MACS Service Reports - 2016 - JUL1

Total Vehicle Climate and Thermal ManagementTM

July 2016

By Dave Hobbs, MACS Technical Correspondent

ECT Sensor Diagnostics & Thermostat Monitors
It seems most everything under the hood is changing these days including how we approach thermostat diagnostics. Thermostats themselves have
changed little over the years with the exception of
the more recent addition of an electric heater to help
control the expansion of the wax and aluminum inside the stat that expands to move the valve to control the flow of coolant. While many engines have
adapted electric coolant pumps to replace the traditional belt driven water pumps, thermostats still
allow the coolant to flow from the block to the head
and heater core when closed and then to the radiator for heat rejection when open. They still are essential for pressure and flow control attributes that
assist the coolant in removing heat from the engine
hence the importance of the stat's presence even
when open. The correct thermostat temperature has
always been responsible for the right compromise
of engine performance and longevity. This usually
means starting to open around 110 deg. F and fully
open by the 180-195 deg. F rating of the stat. Auto
makers and technicians who service HVAC systems
have known for years that the cooling system is
there for more than just providing a source of heat
for the passengers and a means to prevent major
mechanical damage from the engine's combustion
events. Thermostats have helped to regulate cooling
system temperatures to get the right compromise of
higher temps for heater core warm ups / performance, emissions efficiency, and proper fuel atomization (ideally around 230 deg. F) while at the same
time avoiding temperatures that run high enough
to cause the production of NOx and engine damage.

The addition of pressurized systems that raise the
boiling point of water along with antifreeze with
a higher boiling point have all contributed to the
best compromise possible regarding cooling system
temperatures. So regardless of what type of performance you consider (fuel economy, power, emissions, longevity, etc.) we know that performance is
very dependent on proper engine cooling.

Thermostat Monitors
Thermostat monitors have been a mainstay of
OBD II emissions strategies for many years now.
The Malfunction Indicator light has been at times
renamed the MIL, a "Money Indicator Light" by
techs who have mastered OBD II diagnostics and
a "Misery Indicator Light" by techs who struggle
with the subject. It's not really that hard if you master the fundamentals; now, where to look for useful
information and the right tools for the job?

OBD II in a Nutshell
An OBD II monitor is simply a test. There are
many monitors (a.k.a. tests) the ECM / PCM runs.
Each of them is designed to catch an engine management system / component (catalytic converter,
ERG valve, sensors, actuators, etc.) failure which
could cause the emissions to exceed 1.5 times the
FTP limit (Federal Test Procedure). The ECM knows
what to look for with each test. For example, when
an ECM runs a portion of the EVAP monitor that
checks the ability of the charcoal canister to store
fuel vapors, it turns the purge solenoid off and on
while paying close attention to the O2 sensor. Nor

ALSO INSIDE THIS ISSUE:
Anatomy of an ECT Sensor / Sensor Common Woes .................................................................................................... 4

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Mobile Air Conditioning Society Worldwide, Inc., P.O. Box 88,
Lansdale, PA 19446. The material published in MACS Service
Reports expresses the views of the contributors and not necessarily that of MACS. Every attempt has been made to ensure

July 2016

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however, will not be responsible for the accuracy of the information published nor will MACS Worldwide be liable in any way for
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