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2010 hyundai sonata overheats in odd ways
2010 Hyundai Sonata

2010 Hyundai Sonata overheats in odd ways

(2010 Hyundai Sonata)
My 2010 Sonata has been kind of a terror the last couple of months. It has 123,XXX miles on it and bought it from a dealership with 120,000. The oil was good and all I had to do from the start was new tires and rear sway bar links. Then a couple weeks later I started getting Engine Trouble lights after I noticed the engine temperature gauge stayed cold. Mechanic said the thermostat was stuck open. So, I replaced it and the antifreeze. The car ran fine for a couple weeks, no temperature issues or anything, then all the bad stuff started happenng. The temperature gauge started being erratic. It would climb to the max a few minutes after driving and the engine wasn't even hot than the gauge would instantly drop and climb back up and just overall super erratic. I took it to my mechanic who said it was a bad coolant temperature sensor and he replaced it. Amidst other problems, a couple weeks later, it's kind of doing the same but not as erratic.
What seems to make the problem better or worse? Extremely erratic. Has good days and bad days without any changes
How long have you had this problem? A couple months
Tags: hyundai, sonata
1 answer & 2 comments
Popular Answer
on September 30, 2019

Connect scan device that has live sensor data - does scan tool coolant temperature data agree with the in dash temperature gauge readings ?

Do you understand the significance of this test?
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on September 30, 2019
Can I rent one of those tools from AutoZone do you think?
I think I understand why to test that.
The thing is A. It only does that for the first 15 minutes of driving, then the needle settles down and acts normal. It still overheats slowly as I'm driving. B. I know the fan does not kick on when it starts to overheat. C. The start of driving when it is erratic makes me wonder if there is air in the system. The heater always blows hot air though. I've never felt it fluctuate.
I'm not getting the classic signs of head gasket issues like oil in coolant, leaks, running rough or missing, etc. I know it blows grey/blue smoke when you hit the accelerator hard, but that is most likely from the valve O-rings leaking oil.
on September 30, 2019

You can buy a ‘code reader’ that has sensor data for approximately $30.00.
(Google) - - Amazon.

IF scan temp = temp gauge then there is a problem within the cooling system.

IF scan data is not same - there is an electrical problem within the gauge circuit.

Plus I think every vehicle owner should have some type of an onboard diagnostic tool.

Can leave scan tool connected while operating vehicle - just doesn’t be distracted by it while driving - pull over to view data.

Good luck!
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on September 30, 2019

Connect scan device that has live sensor data - does scan tool coolant temperature data agree with the in dash temperature gauge readings ?

Do you understand the significance of this test?
Sign in to reply
on September 30, 2019
Can I rent one of those tools from AutoZone do you think?
I think I understand why to test that.
The thing is A. It only does that for the first 15 minutes of driving, then the needle settles down and acts normal. It still overheats slowly as I'm driving. B. I know the fan does not kick on when it starts to overheat. C. The start of driving when it is erratic makes me wonder if there is air in the system. The heater always blows hot air though. I've never felt it fluctuate.
I'm not getting the classic signs of head gasket issues like oil in coolant, leaks, running rough or missing, etc. I know it blows grey/blue smoke when you hit the accelerator hard, but that is most likely from the valve O-rings leaking oil.
on September 30, 2019

You can buy a ‘code reader’ that has sensor data for approximately $30.00.
(Google) - - Amazon.

IF scan temp = temp gauge then there is a problem within the cooling system.

IF scan data is not same - there is an electrical problem within the gauge circuit.

Plus I think every vehicle owner should have some type of an onboard diagnostic tool.

Can leave scan tool connected while operating vehicle - just doesn’t be distracted by it while driving - pull over to view data.

Good luck!

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