i have an aftermarket thermostat cap. it says 13psi.......i thought our stock one was rated from 14-18psi? today was a pretty warm and himud day and i noticed my temp guage climb to just under 3/4 of the way up. think that cap may cause this? going to go start my car with the cap of and turn the heater on and see if i can get any air bubbles out. coolant tank is full too.