Question: Will installing a lower temperature thermostat
help my engine run cooler and prevent it from overheating?
Answer: Yes, but it may cause more problems than it cures
if you have a late model vehicle. Before emission controls and
computerized engine controls came along, it was a common practice
to install a cooler (160 to 180 degree F.) thermostat for summer
driving. The lower thermostat lowered the engine's operating
temperature, which in turn reduced the load on the cooling system
and reduced the danger of overheating during hot weather driving
or when towing a trailer.
It was also common practice to again replace the thermostat
come fall and install one with a higher (190 to 195 degrees F.) temperature
rating. This would raise the engine's operating temperature so
the heater would put out more warm air on a cold winter morning.
This practice is no longer recommended because today's computerized
engine control systems require a constant year-round operating
temperature of about 195 degrees F.. The engine's emission controls
as well as it's fuel and spark control systems are all calibrated
to work within a given temperature range. If someone replaced
the thermostat with the wrong one for the application (either
colder or hotter), it can cause driveability, fuel economy, performance
and emissions problems. So if the thermostat is replaced for
any reason, it must be replaced with one that has the same (or
correct) temperature rating for your vehicle.
HOW TEMPERATURE AFFECTS ENGINE OPERATION
Coolant temperature is used for a variety of engine and emission
control functions. The coolant sensor on late model engines tells
the computer when the engine has reached normal operating temperature.
This, in turn, affects fuel enrichment, spark timing, operation
of the EGR valve, purging of the charcoal canister, etc. Even
on many non-computer engines, thermal vacuum switches (TVS) that
react to a specific coolant temperature are used to open and close
various vacuum circuits that regulate fuel enrichment, timing
and emissions.
If a colder thermostat is installed, the coolant may never
get hot enough to trigger the appropriate control functions in
the computer or TVS vacuum circuits. As a result the engine will
run as if it were continually cold, which increases both fuel
consumption and emissions. Too low an operating temperature also
increases cylinder wear.
CAUTION: Under no circumstances should an engine be driven
without a thermostat! This can produce thermal stress that may
crack a head or block!
What about a hotter thermostat? A hotter than normal thermostat
in a late model computer controlled engine may activate some control
functions too quickly or out of sequence with other control devices
(timer delays, etc.) --which could also have an adverse effect
on driveability, fuel economy, performance and emissions.
