How Engine Coolant Flows in a Cooling System?

The major cycle and the minor cycle

There two cycles that the engine coolant flows in the cooling system, one is the major cycle, and the other is the minor cycle. The way that the coolant flows in is controlled by the thermostat.

The major cycle is the cycle that the coolant flows through the radiator at a high temperature. In this cycle, the thermostat is open, the water route is: the water pump→the water jacket in the cylinder block→the water jacket in the cylinder head→a hose to the radiator→the radiator→a hose to the water pump→the water pump.



The minor cycle is the cycle than the coolant flows NOT through the radiator at a low temperature. In this cycle, the thermostat is closed, the water route is: the water pump→the water jacket in the cylinder block→the water jacket in the cylinder head→a hose to the water pump→the water pump.



If there is a heating system in the car, there would be a third water cycle, the water route is: the water pump→the water jacket in the cylinder block→the water jacket in the cylinder head→a hose to the heater→the heater core→a hose to the water pump→the water pump.

Here is the flow chart of the coolant cycle:



In the picture above, the CTS(coolant temperature sensor) receives the water temperature signal and transmits it to the ECU, then the ECU could control the cooling fan with this signal. The reserve tank is used to store any released fluid emporarily. In some cars, the coolant flows through the intake manifold to heat the gas mixture.

How Engine Oil Flows in a Lubricating System?

We know that the oil way is composed of oil passages in the engine, an oil pump, an oil filter, an oil stainer and an oil pan. Then how oil flows in the passages?

The main oil way:

The oil is drew from the oil pan through the oil strainer to the oil pump, then passes the oil filter and enters the main oil gallery in the cylinder block. If the oil pressure is too high, the relief valve will be pushed open to allow the oil to flow back to the oil pan. If the oil filter is clogged by impurities, the oil will enter the main gallery through the bypass valve without filtered.



1-bypass valve 2-oil pump 3-oil strainer 4-oil pan 5-drain plug 6-relief valve 7-oil filter 8-main oil gallery 9-oil passages 10-crankshaft 11-OPS 12-oil pressure light

The oil way is divided into two roads in the main oil gallery.

Oilway to the crank mechanism

The oil from the main gallery arrives to the main bearings through the oil passages in the cylinder block, then reaches the connecting rod bearings throught oil passages in the crankshaft. At the same time, the rotating connecting rod bearings will dip into the oil pan, and splashing the oil to piston pins, cylinder walls, and piston rings. Then the oil flows back to the oil pan.

Oilway to the valve train

The oil from the main gallery arrives to the camshaft bearings through the oilway in the cylinder head, and then to rocker arms and vavles. Finally, it goes back to the oil pan, too.

Modern cars have a oil pressure switch(OPS), so there is a small oilway to the OPS.

The complete oil circuit is below: