On my normal 25 mile commute to work, the temp never really fluctuates more that 2 degrees over 194. Last week on the trip down to NC to see the grandkids, the temp was fluctuating by 5 - 10 degrees, settling on 201 until the last 3 hours when it went back to 194 plus or minus.
The car sat for three days, then I left to go back to PA. I left at 0500, and as I was driving the back roads to get to the interstate, the temp kept climbing, and climbing,and finally the overtemp lite came on. I pulled over immediately, popped the hood, and found nothing, except that the coolant expansion tank looked like it was filled to the very top. No boiling over, no hissing, no smell of coolant. I banged on the expansion tank a few times, backed off on the cap, which somewhat relieved some pressure. Then I restarted the car and gingerly drove it as it warmed up. It settled on 199 - 201 for 8 of the ten hour ride, then it was back down in the customary (for me) 194 range.
I have done nothing to the cooling system since I bought the car. It's garaged always. I'm not really excited about draining and replacing the coolant, then jacking the left front up to get the air bubbles out, but I don't want to be stuck out on the road.
Did I experience an about to expire thermostat? or just a weird occurrence?
Thanks for any input/ideas,
Tailhooker