Engine runs cold in the winter

I have a 97 Rodeo 3.2L 5-speed. In the cold months, when I drive on the highway the engine never warms up, in fact, it gets colder according to the temperature gauge. And if I put the heat on, only cold air comes through. So far, I put tape over part of the grill, and that solved the problem. The temp gauge now reads normal and I have Heat!!! Is this normal, and have other peps had the same prob.

Thanks

I had problems like this with my Eclipse over the winter when it was like 15 below. I drove to work (10 min. drive) and it didn't warm up the whole way there but ran just fine and it normally only takes a block or 2 for the temp guage to read in the middle. Then the next day when I was trying to figure out the problem it warmed up real fast like it does normally spitting out heat and everything. I ended up replacing the thermostat and I haven't had a problem since. Make sure you check your coolant and everything but try the thermostat they don't cost much and they're pretty easy to replace.