Hello, new to the forum

Working on a 2004 Sonata for my sons girl friend. It came to me with an overheating problem. I Was told that when driving it with AC, it would start to overhead. She would turn off the AC and turn the heat on to help expel some of the heat at which point the gauge would begin to drop. Now I started checking things. The first thing I did was get online to see what others were experiencing. The symptoms I was seeing, were what others found the coolant sensor to be the fix. I had noticed that the fans were not on. So I put a new sensor in, turned on the car and the AC and the fans began to run. I thought it was all good. So I drove it down to the store at which point it overheated. Next step was to test the thermosat. I put in boiling water and watched it open. Still decided to throw a new one in anyways. Last night I had it running and watched it climb up to normal temp. I thought I had it. Both the upper and lower hoses seemed to be normal temps, but the gauge was climbing higher. I turned on the AC to get the fans to kick on, which they did, but the temp gaugeclimbed to the top. Didnt appear the fans were doing anything. Then I started to figure out why the fans will not come on with the AC turned off. Messed with all the relays, like six of them. If I unplug the coolant sensor, the fans turn on. I then pulled each relay to see if they affected anything. Each one pulled turned the fans to lower or higher speeds, or simply turned them off. So I think they are fine. So, what causes the fans to turn on if the AC is turned off? Then I noticed that then when I turned the car off, obviously the temp gaugedropped to zero. Then if I started it again, the gauge showed just below the normal temp, but would start to climb. If it were hot and the gauge showing that when the car was running, why would it not jump to the top when the car was running again? Confused. I thought then next step may be the water pump, but the way I could feel the temps on the hoses, I felt there was circulation. Meaning, as the top hose got hot, the lower hose was still cold, but did warm up to to open the thermostat. How would you check for certain water flow?

 

While the engine is cold, take off the radiator cap
Make sure it has enough coolant or add water til you see it at the top of radiator
Start engine. Watch as it warms up. At first there should be no movement of coolant
Flashlight helps. Then when the thermostat opens, there should be movement or flow.
Coolant may heat up and over flow out of opening.
Do the fans turn on when it reaches normal operating temps?
If there is flow and fans do turn on then radiator's capacity to dissipate heat has diminished.
Replace radiator.

Note: Turning on heat inside of cabin and able to see the temp gauge go down
Also indicates radiators is not cooling. Whether it is due to fans not turning on
Or, the radiator itself.

 

Thank you for replying, it sure is appreciated. So I followed your directions. Radiator is full, started the car. It started to warm and the coolant comes to the top and overflows. Watched the gauge until it hit normal temps. The fans at this point do not turn on. I hit the AC button and the temp gauge, with in 20 seconds climbed to almost high. Turned it off and the gauge came down to just above normal. Another 10 minutes and it was up to 3/4 way. Not fans. The upper hose is hot, but hose to thermostat is only warm. Still no flow from the radiator. The temp gauge was just under the high hot mark when I turned it off. No fans came on unless the AC is on. If I squeeze the lower hose, it pushes coolant out the top of the radiator. To me I am leaning towards a bad water pump. No flow is one sigh correct? I am going to pull the plug on the radiator to see if it will drain to verify a block radiator.

 

Sometimes need to rev engine to see if there is coolant flow.
Cooling fan should have turned on
Turning A/C turned both fans on?
If yes then fans are working
Maybe temp sensor not working to turn fan on?

Leaning towards water pump?
When thermostat opens, and engine is rev up a bit, there should be flow
If there was no flow at all then it would heat up quite fast
When was the last time the timing belt was changed??

When you turned heater on with fan, the temp did go down
Flow in and out of heater core must mean there is flow from water pump
I am still suspecting loss of cooling capacity of radiator
But would certainly like to see the cooling fans kick on

 

Thanks again.
It did take some time to heat up, I would say 10 minutes to get to normal.
Turning on AC, yes, both fans turn on.
The Temp sensor is new and thermostat as well
The car is not mine so I am not sure when the timing belt was last changed. I can ask, but she may not know.
When turning heater on, there is heat and it does help drop the temp. So I agree, that would indicate water flow.
I will again check flow while rev'ing the engine tonight.

Could it possibly be the new sensor is jacked up? When I disconnect the connector from the sensor, the fans turn on. So I may need to check the connector itself, maybe I have bent something in side the connector. I will report back when I have something.

Thanks again.

 

My sister in laws 2015 Elantra with 1.8 engine and auto trans Elantra is overheating after replacing water pump, thermostat and radiator. Hyundai dealer is stumped. Do you have any answers or clues?

 

That is a short post with little information.
So, all anyone can do is guess at the issue

Need to check to see if the electric fans are turning on.
Usually there are two fans
One for the radiator and the other for the AC condenser
Turning on the AC should turn on both fans
From a cold start, the electric fan should turn on when engine is at operating temp
If engine is running hot then see if fan is working
If not working then could be fan or coolant temperature sensor

Other than that, there is checking the flow of coolant to see if water pump and thermostat are working
Check coolant level. if there is a leak in the system?

Good luck
Let us know if you fix it and what that fix was