4 ms·

A thermostat in the context of an internal combustion engine is a coolant flow control device. It typically diverts coolant to the radiator when the engine init

A thermostat in the context of an internal combustion engine is a coolant flow control device. It typically diverts coolant to the radiator when the engine initially reaches operating temperature and then directs flow to manage ideal operating temps.

JorgeGT 7y ago
I know this, it's a pretty standard function that almost all cars have, and does not constitute a defeat device per se. It's also active all the time, that's how your car displays the coolant temp. in your dashboard. They should really explain how Daimler used this to cheat.
- rootsudo 7y ago
  Depending on how cooled the engine is, it affects emissions levels. A open thermostat makes a car run richer, generating less horsepower. There is a direct correlation between engine operating temp, condition of the thermostat and emissions/fuel economy.
  - korethr 7y ago
    > Depending on how cooled the engine is, it affects emissions levels. A open thermostat makes a car run richer, generating less horsepower. This is true on gasoline engines, which are homogeneous-charge, air-throttled designs, and target an operating point as close to stoichimetric as possible. Diesel engines are fuel-throttled, and by design run well lean of peak-EGT, stoichimetric, and even peak power due to their stratified-charge nature (overall stoich is rich-as-fuck at the combustion site). A diesel will blowing black smoke and melting holes in its pistons before it ever comes close to stoich, much less rich. A (relatively) richer running diesel engine will be making more power, not less. A diesel running cold with an open thermostat won't necessarily have it's fuel ratios affected so much as its injection timing. Injection timing absolutely does have an effect on emissions and fuel economy at any one given fueling/power-output level.

4 ms·

A thermostat in the context of an internal combustion engine is a coolant flow control device. It typically diverts coolant to the radiator when the engine init

by ewhanley 7y ago

JorgeGT 7y ago
I know this, it's a pretty standard function that almost all cars have, and does not constitute a defeat device per se. It's also active all the time, that's how your car displays the coolant temp. in your dashboard. They should really explain how Daimler used this to cheat.
- rootsudo 7y ago
  Depending on how cooled the engine is, it affects emissions levels. A open thermostat makes a car run richer, generating less horsepower. There is a direct correlation between engine operating temp, condition of the thermostat and emissions/fuel economy.
  - korethr 7y ago
    > Depending on how cooled the engine is, it affects emissions levels. A open thermostat makes a car run richer, generating less horsepower. This is true on gasoline engines, which are homogeneous-charge, air-throttled designs, and target an operating point as close to stoichimetric as possible. Diesel engines are fuel-throttled, and by design run well lean of peak-EGT, stoichimetric, and even peak power due to their stratified-charge nature (overall stoich is rich-as-fuck at the combustion site). A diesel will blowing black smoke and melting holes in its pistons before it ever comes close to stoich, much less rich. A (relatively) richer running diesel engine will be making more power, not less. A diesel running cold with an open thermostat won't necessarily have it's fuel ratios affected so much as its injection timing. Injection timing absolutely does have an effect on emissions and fuel economy at any one given fueling/power-output level.