A missing thermostat may or may not affect the smog check. If you mention to
the smog technician your Chevy's thermostat is missing, he or she must fail
your vehicle on the basis that there has been an emissions tamper. The
thermostat is considered part of your truck's emissions system. If you don't
mention anything, and if your Chevy produces acceptable emissions during the
smog test it will pass the smog inspection with no problem. It's rare that a
vehicle produces high emissions because of a missing thermostat but if could
happen. The thermostat controls engine temperature. For the smog test, it is
important the thermostat keeps the engine running hot to ensure fuel is
thoroughly burned in the combustion chambers. A missing thermostat may, and
this is a very rare "may", cause the engine to operate at temperatures below
what is needed to produce the lowest possible emissions, specifically
hydrocarbons or HC. We recommend installing a thermostat prior to the smog
check.
posted by SmogTips Support
