maybe your thermostat is stuck open....or it is removed?? my gauge reads about 1/2 between cold and hot. I would assume 1/4 - 1/2 would be normal, but anything under 1/4 might be too cold. not sure though, maybe somebody who is certain can post on this.

another thing I just thought of is maybe the unit you replaced has too broad of a temp range. if stock range is, lets say 0 - 300 degrees and you replaced it with one that goes to 400 degrees, the gauge would read lower (colder) but if it were on the 300 degree gauge it might read in the middle.

 

Ya just like PUTG said, your T-stat is most likely stuck open. A couple months back my gauge was hovering around the quarter mark and it was taking forever to warm up....changed the T-stat and it brought it up to exactly half. I initially bought a cheapy one but then wanted this to be a done deal so took the other one back and went to Toyota and spend the extra $$$ and my baby loved it!

 

normal is about 1/3 scale.

Of course this varies some from truck to truck.

I think that first thing you would want to check is what temperature your engine is operating at. You can take the radiator cap off and check the coolant temp in the upper rad tank. It should be between 190deg F and 205deg F, if it is lower then try a thermostat.

another thing you can check while you have the cap off is watch the coolant in the upper tank you should not have apparent flow until the engine reaches operating temperature. Start with the engine cold and observe the temperature in the top tank of the radiator, it should only warm up slightly before the engine reaches operating temp

If the radiator warms up steadily or there is obviously a lot of flow before the engine gets to 180deg F or so then the thermostat is open too soon.