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Fluctuating temperature gauge

Tiny
KINGD2316
  • MEMBER
  • 2001 HYUNDAI SANTA FE
  • 2.7L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 149,195 MILES
My temperature gauge keeps getting higher when I first crank it then it will sometimes drops back down to where it normally sits at. Other times it stays a little on the high side. The radiator and reservoir are both full. The fan comes on like it should. I replaced the thermostat two days ago. What could be wrong and should I be worried about the gauge movement?
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Friday, October 11th, 2019 AT 7:12 PM

7 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,289 POSTS
Welcome to 2CarPros.

A few different things can cause this. Are you sure there is no air left in the system since the thermostat was replaced? Also, based on years and miles, did you flush the cooling system to clean it?

https://www.2carpros.com/articles/coolant-flush-and-refill-all-cars

Even a faulty radiator cap can cause it to overheat. By staying pressurized, the boiling point is raised. Do the radiator hoses get hard with pressure when the engine warms up?

Let me know,
Joe
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Friday, October 11th, 2019 AT 8:39 PM
Tiny
KINGD2316
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  • 5 POSTS
I will have to check and do the things you mentioned.
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Saturday, October 12th, 2019 AT 5:26 AM
Tiny
KINGD2316
  • MEMBER
  • 5 POSTS
Could any of these 4 codes cause the temperature to fluctuate?
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Saturday, October 12th, 2019 AT 5:27 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,289 POSTS
Welcome back:

With those codes, the engine has to be running in what is called a closed loop. Basically, the computer makes the fuel mixture rich enough for it to run regardless of temp. I would like to say they wouldn't, but if the engine is running hotter due to a richer than normal fuel mixture, it could.

Joe
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Saturday, October 12th, 2019 AT 7:08 PM
Tiny
KINGD2316
  • MEMBER
  • 5 POSTS
Well, I checked the water whe.
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Saturday, October 12th, 2019 AT 7:37 PM
Tiny
KINGD2316
  • MEMBER
  • 5 POSTS
I am about to go through the things you listed in your first response. Yesterday afternoon I checked the water level in the radiator and there was white stuff in it. So I am going to flush it. Is there certain kind of flush you would recommend?
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Sunday, October 13th, 2019 AT 1:49 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,289 POSTS
Welcome back:

That is a concern. Can you upload a pic of what you are seeing? Also, I'm not supposed to recommend any products because then people feel we are getting a kick back and that isn't the case. However, any of the original brands all work well. Products from Prestone, Blue Devil, Gunk and so on are all good.

Let me know. Also, if possible, upload a pic. I'm concerned there is oil getting by a head gasket. Take a look through this link to see if anything mirrors what you are seeing. Also, a bad head gasket can cause temperature fluctuations.

https://www.2carpros.com/articles/head-gasket-blown-test

Take care,
Joe
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Sunday, October 13th, 2019 AT 7:36 PM

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