so i have a 3013 ford taurus SEL with 137,000 miles on it. good condition. always replace tires when needed, oil changes and any maintenance that ever happened to it i always am fast to fix it. but the other day my coolant reservoir cracked and was spraying out the fluids so i had ordered a new one and installed it the next day and put new coolant in it and what not. well when i’m driving it doesn’t seem to have problems but when i am idle or put it in park the temperature gauge goes up and then down and up and down gradually. when i’m driving it seems to be at normal temperature. so before i had replaced it and before it cracked i didn’t have problems with the temperature at all. replaced it and now it’s acting funky. i have no idea about cars and have been doing research but can’t seem to find the answer. could anyone help me out on this?