I was driving my truck with the air conditioner running and the check engine light came on. The temp gauge read 260 degrees. I turned the heater on full blast. The truck began to cool down a little. I noticed the heater was not getting hot. And the gauge was not going back to 220 it was staying at 240.when I got home we looked under hood. The top hose to radiator was hard and swollen and water was backing up in reserve and not running thru radiator. We replaced the radiator and didnt fix problem. Now the radiator fan and electric fan do not come on and top hose still gets hard and backwashes.

heater core or thermostat is failing.

The computer is supposed to ground the fan relay when the engine temp reaches 220 degrees. If the coolant level is low, or the sensor is faulty, the computer will not know the engine needs the fan.
A mechanic would check the sensor with a scanner or meter.
Its also possible the gauge on the dash is not accurate.

fans came late on those car,like 212 and second fan comes on at 224,you reprogram it to come a lot sooner,,other thing is there might be gunk inside the block,and coolant has hard time to pass through,and staying longer than enough in block temp goes high,even tough the radiator is doing it's job,it is just coming out block lot hotter than it suppose to be,and gauge read the block not the radiator

Make sure coolant is full & cooling fan working , no debri in. Radiator

The first hing I would do is confirm the engine temp with a scan tool. If the scan tool is reading a normal temp, 200 to 220 degrees with the fan coming on at around 220 degreese, and the gauge us reading much higher than the gauge is most likely bad. If the fans are not coming on than you need to look into that. Fuses, relays, wiring, fan motors would be the basic things to check. If you need more help with figuring out the fans let me know. If the fans are coming on, the temp gauge is reading the same as the scan tool data that there are a couple of possibilities. Either the system has air in it from nepot being properly bled or the headgket is bad forcing air into the system. Air will cause the cooling system to lock up. If you are try ing seeing the temp gauge spike to 260 degreese the head gasket is likely to have or will fail soon. Like I said if you have any further questions let me know and I'll be happy to help.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

jtg

you need to check fluid level in radiator,low coolant will cause your problem,but fill the resivour too,
you need to see if you lost fluid first,then check fan operation,

Have you checked the antifreeze level lately? Low antifreeze will cause a temp sensor to give false readings. Does your heater work OK, as in does it blow hot air when heater is on? that is another symptom of low antifreeze.

As far as the check engine light coming off and on, I would bet it is the oxygen sensor that might need to be replaced.

It sounds like your cooling fans are not comming on by themselves, but when you turn on the ac it forces them to turn on. Make sure relay is good, then replace coolant temp sensor, this may have failed no telling pcm to turn on cooling fans. Thanks

It sounds to me like you're low on coolant. When you checked the coolant level, did you actually open the radiator cap and make sure the radiator is full? The plastic tank you generally add coolant too is actually an 'overflow' or 'reserve' tank. There is a hose that runs from that tank to the top of the radiator so if the radiator gets low on coolant, more coolant -should- run in from the overflow tank. However in practice this does not always work. I have a Jeep that leaks coolant and experiences this exact same problem. Coolant will not run from the reserve tank into the radiator because the hose is plugged up, and whenever the radiator gets low on coolant the temp gauge will go real high and then drop, and the heater doesn't work well. This is because the cooling system of your car is supposed to be a closed system, full of coolant and no air. When coolant leaks out, the space it used to occupy is now occupied by air, which does not transfer heat well. When 'air' is passing through your cooling system, no heat can be transferred from your engine to the heater and radiator, resulting in a hot engine and no heat at the heater. Then when a pocket of water passes through the system, the temperature gauge quickly falls as the water absorbs the heat from the engine. The hot water that cools the engine is where the heater gets it's heat from as well, so when water passes through the heater core, the heater works, but when it's filled with air, it doesn't.