92 Classic 3.9 overheats randomly

[Dantelaterra]

I have an odd issue with my 92 classic 3.9..... My Range is overheating now that it is hot outside. However it doesn't overheat every time that I drive, but I drive for an extended period of time then it overheats. I am going to replace the Thermostat and flush the radiator, but does anyone know what else it could be? I really don't think this is going to work. Last time I flushed the Radiator it seemed to work better and stopped overheating but now it's back to overheating only it is entirely random, the engine doesn't go into the red though, it runs just below the red on the temp gauge which makes me think that the water pump is working but something happens which causes the engine to run very hot, any ideas are appreciated, the first time it over heated I could hear the oil bubbling which I thought was really odd. After that I flushed the RAD and never overheated, just ran hot occasionally....

[Jerry 92RR]

Pull off the rubber strip between the rad and a/c condensor. Look in the narrow slot for debris i.e., leaves, lots of bugs.

Your fan clutch may also be failing/failed. Look for patterns in driving to duplicate the problem; are you driving in stop and go or at hwy speeds?

[jgkmmoore]

You have air in your heater lines that causes the bubbling sounds.
Heater on high heat and high fan, engine at operating temp. Open each cap CAREFULLY with engine running if temp is sane.
Make sure the surge tank cap seal is good.
Be sure the water is tapped up(engine off) thru the filler over the right/psgr side cylinder head. That air must be removed. Each time it gets to the pump, the pump will cavitate and just suck air instead of pumping. Common prob on the Classics. Fire it up, run for 2 minutes, shut it down and check filler again. May take 2-4 attempts to get it air free. Once you get the air out, you are 'Golden', and good to go(usually). DO NOT run your aluminum engine into the RED/HOT zone EVER. Cool is LIFE to those engines, and if you ignore this warning, you will pay dearly. Be sure your water hoses are in STELLAR condition...they are the lifeblood of the engine. Inspect the large LOWER radiator hose for sure. If it blows@ 70 mph, you are toast before you see the white smoke from under the car. Ask me how I know.........
Have you checked no water in oil and vice versa?
Rather than 'flushing' your radiator, take to a radiator shop and have them rod it out/clean it good. You can't tell if your radiator flow is correct from 'flushing', or just watching it. Using todays 'Radiator Flush' is tough on older radiators.

[Dantelaterra]

I bet there is air in the system, that must be what it is. I have found that around town driving below 55mph I never run hot and everything runs perfectly, but on the highway doing over 55mph it seems to start to run hot after some time.

I'm about to take it to an A/C repair place and I might have them get the air out of the system aswell, the place I am going specializes in A/C and Radiator repair