Chrysler Repair: 06 chrysler pacifica: temp gauge, chrysler pacifica, temp gauge

Question
QUESTION: Hello,
My hot/cold gauge was fluctuating so I took it in and they said there was a leak/crack in my radiator and replaced it. 3 months later, its doing it again. I noticed it when I left the car on with the a/c blowing and after about 45 minutes, it went up close to the red area and then back down. I changed the oil and it has gone back as high, though still fluctuating.the mechanic said to bring it back because it could be a defected part (radiator)?

ANSWER: Hi Saane,
When you way fluctuating, what fraction of the gauge is the flucthation covering? It is normal for the needle to vary about 1/4 of the full range as the thermostat opens and closes. If it is staying above 3/4 scale and approaching full H then that is not normal. But variation between 1/2 and 3/4 would not be an issue. It may be that there is air trapped in the cooling system which if bled out will solve the problem. Let me know what the mechanic finds and does and if it still isn't normal then let me know and describe the action of the needle.
Roland

---------- FOLLOW-UP ----------

QUESTION: Hello,and thank you for your prompt response. The needle usually stays on the half mark and doesn't move from there; however just yesterday it fluctuated higher all the way to the line right before getting to the red area, then would fall about two lines down. I will follow up once the mechanic takes a look and I tell him to bleed out the air in the cooling system. Also, would it hurt if I add water (just water alone) in the coolant bottle? I have heard this is fine though my manual says I should mix it.thx!

Answer
There is no problem to add water, so long as you don't have to do that regularly which would be a sign of a leak in the system. Continuing to just add water will dilute the concentration of antifreeze which can then result in the system boiling at a lower and lower temp until it will boil at 212 degrees when all the antifreeze is gone from the system. Don't over fill the bottle either.  If you are regularly needing to refill to the proper mark, then there is something causing a loss of coolant.
Roland
PS Thank you for the rating and nomination.