the other day this little hatchback civic pulls up to me and starts revvin his engine so i look over and im like ok lets do this.. light turns green, i punch it, wheels are spinnin and surely i beat his lil punk a$$.. afterwards im drivin on the highway and i look at my temp gauge and the needle is only a quarter of the way up instead of the usual halfway.. i had a feelin it mite be the thermostat and just to make sure i asked a friend, who's a tech btw, and he told me the same thing.. my cousin tells me leave it this way cuz the colder ur engine runs the better.. now my question is, how bad is it for the engine if i keep it this way and is my cousin right.?? i know it's an easy job to replace it and fairly an inexpensive part cuz i've done it before on my old 95 max..

 

A cold engine will run to rich, possibly foul your plugs, build up excessive carbon deposits, ping, damage o2 sensors, consume to much fuel and lead to poor performance.

It should run at the temperature it's designed to run at so your fuel mixture burns correctly.