My 94 LS takes about 3 miles for the gauge to get to a bit left of center and then stay there. Its been about 0 in the morning and single digits in the afternoon. One thing that makes a little difference is to keep the fan off, or on very low until I see the gauge at least 1/4 the way. Your core is like another radiator taking heat out of the coolant. If its way beyond that, make sure the radiator is full, and see if bottom hose ever gets warm. Only thing that could really keep it from coming up to temp is an open stat.