The engine cooling system
has had its fair share
of nips and tucks over
the last few decades but the
principal behind it is a simple one
and stays the same – keeping
the engine within a certain
temperature range and providing
heating for cabin occupants.
Progress in cooling systems, as with
most vehicle systems these days, is
being pushed by emissions and
efficiency. Several tweaks
to age-old components
have played a part in the
modern vehicle being more
powerful, using less fuel
and having cleaner
emissions than its
We are a long way
from the days of air
cooling and now
fans and electric
water pumps to name
a few. With these
components come new
fault codes and new ways to diagnose cooling systems.
Why are there wires going to the thermostat?
Electronically-assisted thermostats have been around for decades
now and their operating principle is still very much the same
as their earlier, mechanical ancestors. The main drawcards of
electrical control over
the thermostat are
increased power and
In a perfect world the
process in a passenger
car occurs at about
110°C. With mechanical
thermostats a middle
ground must be struck
and their rated opening
temperature can open
much lower than 110°C
to allow a ‘buffer’ for
thermostats have the
advantage of being able
to offer a much higher
opening temperature. These thermostats can remain closed as
high as 110°C – at this point they will open unassisted as the wax
pellet melts, just the same as a regular thermostat. This creates
the ideal temperature environment for emissions and efficiency.
The computer uses preset maps and watches several parameters
– including engine load, vehicle and engine speed, coolant and
intake air temperature – to operate the heating element and
quickly open the thermostat further.
This offers a rapid increase in cooling and drops the engine below
The lower temperature is ideal for
making power, allowing ignition
timing to be advanced closer to
optimal without increasing knock.
For this reason, the heating element
is most often operated under highload
conditions to increase cooling.
The heating element will also be
operated, even at low load, if the
coolant temperature rises above
113°C to combat overheating.
The graph on this page – a
simulated map that controls the
thermostat heating element – shows
what the computer is thinking (pic 1).
The coolant temperature is lowered
as vehicle load and
Check its pulse!
fans to low/high
staged relays, we
now commonly see
vehicles with pulsewidth-modulated
cooling fans. Pulse
width modulation ticks
all the efficiency and
NVH (noise, vibrations,
harshness) boxes for
The benefits of precise fan-speed control are obvious but often
the speed range is not infinite. It is quite common to have preset
stages of fan operation, loosely evidenced by only a handful
of speeds being available when bi-directionally controlling fans
through a scan tool. Understand that engineers have worked
long and hard to perfect these speed stages to provide a balance
between effective cooling, energy efficiency and driver comfort.
Under certain conditions
a 64 per cent duty cycle
may be ideal for cooling
but 61 per cent may be
a better option due to
the noise and vibration
of a particular fan
With a 10.61 per
cent duty cycle (blue)
commanded by the
computer, this small
cooling fan draws only
300 milliamps (red)
For testing purposes,
if no scan tool bidirectional
available, the old theory of increasing load to get the fans on high
still holds true, so set the a/c to max and turn on as many loads
With a rise in commanded duty cycle to 38.55 per cent (blue), fan
current increases to 814 milliamps (red) (pic 3).
Go with the flow
The theory for going electric with water pumps seems logical –
old mechanical-driven pumps, after all, rob precious power and
by Brendan Sorensen
The forecast is
hot for cooling
The Automotive Technician 9
Critical thinkers might
argue that you cannot
create or destroy
energy, so isn’t this
just putting more load
on the belt-driven
alternator to provide
power for an electric
Well, there’s a little
more to it than that.
pumps are directly
linked to engine speed,
so often pump more
coolant than is needed.
more coolant flow
would be ideal, such as during engine shut-off after hard driving.
The main benefit of an electric water pump comes from its
variable nature. Pulse width modulation allows the computer to
tailor fit the coolant flow to your engine’s current situation, and as
sparingly as possible. Electrification also provides several side
benefits, such as the reduced complexity of belt/chain designs
and the ability to remotely mount the pump in unused space.
Expect to see more of these modern water pumps because they
are ideal for hybrid and electric vehicles, which don’t have the
luxury of a constantly spinning mechanical engine.
Where to from here?
If you think we’ve made progress in cooling systems, grab an iced
tea because the future is hot.
The latest semi-conductors
used in hybrid and electric
vehicles produce a heat
flux measurement of
400W/cm², comparable to
the surface of the sun!
Huge cooling requirements
will be demanded from
stationary vehicles and
SAE J1772 electric-vehicle
allow for up to 240kW of
The sensitivity of
electronics creates the
need for very precise
cooling and this is where
glycol-coolant-based cooling systems show their age. Complex
systems with handfuls of small passages become hard to bleed
and regulate. The various metal components that require cooling
create bi-metal corrosion issues.
We are starting to see new solutions. The BMW i3 is an electric
vehicle that uses the existing a/c system to cool the battery pack
through refrigerant tubes mounted in a cooling plate, which acts a
But while the technology is changing the customer complaints will
remain the same. When Mrs Jones complains that her feet are
cold on morning drives, the keen technician will complement their
old-school physical tests and inspection with the interrogation of
data from all modules.
The poorly trained will quote a pair of slippers.