MACS Service Reports - 2016 - AUG2

Electric Stats - The Advantage

throttle conditions are encountered. Because these
thermostats are PWM controlled, the duty cycle
output from the PCM to the stat can be controlled
with a variable signal that "averages" the position
of the thermostat opening when the engine load is
somewhere in between light and heavy throttle.

As mentioned in last month's MSR the thermostat
(purely mechanical or electric assisted) is still responsible for maintaining the engine's temperature
for the right compromise of engine performance,
heater performance, emissions, and engine longevity. A malfunctioning thermostat can go beyond the
usual overheating / underperforming heater core
extremes. It can lead to poor engine performance.
You don't have to have a drippy injector, ignition
misfire, faulty ECT or an excessive fuel pressure
problem to run rich. Rich fueling conditions can
happen when engine temps just don't get up to
where they should be. Wasted fuel can go beyond
the "wallet pain" at the pump to even greater financial pains when a catalytic converter experiences an
early demise due to sustained overly rich mixtures.
Superior fuel atomization for drivability occurs at
coolant temperatures in the neighborhood of 230
deg. F (110 deg. C) which in turn provides better
fuel economy and lower emissions. Engine coolant
temperatures lowered to around 194 deg. F (90 deg.
C) can provide for higher engine performance under heavy throttle due to the cooler (therefore denser) air being compressed into the cylinder when the
valves close.
The typical electric thermostat controlled by the
PCM can vary coolant temps in the 203 deg. F to 230
deg. F (95 deg. C to 110 deg. C) range during part
throttle conditions for those aforementioned lower
emissions / fuel economy improvements, then lower the cooling system temperature to the 185 deg. F
to 203 deg. F (85 deg. C to 95 deg. C) range when full

Electrical and Mechanical Explanations

Photos (left and center) courtesy GM
Drawing courtesy Audi

You may see a vehicle with an electronic thermostat and not even know it. The electrical connection
on them may resemble an ECT sensor. (Fig. 2) So
which type of stat does the vehicle you're working
on have - mechanical or electrical? A simple look
at the service manual for the vehicle's cooling system theory of operation or engine control schematic
should tell you what you need to know regarding
the type of thermostat in the cooling system. A
quick look into your favorite auto parts supplier 's
on-line catalog can also sometimes give you an indication to whether the stat is of the electrical variety
or purely mechanical. For example we looked at the
wholesale price of a Chevy Cruze electric thermostat and found prices ranging from $60-80 while a
similar vehicle's stat price that was purely mechanical ran between $15 and $30. That makes sense. As
with conventional non-electric thermostats, there is
still the principle of wax inside the sensing element
(thermocouple) of an electric thermostat along with
a spring and mechanical valve to control coolant
flow from the engine to the radiator. The big difference is the wax inside the mapped thermostat
can be heated up with an electric heater as well as

Figure 2: The electric thermostat functions as a normal thermostat with coolant temperatures rising thereby causing the wax compound to expand as heated and
begin the opening process. An electric heater warms up the wax quickly to open more quickly. This typically occurs under full load when engine temps can spike up.
Replacements typically are part of the gooseneck assembly.

August 2016

MACS Service Reports

Table of Contents for the Digital Edition of MACS Service Reports - 2016