Was just driving home on the highway after work last night (so, this happened at high speed), upstate NY, about 50 degrees. "Check Gauges" light came on, temp. meter was pegged "HOT!!". Pulled over ASAP, shut 'er down, waited a while, started up again. Tried to turn on the heater to help cool down, but only cold air was blowing in the cabin. Let it cool down, ran it again, "Low Coolant" light came on. Added water to the overflow reservoir with help from bystanders, was still overheating when running the car, completely cold air in cabin. Limped home, added coolant over a couple of cycles (thought it might be air burping problem - see previous problem described below), still overheats after cycling this way five or six times (I6 has no bleeder – manual says to cycle the coolant refill). Air in the cabin is still cold even when the temp gauge is pegged hot. No leaking from anywhere.

Other info: belt is OK, water pump is turning OK as far as I can tell with no weeping/grinding/squealing, upper hose is HOT, lower is not so hot. Heater line "in" to core is HOT, "return" not so hot. A few weeks back, my fan relay died after another overheating incident, replaced that and all fans function perfectly now. When I first bought it used about 6 years back, the water pump went, and I replaced the pump, t-stat, and hoses. Coolant is clean, I filled it with 50/50 mix with distilled water, never had a problem. Car has 120K miles and everything has been perfect up until now. All cooling system components are dead stock and in normal configuration.

Was thinking I lost some fluid during the last overheat due to the relay, and I might not have noticed that I cooked it off. Also might have lost more last night, so maybe that’s why the “low” indicator went off (sensor in overflow tank). So, maybe I was running a little low to start with...but, why the overheat now? Why cold air in the cabin only? Was running fine since the relay replacement about 4 weeks ago. Only thing I could think of was an air bubble being sucked in as a result of low coolant in the overflow tank, but cycling the coolant refill 5 times still hasn't done it. I even popped the sensor plug on the t-stat housing to see if any air seeped out - nothing but fluid. Maybe something as simple as a t-stat going bad?

I'm totally confused and am considering a whole cooling system overhaul - got no time to mess around right now. Before I do.....anyone have any other ideas for checks/tricks/solutions/similar incidents? Any help would be GREATLY appreciated!

Thanks!!

not sure this is related - but I did loose heating inside the cabin - it was a vacuum leak. On the canister under the front bumper the line came loose. Might be worth a look