I Just bought a 98 vette 35K miles bought it last week, drove down the beach on Friday no problem. Saturday was in bumper to bumper beach traffic for say 20mins it over heated pulled over let it cool down brought it to the house 2 miles away saw fluid all over the radiator researve top on passinger side. let it cool saw no leaks anywhere, poured antifreeze started it up ran it temp got up to 170 idling fluid started to boil over out of the cap.

Today added more antifreeze let the cap off let it run for 20 mins Temp never got very warm, had the heater on as well, no issues. drove it can home 85miles temp gauge while driving (hwy 60-75mph) 72-84F when I stopped to pay tolls it got up to say 170-180 F got home turned about 3 mins later saw fluid leaking out of the cap again. I had the cap on as tight as I could.

Question:

why would it be leaking?
why would the temp show only 74-82F while on the hwy I know they ran alittle hotter than that?
the temp gauge fluxuates somtimes up into the 180-190s then down to 150 back down to 84, mostly stayed there the entire trip back.
I have a 2010 Saab one the motor is warm the gauge never moves constantly stays the same.


Im thinking thecap is bad cant hold pressure or Thremostat?
alos not sure why it overheated stop and go for only 20mins didnt have the air on

any help on this?

thanks