Cadillac STS The newest installation of the performance sedan from Cadillac, having replaced the Seville

Overheating question that will stump you!!!

  #1  
Old 03-07-2011, 05:03 PM
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Exclamation Overheating question that will stump you!!!

Riddle me this...

Why would my 1999 STS overheat at idle, but cool off once the engine is brought up to 2K RPMs? And it doesn't matter if you're driving or standing still!

The fans don't come on, but this is the weird (er?) part...

if you're rolling down hill doing 50 it will still over heat unless you drop down a gear and get the RPMs above 2K.

I've changed the water pump and thermostat. And the coolant cap twice!

The tube that goes from the coolant tank to the engine is clear as well.


What the heck is going on?

I love Caddies (this is my 4th) but the overheating problems (with my last 96 Concourse, as well) are driving me to drink!


HEEEEELLLLLP!!!!!
 
  #2  
Old 03-08-2011, 03:11 AM
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have you been checking the coolant level. i had this happen to me and noticed i was low and filled it up. i did this a few times before finding out my engine was actually burning the coolant due to gasket issues. you said you replaced T-stat and water pump and cap and still over heating but the FANS are not comming on. that would be my first thing i would check. look at fuses and relays. next see if the top coolant hose is filled with air by squeezing it. do this after you have driven awhile otherwise the air in coolant hose will leak out after sitting long enough so you wont notice the air. If there is air in the cooling system this will act like a blockage and keep coolant from flowing efficiently. This would probly be why running at 2k or more helps because the water pump forces enough coolant to push the air pocket out of the way. If you are wondering where the air is coming from you will probly not want to hear the bad news.
 

Last edited by 92_Daddylac; 03-08-2011 at 03:22 AM.
  #3  
Old 03-25-2011, 05:15 PM
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Hi Guys,

I have a 1997 Deville. After driving about 5 miles the coolant temperature seems to go to 212 to 220. Is this normal or should I worry. Thanks.
 
  #4  
Old 03-25-2011, 07:28 PM
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Originally Posted by 92_Daddylac View Post
have you been checking the coolant level. i had this happen to me and noticed i was low and filled it up. i did this a few times before finding out my engine was actually burning the coolant due to gasket issues. you said you replaced T-stat and water pump and cap and still over heating but the FANS are not comming on. that would be my first thing i would check. look at fuses and relays. next see if the top coolant hose is filled with air by squeezing it. do this after you have driven awhile otherwise the air in coolant hose will leak out after sitting long enough so you wont notice the air. If there is air in the cooling system this will act like a blockage and keep coolant from flowing efficiently. This would probly be why running at 2k or more helps because the water pump forces enough coolant to push the air pocket out of the way. If you are wondering where the air is coming from you will probly not want to hear the bad news.
i know some Northstars have a BURP valve atop of engine somewhere .. do you know if this model has one?

also, some GM's turn the fans on anytime the A/C is on .. does that apply to this model?


.

.
 
  #5  
Old 03-26-2011, 05:23 AM
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Originally Posted by coral321 View Post
Hi Guys,

I have a 1997 Deville. After driving about 5 miles the coolant temperature seems to go to 212 to 220. Is this normal or should I worry. Thanks.

you should be just fine as long as you dont go over 225 if so check things out such as leaks or low coolant level.
 
  #6  
Old 03-28-2011, 07:22 AM
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check your coolant temperature sensor
 
  #7  
Old 03-29-2011, 08:03 AM
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Thanks guys. I appreciate your inputs. I am going to check all of the things all of you have mentioned. Will let you know after everything checks out.

Thanks again.
 
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