Hi, I have a 2003 Hyundai sonata GL with a 2.4L DOHC with 210000 miles on the original power/drivetrain. I've noticed that it likes to overheat. -coolant- clean as can be, and new -both fans work -no leaks or air in system -new thermostat -leak tested head gasket However, I think it's sensor/ ground fault, here's my reasoning. -the over heat will get worse with vehicle runtime -it doesn't make any sense, cooler uphill, hotter on the highway -the more electric loads the worse, compressor, headlights, blower -when you turn off loads it will go down as fast as it can (ECM must have a max gauge speed.) -yes it is phoenix Arizona -ive tested it with a ir thermometer when overheating and temps range from 180(lower rad hose) to 203F as a max temp. -no coolant loss or steam/ bubbling of sort, it does run a little lean because it thinks its hot and compensates. -ive driven ~30 miles with it in the "red zone" and no problems. -when It overheats and I turn it off and put it in ignition it will be back at operating temp, lower than halfway mark. -ive seen forums with others with similar problems.

Comments (2)
No. 1-2
Stevetrd
Stevetrd

Hi scotty, ive watched the video and done some testing, if the car is warm, (a little below operating temp) and I turn the ignition without turning the car on, the temp gauge will rise normally, if I turn the blower and headlights on, I can physically see the temp gauge rise with the car off. Along with other testing ive done the combustion gas test with the blue fluid, it stayed blue, also ive bought a new radiator cap and done a leak down test and looked at all coolant hoses, fittings, and freeze plugs with a borescope camera, I also looked at the hvac drain during the leak down test which showed no pressure loss. At this point im looking in the area of the temp sensor, wiring, grounds, and possibly the ecm for either replacing or solder reflowing.

Scotty Kilmer
Scotty Kilmer

Editor

do this video https://www.youtube.com/watch?v=evpaTW2WJ5Y