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Discussion Starter #1
i have a 98 sts and this just started a month ago my car was always in the middle on the instrument cluster now its on the line after the middle , when i drive it goes back towards the middle but never on the middle , when i get to a red it goes straight to the line after the middle idk if i need a compression check, or a new thermostat or water pump ????/any suggestion would be nice
 

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Where do you live? How hot does it get there? On my previous STS' it would sometimes go half a line past the middle mark if I recall.
 

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Sedan de Ville, CTS
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Check out a few things on car:

1. Is anti-freeze full in overflow container--up to lines.
2. Have you been adding anti freeze?
3. Climb under car with flashlight and look for drips--other than condensation from a/c unit. I do this at night.
4. Do you smell any anti-freeze?
5. Carefully check bottom area of radiator for leaks.
6. Carefully check bottom of hoses and hose clamps for leakage.
7. There is a hose at bottom of overflow tank. Need to pull tank loose to check that.
8. Check heater hoses for leaks.
9. Check bypass hose at water pump for leaks. Check water pump for leaks; there is a weep hole somewhere on water pump. Any stains at weep hole?

If you do not smell any a/f, and if you have not been adding any, your system is likely secure.

If car has more than 50k miles on it, it would not hurt to change thermostat, using required stat (190 degrees???)

Has anyone ever put 'stop it' in radiator. One container is ok. If, however, someone put a couple in it, radiator could be partially clogged.

Simplest thing is to take it to a radiator shop and leave it overnight. Not expensive for diagnosis. Maybe $30 or less. Sometimes free.

By the way, a radiator shop is a good place to take a leak.
 

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1997 SLS
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550 Posts
Back on topic :) I have a friend with a 95 Lumina that's doing the same thing. I did all the checks for him, and other than the coolant being 4 years old, could not find anything visibly wrong. But like you mentioned, his gage would approach red-line. He could solve it by turning of the A/C. I thought it might be a partially blocked thermostat. I think Northstar thermostats are in a bad location...behind the water pump? Not sure.
 

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Cadillac seville sts/ srx
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worst case is you have a head gasket blown i have learned from personal experience that you dont need to see radiator fluid for it to be fubar it may overheat when the motor is being worked hard or up hill... i hope for your sake its a quick fix... if not trade the car in or shell out 4-5k :eek:
 

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'94 Seville STS N*
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i really wouldn't be too worried about one line past the middle when idle.

my northstar will go from 198 degrees on the freeway to ~220 at idle in traffic.

if i had the non-digital coolant temp, i'd imagine that would be a line up from the middle.
 

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94 ETC,97 STS
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If the AC is off the fans do not come on until 225F. (If AC on the fans should be on.)

If you're moving it stays below that. Under load or in stop and go driving it will go up to that. It might be normal. Are you losing coolant?

Z06bigbird gave you a nice list.:highfive:
 

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1997 SLS
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JC316: Is a thermostat change-out described somewhere on tech tips? I could not find it, but maybe it's way back in the archives. I thought the thermostat was behind the water pump - maybe not. Does anyone have a list on how to do this, if it is Mysts98's problem?
 

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JC316: Is a thermostat change-out described somewhere on tech tips? I could not find it, but maybe it's way back in the archives. I thought the thermostat was behind the water pump - maybe not. Does anyone have a list on how to do this, if it is Mysts98's problem?

You take the airbox off, disconnect the lower radiator hose from the water pump, take the 2 10mm bolts out of the thermostat housing and remove the thermostat.

The lower radiator hose goes right into the thermostat. It took me 10 minutes to change it.
 
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