Car overheating only on long drives and after being driven for 20-30min+

My 2016 Kia Cadenza overheats after driving it for over 30 min. never on idle.

About 3 weeks ago i felt that my AC would stop working mid ride after taking it to 2 different mechanics i was told i would need a new compressor. I went ahead and went with a mechanic shop that ive been going to for sometime now for other vehicles.

The same day that i leave with my new AC compressor my engine started to heat up. i take it back and they advise me that it can be either a bad thermostat or sensor. I end up replacing the thermostat, radiator cap, sensor and thermostat housing/holder. the mechanic and i have purged all the air at this point from the system. i have done a flush, radiator cleaner, flush again. they have pressure leak tested it and i have no leak. Both fans work and kick on when they are supposed to. the coolant that i seem to be loosing comes from it all backing up into the reservoir and over filling instead of going back into the radiator. at idle, with the AC on high the car will never overheat. when i drive it like i mentioned before for over 30 min i start to see it over heat . I drive for a living and i really need some help with this one. At this point the mechanic is saying i need to replace the water pump or radiator but that doesnt seem like it what will fix it because of what i have stated. no motor shaking, no smoke at ignition or while driving so i DONT THINK its a headgasket. — Desperate to confidently get back on the road

Has anyone checked the AC condenser for debris?

Here’s a before and after image.


to a certain degree i have cleaned it with a water hose pressure knob. i will upload pics in a bit but it does not look anywhere near that dirty. Thank you for the advice though!

Unless you use one of these, you can’t properly clean an AC condenser.


Does it overheat on a hwy or in town as well?

you said both fans come on. does that mean the radiator fan comes on when it is supposed to and then the a*c fan comes on when you put the a/c on? or did you just see both fans on and think they are working properly?
If it is the latter, then it can be a problem with the fan control motor. and the radiator fan is not coming on, and only works when the a/c is on. that would cause it to overheat when driving without the a/c on but be ok when the a/c is turned on.

both. so ive determined it heats up because air is trapped in the cooling system. coolant gets pushed into the reservoir but isnt allowed to get back into the cooling system. like i mentioned before the only reason i think i waste coolant is from what gets pushed back into the reservoir and then that gets overfilled and shot out

I would spend $10 on a (check reviews - some of them are bogus!) chemical exhaust tester and checked the head gasket. It may not leak coolant (neither internally nor externally) but push exhaust gases into the water jacket thus creating gas pockets.

Has the radiator cap been tested to see if it holds the proper pressure?


would a test of me driving without ac at all determine this? ive turned the ac off and turned the heat on to lower engine temp and that lowers the temp.

That’s just using the smaller radiator in the cooling system to lower the coolant temp.

The means the problem lies in the main cooling system.


1 Like

ive replaced the thermostat and radiator cap twice. i got one with a pressure release valve to get the pressure out so i can add coolant without having to wait for the car to cool down 100%

start your vehicle. pop your hood open and let your engine get to operating temp. with the A/C off and see if the radiator fan comes on.

ive done this and gotten it up to 2500 rpm for a little bit to " simulate" driving rpms. and the fan does come on. it never gets hot on idle :confused: ive done this a few times to purge all the air out with a radiator funnel actually

another thought. if your vehicle has a radiator cap and a screw on overflow cap. it could be a bad overflow cap.

the reservoir has a snap cap, the radiator has a screw on cap

im gonna try this i didnt know this existed. anyone of these you recommend over another. Both have great reviews

you might still have air in your system. you may need to vacuum bleed it.

Know-How Notes: Using a Radiator Vacuum Tool » NAPA Know How Blog (

Does the heat work properly?

1 Like