MACS Monthly Newsletter - 2020 - DEC5

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There are seven specific operating modes for the coolant
flow control system. They are:
1. Low flow with a cold engine start. The electric
water pump operates just fast enough to circulate just
enough coolant through the two valve passages, so
the coolant provides accurate temperature signals to
the sensors. The simultaneous objective is to warm
up the engine as quickly as possible, so there's minimum flow around the combustion chambers.
2. The pump continues at low speed to enhance
engine warmup. But if the motorist has moved the
controls to provide cabin heating and/or defrosting,
the pump speed is adjusted to increase heat transfer
to improve heated coolant flow to the heater core.
Flow of heated coolant from the engine is augmented by flow of hot coolant through the turbocharger
cooler.
3. Cabin heating continues and is improved as the
main coolant valve turns to put the engine coolant
flow into full radiator bypass. The block valve allows
coolant flow through the head.
4. Cabin heating (with radiator bypass) continues
and the main coolant valve allows flow through the
engine and transmission oil heat exchangers, with
coolant return to the water pump.
5. This is basically an engine-demand cooling
mode. If the heater controls are still calling for heat,
both coolant control valves will be positioned so there
will be heat as well as engine and transmission oil
heating, if necessary. However, the main coolant
valve will open the bypass as appropriate, to circulate coolant through the radiator.
6. This is another engine demand cooling mode,
but if the engine and transmission oil get too hot and
need cooling, the main coolant control valve will regulate the bypass flow to direct cooler coolant through
the engine and transmission oil heat exchangers.
7. This is an engine-off mode, basically a continuation of the previous one but with the water pump
slowed down to continue cooling.

Figure 9: The right side of the 2.7-liter four-cylinder holds
the water pump as shown, and the external plumbing allows
coolant to flow over the engine to the dual control valve.
electronically selected according to cooling demand from the
engine or heating demand in the passenger cabin.
There's a dozen sensors in the system, most for coolant temperature (engine block, cylinder head, engine inlet, engine outlet, radiator outlet, heater core inlet, heater core outlet). There are
two for engine oil temperature, one for transmission oil temperature, and one position sensor for each of the coolant valves.
With all those sources of information, the engine computer has
the ability to control the electric water pump precisely and the
ability to operate a separate electric actuator for each of the two
flow control valves. This enables the computer to regulate the
flow of coolant through the head, block, radiator, heater and engine and transmission oil coolers.
Example: The 2.7-liter four-cylinder turbo has the exhaust
manifold integrated with the cylinder head. The coolant in the
manifold is heated by exhaust gas flow, and the coolant flows
to the engine (block and/or head), engine oil cooler, automatic
transmission oil heat exchanger or cabin heater core. Engine
warmup is speeded up and temperatures at specific locations
are closer to optimum.

The seven " modes " aren't some continuous sequence that
the cooling system goes through. Each one depends on ambient
and operating temperatures and vehicle load, and whether and
when the heater is called for. A system is likely to start at the first
mode on a cold start in cold weather and quickly proceed to No.
2. But if the heater is off, the system might quickly go to No. 6.
If your scan tool software reads all (or most) of the sensors,
you'll be able to tell-maybe. Turning heat on or off will (or
should) trigger some reactions at the valves. n

December 2020

MACS Service Reports

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MACS Monthly Newsletter - 2020

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