This morning my engine temperature light came on as soon as i started my 1990 gti(1.8). The same thing happened later in the day. The light just comes on and never goes off. Since the engine is cold i'm assuming it's a deffective thermostat. Could it have something to do with the fact that this morning it was -10 celcius(15 f) outside and last night it was 5 celcius (35 f). Any ideas?