The car overheats when sitting still with engine running, new thermostat installed, coolant is good. Fans run with air on
Where is the thermal fan switch located? on 2004 Hyundai Sonata
im having the same problem with a honda accord 2001 this is most likely your problem you need to get a radiator cooling switch part# TU 188 at auto zone and also you might want to get a coolant temp sensor part # su4006 at autozone if your fans work with ac on then they are not getting a signal from the brain telling them to run when the car is hot so your coolant temp sensor is most likely bad or the fan radiator coolant temp sensor is bad my advice buy both there not that expensive i got both for under 50 bucks
Where is the radiator cooling switch located?