along the
outside of the pipes and is cooled by the sea water
in the pipes. The coolant then leaves the heat ex-
changer and enters the tank unit, where it cools the
exhaust manifold which forms an integral part of the
unit. The coolant then moves to the intake side of
the water pump. Some of the coolant passes
through an outlet in the rear of the unit to an oil
cooler and then to the intake side of the pump (only
A-engines).
The sea water is circulated by the sea water pump
which is directly driven from the rear end of the
camshaft on A-engines and belt-driven from the rear
end of the camshaft on B-engines. From the pump
the sea water passes through the heat exchanger
pipes and is then expelled through the outlet.
Outline diagram MD22A, MD22L-A, TMD22A
4. Engine oil cooler
5. Freshwater pump
6. Sea water pump
7. Outlet bend
1. Cylinder block
2. Thermostat
3. The combined coolant tank, heat ex-
changer and exhaust manifold
To Next Page
Loading...
Need help?
General
