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How does the cooling system work

Tiny
VISH4369
  • MEMBER
  • 2004 HYUNDAI SONATA
  • 90,000 MILES
I have a manual drive with four cylinders. Recently I am having over heating issues in stop and go traffic. I am trying to understand its system. Usually thermostat is located at upper hose housing for this car it is at lower hose housing. Cars upper hose is hot at operating temperatures but lower is bad cold almost all the time, but I can feel it as warm and as hot as upper hose occasionally. Can anyone explain its cooling system? Is the thermostat letting the cooling from lower hose when engine become hot?
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Sunday, December 17th, 2017 AT 5:04 PM

36 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
It really sounds like the thermostat is not opening to allow coolant to circulate that would explain the upper hose hot and the bottom hose cold. That is if you have not changed the coolant recently otherwise you could have air in the cooling system. Let me find a guide for you.
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Here is a guide for overheating let me know what you find:

https://www.2carpros.com/articles/engine-overheating-or-running-hot
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
VISH4369
  • MEMBER
  • 32 POSTS
My radiator fans are not kicking on at operating temperatures, fan and motor are working fine. When I pull the coolant temperature sensor plug fans kicks on but it is not kicks on when plugged at operating temperatures. And my radiator is also hot at upper end and thermostat for my car is at lower hose.
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
From the fan coming on when unplugging the temperature sensor but not coming on from warming up like before it heats that sounds like a bad coolant temperature sensor. You said the lower hose stayed cold when it got to operating temperature. That is why I was talking about a thermostat. But I also saw that you said it cooled down while moving. So the fan not operating correctly would make sense with that happening.
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
VISH4369
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  • 32 POSTS
I changed the sensor today. Then I top off the coolant and was making sure by checking for the bubbles. I kind of see bubbles like three or four at a times and do not see them for a while and see them again (it was raining slightly assuming it is rain causing it bubble, correct me if I am wrong and educate me if it is head gasket related issue) after I changed the sensor and ran car in the first engine was creeping hot my fans kick on for a while still engines over heating so I shut it off. I ran the car again then it creeped little over operating temperatures and come down again then it never creeped up again until now. Need explanation why it creeped hot in the case if you can please. Other than that everything seems fine now but I will be checking it for a week before I ignore it. Thanks for your help.
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
VISH4369
  • MEMBER
  • 32 POSTS
It did not work. After running it for an hour it is overheating again.
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
So are both upper and lower radiator hoses getting too hot to hold? You would need to rent a chemical block tester from Autozone to see if there was exhaust gasses entering the cooling system. They will make you buy the fluid for the tester.
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
VISH4369
  • MEMBER
  • 32 POSTS
That means it is a head gasket? Oh no, I just bought this car.
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
SATURNTECH9
  • MECHANIC
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Are both the upper and lower radiator hoses getting too hot to hold at normal operating temp?That's why your doing the chemical block tester to see if there is exhaust gasses in the cooling system.
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
VISH4369
  • MEMBER
  • 32 POSTS
It's not Everytime only sometimes I will say 1 day every 10 days. Today it didn't happen. And it didn't over heat too
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
So one day out of every 10 the hoses are too hot to hold and that's when it doesn't overheat?
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
VISH4369
  • MEMBER
  • 32 POSTS
I don't know today hose is hot and it's over heating it's creeps high fast if heat is on. Raditor fan not kicking on by itself again. I unplug the sensor fans turning plugged in reached almost to red but fan didn't kick on
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
SATURNTECH9
  • MECHANIC
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I would run a chemical block tester on it.
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
VISH4369
  • MEMBER
  • 32 POSTS
If I have a head gasket problems or exhaust leaking into cooling system fans won't kick on?
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
The fan should kick on but you also said both upper and lower hose aren't always getting too hot to hold. So it crazy how so many issues you seem to have.I would replace the thermostat since you said that both upper and lower radiator hoses aren't getting too hot to hold at operating temp.
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
VISH4369
  • MEMBER
  • 32 POSTS
Upper getting hot lower not getting hot until I drive like 50 miles
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
SATURNTECH9
  • MECHANIC
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Yeah I would replace that thermostat
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
VISH4369
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  • 32 POSTS
I will do that tomorrow
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
SATURNTECH9
  • MECHANIC
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Sounds good
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Sunday, October 25th, 2020 AT 12:30 PM
Tiny
VISH4369
  • MEMBER
  • 32 POSTS
I replaced thermostat even the old one still looks good. Flushed the coolant. Yesterday it seemed fine that fan were turning on automatically and shutting off. But this morning its was foggy snowing and while I was car indicator creeping up since I have an obd scanner I checked the coolant temp it was about 195 F I pulled over checked for fans. There were dead and not coming on. Indicator reached all the up obd sensor reading 195 F. Is 195 F is the ultimate temp or my sensor bad again because its a new one
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Sunday, October 25th, 2020 AT 12:30 PM

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