Thread: Guages

Originally Posted by Raptor05121

Yes there is. When you start an engine, the fuel and ignition system is in whats called "open loop". Basically, it dumps fuel into the engine to quickly get it to operating temperature. They are more efficient when at a specfic range. For our trucks, 195*F is the sweet spot. When you reach that temp, the system goes into "closed loop" which is an economy mode. If you never reach operating temperature, you are wasting fuel.

As I drive it slowly goes back up to normal I think for now I will be ok it doesn't stay down when I drive ... As I drive it goes back to the letters on my guage that say normal

Originally Posted by 5pointSlo

Technically you are only half right.... Open loop is to heat up the catalyst, not the engine. It will still go into closed loop (reading and using o2 sensors) even without a thermostat.... The reason your fuel economy decreases with a stuck open thermostat is because the engine cannot efficiently burn the fuel injected into the cylinder at low temperatures.

Well said