Jeep Repair: Jeep runs cold after getting new water pump, jeep cherokee sport, water pump replacement

Question
QUESTION: What a wonderful forum!  I have a 1998 Jeep Cherokee Sport.  It has only 79,000 miles and has been a very reliable car (I'm the original owner).  The water pump went out a couple of months ago and, ever since then, the temperature gauge has shown that the jeep is running much colder than it used to.  The temp gauge is almost never in the 1/2 way range, but almost always around the 1/4 mark.   The car is running ok, but can it be good to run cold like that?  Most of my trips are fairly short (7-10 miles or less) and I seldom get on the freeway.   Thanks so much!

ANSWER: if there was a prob with the engine being to cold to long u would have a  check engine light on for that. U might have some air in the system after the water pump replacement.

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QUESTION: Thanks!  Is "air in the system" a problem?

Answer
trapped air in the system will change the reading on the sensor  its like if u have air will read different temp then water. U can bleed it out but u will need some help with it by loosing up the top rubber hose from the heater core and let some air out while the system is under pressure.