This is a 2002 Mazda Millenia 2.5
I was drivng my car in very slow, stop and gottraffic with the AC on and my car started overheating. I pulled to the side of the road opened the hood and noticed that the fans were still running butthe enginewas still overheating. I turned the engine off and noticed that the radiator rubber hose was very stiff so after a while what I did was I opened the radiator cap (the one on the plastic tankwhereyou normallypoor antifreeze in) when when i did that it seemed like it releaved some pressure because it started blubbling and air came out. Also the rubber hose had no longer hadpressure and I was able to squeeze it. I put the cap back on and turned the car and the temperature was back to normal again. I drove unltil i got home and had no more problems.

My concern now is that I'm gonna make a 400 mile trip tomorrow and don't know if i should really use the car now that I had that problem eventhough it's no happening anymore. Is this something I should really worry about, is this a sign that something is broke and I need to fix it. please let me know cause i don't want to get stranded tomorrow.
Thank you

P.S. Also Ihad replace the thermostat for a newoneabout two years ago because it overheated and I was told that's what i had to replace.

 

sounds like the thermostat stuck. you can try changing it again, dunno if that will help. i would definetly try changing the radiator cap, and keep your old one just in case. if you do take the car on the trip, take at least a gallon of coolant mix. we have 2 99s', and both have had very similar situations. i have not yet changed thermostats, but i did change the radiator caps. although it has happened a couple of times, each time, i refilled the system, and it didnt happen again for a very long time. too long for me to suspect a faulty thermostat. you should learn to look at the gauges occasionally.

the cooling system is sealed. if you take the cap off when it is hot, you relieve the pressure. under pressure, the coolant mix has a higher boiling point. when you relieve the pressure, you lower the boiling point. when the system is cool, you can squeeze the radiator hose, and it will be kinda soft. when it is hot, the hose should be firm, that means it is holding pressure. if there is a leak, when you stop the car for a while, this is when the pressure will be the highest, and a leak will show itself. whenever the car has sat for a while and cooled down, you should always check underneath for liquid that has dripped. this is how i found out, my wife doesnt look at the gauges either. i also watch the temp gauge when the car is first started after it has cooled down, like overnight. this is when the thermostat is most likely to stick, and it will overheat. once it opens, you are usually ok.

 

I'm still having the same problem (engine heating up), it seems to come and go. It nappens once a whilein very slow traffic or waiting at the drivethrough. Once I get on to the highway it goes back to normal.Both fans work because i seen them kick in. What could be the problem, can it be the water pump and if is not how do i rule it out? how do i diagnose if it's the thermostat?
Thank you.

 

sounds like either the thermostat is stuck or the radiator is clogged up. if it is the thermostat, you don't have to be mechanically inclined to replace it.